Techniques of Water-Resources Investigations of the United States Geological Survey

Chapter A1 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES IN WATER AND FLUVIAL SEDIMENTS By Marvln J. Fishman and Linda C. Frledman, Editors

First Edition 1970 Second Edition 1979 Third Edition 1989

Book 5 LABORATORY ANALYSIS UNITED STATES DEPARTMENT OF THE INTERIOR MANUEL LUJAN, JR., Secretary

GEOLOGICAL SURVEY

Dallas L. Peck, Director

f

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1989

For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. PREFACE A series of chapters on techniques describes methods used by the U.S. Geological Survey for planning and conducting water-resources investigations. The material is arranged under major subject headings called books and is further subdivided into sections and chapters. Book 5 is on laboratory analyses; section A is on water. The unit of publication, the chapter, is limited to a narrow field of subject matter. "Methods for Determination of Inorganic Substances in Water and Fluvial Sediments" is the first chapter under section A of book 5. The chapter number includes the letter of the section. This chapter was prepared with the assistance of many chemists and hydrolo gists of the U.S. Geological Survey as a means of documenting and making available the methods used by the U.S. Geological Survey to analyze water, water-sediment mixtures, and sediment samples. Any use of trade names, commercial products, manufacturers, or distributors is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey. This chapter supersedes "Methods for Determination of Inorganic Sub­ stances in Water and Fluvial Sediments" by M. W. Skougstad, M. J. Fishman, L. C. Friedman, D. E. Erdmann, and S. S. Duncan (U.S. Geological Survey Techniques of Water-Resources Investigation, book 5, chapter Al, 1979) and "A Supplement to Methods for the Determination of Inorganic Substances in Water and Fluvial Sediments" by M. J. Fishman and W. L. Bradford (U.S. Geological Survey Open-File Report 82-272, 1982). CONTRIBUTORS

Carlos E. Arozarena Arthur J. Horowitz Delora Boyle Edward W. Matthews Randall M. Brown Berwyn E. Jones Edward H. Drake Gary R. Ferryman Marvin J. Fishman Grace S. Pyen Linda C. Friedman Janet Robinson John Garbarino James M. Schoen Arthur Hedley Edward J. Zayhowski

The time and effort spent by Catherine Vick and Nancy L. Newell in the typing and preparation of this manual are gratefully acknowledged. Also acknowledged are the many helpful suggestions and comments from person- nel in the Denver and the Atlanta Central Laboratories. TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS OF THE U.S. GEOLOGICAL SURVEY

The U.S. Geological Survey publishes a series of manuals describing procedures for planning and conducting specialized work in water-resources investigations. The manuals published to date are listed below and may be ordered by mail from the U.S. Geological Survey, Books and Open- File Reports Section, Federal Center, Box 25425, Denver, Colorado 80225 (an authorized agent of the Superintendent of Documents, Government Printing Office). Prepayment is required. Remittance should be sent by check or money order payable to U.S. Geological Survey. Prices are not included in the listing below as they are subject to change* Cur­ rent prices can be obtained by writing to the USGS address shown above. Prices include cost of domestic surface transportation. For transmittal outside the U.S.A. (except to Canada and Mex­ ico) a surcharge of 25 percent of the net bill should be included to cover surface transportation. When ordering any of these publications, please give the title, book number, chapter number, and "U.S. Geological Survey Techniques of Water-Resources Investigations."

TWRI 1-D1. Water temperature—influential factors, field measurement, and data presentation, by H.H. Stevens, Jr., J.F. Ficke, and G.F. Smoot. 1975. 65 pages. TWRI 1-D2. Guidelines for collection and field analysis of ground-water samples for selected unstable constituents, by W.W. Wood. 1976. 24 pages. TWRI 2-D1. Application of surface geophysics to ground-water investigations, by A.A.R. Zohdy, G.P. Eaton, and D.R. Mabey. 1974. 116 pages. TWRI 2-D2. Application of seismic-refraction techniques to hydrologic studies, by P.P. Haeni. TWRI 2-E1. Application of borehole geophysics to water-resources investigations, by W.S. Keys and L.M. MacCary. 1971. 126 pages. TWRI 2-F1. Application of drilling, coring, and sampling techniques to test holes and wells, by Eugene Shuter and W.E. Teasdale. TWRI 3-A1. General field and office procedures for indirect discharge measurements, by M.A. Benson and Tate Dalrymple. 1967. 30 pages. TWRI 3-A2. Measurement of peak discharge by the slope-area method, by Tate Dalrymple and M.A. Benson. 1967.12 pages. TWRI 3-A3. Measurement of peak discharge at culverts by indirect methods, by G.L. Bodhaine. 1968. 60 pages. TWRI 3-A4. Measurement of peak discharge at width contractions by indirect methods, by H.F. Matthai. 1967.44 pages. TWRI 3-A5. Measurement of peak discharge at dams by indirect methods, by Harry Hulsing. 1967. 29 pages. TWRI 3-A6. General procedure for gaging streams, by R.W. Carter and Jacob Davidian. 1968. 13 pages. TWRI 3-A7. Stage measurements at gaging stations, by T.J. Buchanan and W.P. Somers. 1968. 28 pages. TWRI 3-A8. Discharge measurements at gaging stations, by T.J. Buchanan and W.P. Somers. 1969. 65 pages. TWRI 3-A9. Measurement of time of travel and dispersion in streams by E.F. Hubbard, F.A. Kilpatrick, L.A. Martens, and J.F. Wilson, Jr. 1982. 44 pages. TWRI 3-A10. Discharge ratings at gaging stations, by E.J. Kennedy. 1984. 59 pages. TWRI 3-A11. Measurement of discharge by moving-boat method, by G.F. Smoot and C.E. Novak. 1969. 22 pages. TWRI 3-A12. Fluorometric procedures for dye tracing, by J.F. Wilson, Jr., E.D. Cobb, and F.A. Kilpatrick. 1986.41 pages. TWRI 3-A13. Computation of continuous records of streamflow, by E.J. Kennedy. 1983. 53 pages. TWRI 3-A14. Use of flumes in measuring discharge, by F.A. Kilpatrick and V.R. Schneider. 1983. 46 pages. TWRI 3-A15. Computation of water-surface profiles in open channels, by Jacob Davidian. 1984. 48 pages. TWRI 3-A16. Measurement of discharge using tracers, by F.A. Kilpatrick and E.D. Cobb. 1985. 52 pages. TWRI 3-A17. Acoustic velocity meter systems, by Antonius Laenen. 1985. 38 pages. TWRI 3-A18. Determination of stream reaeration coefficients by use of tracers, by F.A. Kilpatrick, R.E. Rathbun, N. Yotsukura, G.W. Parker, and L.L. Delong. [in press]. TWRI 3-B1. Aquifer-test design, observation, and data analysis, by R.W. Stallman. 1971. 26 pages. *TWRI 3-B2. Introduction to ground-water hydraulics, a programmed text for self-instruction, by G.D. Bennett. 1976. 172 pages. TWRI 3-B3. Type curves for selected problems of flow to wells in confined aquifers, by J.E. Reed. 1980. 106 pages. TWRI 3-B4. Regression modeling of ground-water flow, by R.L. Cooley and R.L. Naff, [in press].

Spanish translation also available. TWRI 3-B5. Definition of boundary and initial conditions in the analysis of saturated ground-water flow systems—An introduction, by O.L. Franke, T.E. Reilly, and G.D. Bennett. 1987. 15 pages. TWRI 3-B6. The principle of superposition and its application in ground-water hydraulics, by T.E. Reilly, O.L. Franke, and G.D. Bennett. TWRI 3-C1. Fluvial sediment concepts, by H.P, Guy. 1970. 55 pages. TWRI 3-C2. Field methods of measurement of fluvial sediment, by H.P. Guy and V.W. Norman. 1970. 59 pages. TWRI 3-C3. Computation of fluvial-sediment discharge, by George Porterfield. 1972. 66 pages. TWRI 4-A1. Some statistical tools in hydrology, by H.C. Riggs. 1968. 39 pages. TWRI 4-A2. Frequency curves, by H.C. Riggs. 1968. 15 pages. TWRI 4-B1. Low-flow investigations, by H.C. Riggs. 1972. 18 pages. TWRI 4-B2. Storage analyses for water supply, by H.C. Riggs and C.H. Hardison. 1973. 20 pages. TWRI 4-B3. Regional analyses of streamflow characteristics, by H.C. Riggs. 1973. 15 pages. TWRI 4-D1. Computation of rate and volume of stream depletion by wells, by C.T. Jenkins. 1970. 17 pages, TWRI 5-A1. Methods for determination of inorganic substances in water and fluvial sediments, by M.W. Skougstad and others, editors. 1979. 626 pages. TWRI 5-A2. Determination of minor elements in water by emission spectroscopy, by P.R. Barnett and E.G. Mallory, Jr. 1971. 31 pages. TWRI 5-A3. Methods for the determination of organic substances in water and fluvial sediments, edited by R.L. Wer- shaw, M.J. Fishman, R.R. Grabbe, and L.E. Lowe. 1987. 80 pages. TWRI 5-A4. Methods for collection and analysis of aquatic biological and microbiological samples, edited by P.E. Greeson, T.A. Ehlke, G.A. Irwin, B.W. Lium, and K.V. Slack. 1977. 332 pages. TWRI 5-A5. Methods for determination of radioactive substances in water and fluvial sediments, by L.L. Thatcher, V. J. Janzer, and K.W. Edwards. 1977. 95 pages. TWRI 5-A6. Quality assurance practices for the chemical and biological analyses of water and fluvial sediments, by L.C. Friedman and D.E. Erdmann. 1982. 181 pages. TWRI 5-C1. Laboratory theory and methods for sediment analysis, by H.P. Guy. 1969. 58 pages. TWRI 6-A1. A modular three-dimensional finite-difference ground-water flow model, by M.G. McDonald and A.W. Har- baugh. [in press]. TWRI 7-C1. Finite difference model for aquifer simulation in two dimensions with results of numerical experiments, by P.C. Trescott, G.F. Pinder, and S.P. Larson. 1976. 116 pages. TWRI 7-C2. Computer model of two-dimensional solute transport and dispersion in ground-water, by L.F. Konikow and J.D. Bredehoeft. 1978. 90 pages. TWRI 7-C3. A model for simulation of flow in singular and interconnected channels, by R.W. Schaffranek, R.A. Baltzer, and D.E. Goldberg. 1981. 110 pages. TWRI 8-A1. Methods of measuring water levels in deep wells, by M.S. Garber and F.C. Koopman. 1968. 23 pages. TWRI 8-A2. Installation and service manual for U.S. Geological Survey monometers, by J.D. Craig. 1983. 57 pages. TWRI 8-B2. Calibration and maintenance of vertical-axis type current meters, by G.F. Smoot and C.E. Novak. 1968. 15 pages.

VI CONTENTS

Page Page Preface ————————————————————————— iii Analytical techniques—Continued Contributors—————————————————————— iv Atomic absorption spectrometry—Continued Abstract ———————————————————————— 1 Analytical procedures ———————————— 19 Introduction —————————————————————— 1 Direct —————————————————— 19 Purpose——————————————————————— 2 Chelation-extraction —————————— 19 Scope ——————————————————————— 2 Standard additions ——————————— 20 Definitions ———————————————————— 4 Interferences —————————————————— 21 Significant figures ———————————————— 5 lonization effects ———————————— 21 References ————————————————————— 6 Chemical effects ————————————— 21 Quality control ————————————————————— 7 Matrix effects —————————————— 22 Accuracy of analysis —————————————— 7 Spectral-line effects ——————————— 22 Basic laboratory and field requirements ——— 7 Background absorption ———————— 22 Chemical ionic balance —————————————— 7 Automation techniques ——————————— 23 Relation of residue on evaporation to calculated References ——————————————————— 23 dissolved solids ———————————————— 9 Atomic emission spectrometry ————————— 24 Relation of specific conductance to residue on Principles ——————————————————— 24 evaporation —————————————————— 9 Emission phenomenon ————————— 24 Precision of analysis ——————————————— 9 Quantitative analysis by emission —— 24 Reference material ——————————————— 10 Types of excitation sources ———————— 25 The central laboratories —————————————— 11 Flames ——————————————————— 25 Use and documentation of standard laboratory Direct-current arc ———————————— 26 procedures ————————————————— 11 Alternating-current spark ——————— 26 Analytical review procedures ———————— 12 Direct-current argon plasma (plasma References ———————————————————— 12 jet) ———————————————————— 27 Laboratory equipment and techniques ——————— 13 Inductively-coupled argon radiofrequency Glassware and other containers ————————— 13 plasma torch —————————————— 27 Chemicals and solutions ————————————— 13 References ——————————————————— 28 Purity —————————————————————— 13 Colorimetry ————————————————————— 28 Standard solutions —————————————— 14 Basic principles ——————————————— 28 Nonstandard solutions ——————————— 14 Instrumental principles ——————————— 29 Accuracy of measurement ————————— 14 Analytical procedures ———————————— 29 References ———————————————————— 14 Interferences ————————————————— 30 Analytical techniques ————————————————— 15 Automated analyses ————————————— 31 Gravimetry ———————————————————— 15 References —————————————————— 32 Principles —————————————————— 15 Electrometry ——————————————————— 33 Analytical balance —————————————— 15 Voltammetry ————————————————— 33 Accuracy ———————————————————— 15 Ion-selective electrodes ——————————— 34 Titrimetry ————————————————————— 16 Specific conductance ———————————— 36 Principles ——————————————————— 16 pH ——————————————————————— 37 Standard solutions —————————————— 16 References —————————————————— 38 Factor-weight computations ———————— 16 Ion chromatography ———————————————— 38 Automated titrations ———————————— 16 Principles ——————————————————— 38 Atomic absorption spectrometry ———————— 17 Apparatus —————————————————— 38 Basic principles ——————————————— 17 Pumps —————————————————— 39 Instrumental principles ——————————— 17 Sample-injection systems ———————— 39 Radiant energy source ————————— 17 Separator resins ———————————— 40 Sample chamber ———————————— 18 Suppressor resins ———————————— 40 Wavelength selector ——————————— 19 Detectors ————————————————— 42 Detector —————————————————— 19 Automation ———————————————— 43 Information processing ————————— 19 References ——————————————————— 43

VII VIII CONTENTS

Page Page Sample preparation and pretreatment ——————— 45 Analytical methods—Continued Sample preparation, bottom-material —————— 45 Calcium, total-in-sediment, atomic absorption spec­ Subsampling, bottom-material, coring ————— 46 trometric, direct ———————————————— 145 Subsampling, bottom-material, splitting ———— 47 Carbon dioxide, calculation ——————————— 147 Percent moisture, total-in-bottom-material, Chloride, colorimetric, ferric thiocyanate ——— 149 gravimetric ———————————————————— 48 Chloride, colorimetric, ferric thiocyanate, Extraction procedure, bottom-material ———— 48 automated-segmented flow —————————— 151 Extraction procedure, water-suspended sediment 50 Chloride, colorimetric, ferric thiocyanate, auto­ Total decomposition, sediment ————————— 51 mated-discrete ————————————————— 155 Analytical methods ——————————————————— 53 Chloride, titrimetric, mercurimetric —————— 157 Acidity, electrometric titration ————————— 53 Chloride, titrimetric, Mohr ——————————— 159 Alkalinity, electrometric titration ———————— 55 Chloride, ion-exchange chromatographic, auto­ Alkalinity, electrometric titration, automated - 57 mated —————————————————————— 161 Aluminum, atomic emission spectrometric, d-c Chromium, atomic absorption spectrometric, plasma —————————————————————— 59 chelation-extraction —————————————— 163 Aluminum, atomic absorption spectrometric, Chromium, atomic absorption spectrometric, direct 167 chelation-extraction——————————————— 61 Chromium, atomic absorption spectrometric, Aluminum, atomic absorption spectrometric, graphite furnace ———————————————— 169 direct —————————————————————— 63 Chromium, total-in-sediment, atomic absorption Aluminum, total-in-sediment, atomic absorption spectrometric, direct —————————————— 173 spectrometric, direct —————————————— 65 Chromium, hexavalent, atomic absorption spec­ Antimony, atomic absorption spectrometric, trometric, chelation-extraction ——————— 175 hydride ————————————————————— 67 Chromium, hexavalent, colorimetric, diphenylcar- Antimony, total-in-sediment, atomic absorption oaziQe *"•——~~—™———————_—————————————-.—— iff spectrometric, hydride ———————————— 71 Cobalt, atomic absorption spectrometric, chelation- Arsenic, atomic absorption spectrometric, hydride 73 extraction ——————————————————— 179 Arsenic, atomic absorption spectrometric, hydride, Cobalt, atomic absorption spectrometric, direct 181 automated ——————————————————— 77 Cobalt, atomic absorption spectrometric, graphite Arsenic, colorimetric, silver diethyldithiocarbamate 83 furnace ————————————————————— 183 Arsenic, total-in-sediment, atomic absorption spec­ Cobalt, atomic emission spectrometric, ICP — 187 trometric, hydride ——————————————— 87 Cobalt, total-in-sediment, atomic absorption spec­ Barium, atomic absorption spectrometric, direct 89 trometric, direct ————————————————— 189 Barium, atomic emission spectrometric, ICP — 91 Color, electrometric, visual comparison ———— 191 Beryllium, atomic absorption spectrometric, Copper, atomic absorption spectrometric, chelation- direct —————————————————————— 93 extraction ———————————————————— 193 Beryllium, atomic emission spectrometric, ICP 95 Copper, atomic absorption spectrometric, direct 195 Boron, atomic emission spectrometric, d-c plasma 97 Copper, atomic absorption spectrometric, graphite Boron, colorimetric, azomethine H, automated- furnace —————————————————————— 197 segmented flow ————————————————— 99 Copper, atomic emission spectrometric, ICP — 201 Boron, colorimetric, curcumin ————————— 103 Copper, total-in-sediment, atomic absorption spec­ Boron, colorimetric, dianthrimide ——————— 107 trometric, direct ——————————————— 203 Bromide, titrimetric, hypochlorite oxidation —— 111 Cyanide, colorimetric, barbituric acid, automated- Bromide, ion-exchange chromatographic, auto- ~~ segmented flow ————————————————— 205 mated ————————————————————— 115 Cyanide, colorimetric, pyridine-pyrazolone —— 209 Bromide, ion-exchange chromatographic-electro- Density, gravimetric ——————————————— 213 chemical, automated ————————————— 117 Fluoride, colorimetric, zirconium-eriochrome Bromide, colorimetric, fluorescein, automated* cyanine R ———————————————————— 215 segmented flow ————————————————— 121 Fluoride, electrometric, ion-selective electrode - 219 Cadmium, atomic absorption spectrometric, Fluoride, electrometric, ion-selective electrode, chelation-extraction —————————————— 125 automated-segmented flow ————————— 221 Cadmium, atomic absorption spectrometric, direct 127 Fluoride, ion-exchange chromatographic, Cadmium, atomic absorption spectrometric, automated ——————————————————— 225 graphite furnace ———————————————— 129 Hardness, calculation —————————————— 227 Cadmium, atomic emission spectrometric, ICP 133 Hardness, titrimetric, complexometric ————— 229 Cadmium, total-in-sediment, atomic absorption Hardness, noncarbonate, calculation ————— 231 spectrometric, direct —————————————— 135 Iodide, colorimetric, ceric-arsenious oxidation - 233 Calcium, atomic absorption spectrometric, direct 137 Iodide, colorimetric, ceric-arsenious oxidation, Calcium, atomic absorption spectrometric, direct- automated-segmented flow ————————— 235 EPA ——————————————————————— 141 Iodide, titrimetric, bromine oxidation ————— 237 Calcium, atomic emission spectrometric, ICP — 143 Iron, atomic absorption spectrometric, direct — 239 CONTENTS IX

Page Page Analytical methods—Continued Analytical methods—Continued Iron, atomic emission spectrometric, ICP ——— 241 Nitrogen, ammonia plus organic, colorimetric, Iron, total-in-sediment, atomic absorption spec­ block digestor-salicylate-hypochlorite, trometric, direct ———————————————— 243 automated-discrete —————————————— 331 Lead, atomic absorption spectrometric, chelation- Nitrogen, ammonia plus organic, colorimetric, extraction ———————————————————— 245 digestion-distillation-nesslerization —————— 335 Lead, atomic absorption spectrometric, direct - 247 Nitrogen, ammonia plus organic, titrimetric, Lead, atomic absorption spectrometric, graphite digestion-distillation —————————————— 337 furnace —————————————————————— 249 Nitrogen, nitrate, ion-exchange chromatographic, Lead, atomic emission spectrometric, ICP —— 253 automated ——————————————————— 339 Lead, total-in-sediment, atomic absorption spec­ Nitrogen, nitrite, colorimetric, diazotization — 341 trometric, direct ———————————————— 255 Nitrogen, nitrite, colorimetric, diazotization, Lithium, atomic absorption spectrometric, direct 257 automated-segmented flow —————————— 343 Lithium, atomic emission spectrometric, ICP — 259 Nitrogen, nitrite, colorimetric, diazotization, Lithium, total-in sediment, atomic absorption spec­ automated-discrete —————————————— 347 trometric, direct ——————————————— 261 Nitrogen, nitrite, ion-exchange chromatographic, Magnesium, atomic absorption spectrometric, automated ——————————————————— 349 direct ——————————————————————— 263 Nitrogen, nitrite plus nitrate, colorimetric, cad­ Magnesium, atomic absorption spectrometric, mium reduction-diazotization, automated- direct-EPA ———————————————————— 267 segmented flow ————————————————— 351 Magnesium, atomic emission spectrometric, ICP 269 Nitrogen, nitrite plus nitrate, colorimetric, hydra- Magnesium, total-in-sediment, atomic absorption zine reduction-diazotization, automated-discrete 355 spectrometric, direct ————————————— 271 Oxygen demand, chemical (COD}, colorimetric, Manganese, atomic absorption spectrometric, dichromate oxidation ————————————— 357 chelation-extraction ————————————— 273 Oxygen demand, chemical (COD), titrimetric, di­ Manganese, atomic absorption spectrometric, chromate oxidation —————————————— 359 direct ————————————————————— 275 pH, electrometric, glass-electrode ——————— 363 Manganese, atomic absorption spectrometric, Phosphorus, colorimetric, phosphomolybdate — 365 graphite furnace ————————————————— 277 Phosphorus, colorimetric, phosphomolybdate, Manganese, atomic emission spectrometric, ICP 281 automated-segmented flow —————————— 367 Manganese, total-in-sediment, atomic absorption Phosphorus, colorimetric, phosphomolybdate, spectrometric, direct —————————————— 283 automated-discrete —————————————— 371 Mercury, atomic absorption spectrometric, Phosphorus, orthophosphate plus hydrolyzable, col­ flameless ———————————————————— 285 orimetric, phosphomolybdate ———————— 375 Mercury, atomic absorption spectrometric, Phosphorus, orthophosphate plus hydrolyzable, col­ flameless automated-sequential ———————— 289 orimetric, phosphomolybdate, automated- Molybdenum, atomic absorption spectrometric, segmented flow ————————————————— 377 chelation-extraction —————————————— 293 Phosphorus, orthophosphate, colorimetric, phos­ Molybdenum, atomic emission spectrometric, phomolybdate —————————————————— 381 ICP ————————————-——————————— 297 Phosphorus, orthophosphate, colorimetric, Nickel, atomic absorption spectrometric, chelation- phosphomolybdate, automated-segmented extraction —————————————————— 299 flow ——————————————————————— 383 Nickel, atomic absorption spectrometric, direct 303 Phosphorus, orthophosphate, colorimetric, phos­ Nickel, atomic absorption spectrometric, graphite phomolybdate, automated-discrete —————— 387 furnace —————————————————————— 305 Phosphorus, orthophosphate, ion-exchange Nickel, total-in-sediment, atomic absorption spec­ chromatographic, automated ————————— 389 trometric, direct ————————————————— 309 Phosphorus, hydrolyzable and organic, calculation 391 Nitrogen, titrimetric, digestion-distillation —— 311 Potassium, atomic absorption spectrometric, Nitrogen, ammonia, colorimetric, distillation- direct —————————————————————— 393 nesslerization —————————————————— 313 Potassium, atomic absorption spectrometric, Nitrogen, ammonia, colorimetric, salicylate- direct-EPA ——————————————————— 395 hypochlorite automated-segmented flow —— 315 Potassium, total-in-sediment, atomic absorption Nitrogen, ammonia, colorimetric, salicylate- spectrometric, direct —————————————— 397 hypochlorite automated-discrete ——————— 319 Selenium, atomic absorption spectrometric, hydride 399 Nitrogen, ammonia, colorimetric, indophenol, Selenium, atomic absorption spectrometric, automated-segmented flow —————————— 321 hydride, automated —————————————— 403 Nitrogen, ammonia, electrometric, ion-selective Selenium, total-in-sediment, atomic absorption electrode ——————————————————————— 325 spectrometric, hydride ————————————— 409 Nitrogen, ammonia plus organic, colorimetric, Silica, atomic absorption spectrometric, direct - 411 block digestor-salicylate-hypochlorite, Silica, atomic emission spectrometric, ICP —— 413 automated-segmented flow —————————— 327 Silica, colorimetric, molybdate blue ——————— 415 CONTENTS

Page Page Analytical methods—Continued Analytical methods—Continued Silica, colorimetric, molybdate blue, automated- Strontium, total-in-sediment, atomic absorption segmented flow ———————————————— 417 spectrometric, direct —————————————— 471 Silica, total-in-sediment, atomic absorption spec­ Sulfate, dissolved, colorimetric, complexometric, trometric, direct ————————————————— 421 methyl-thymol blue, automated-segmented flow 473 Silver, atomic absorption spectrometric, chelation- Sulfate, turbidimetric, barium sulfate, automated- extraction ——————————————————— 423 discrete ————————————————————— 477 Sodium, atomic absorption spectrometric, direct 425 Sulfate, ion-exchange chromatographic, automated 479 Sodium, atomic absorption spectrometric, direct- Sulfate, titrimetric, thorin ———————————— 481 EPA ———————————————————————— 427 Sulfide, titrimetric, iodometric ————————— 483 Sodium, atomic emission spectrometric, ICP — 429 Thallium, atomic absorption, spectrometric, Sodium, total-in-sediment, atomic absorption spec­ graphite furnace ———————————————— 485 trometric, direct ———————————————— 431 Tin, atomic absorption spectrometric, hydride, Sodium absorption ratio, calculation —————— 433 automated ——————————————————— 489 Sodium, percent, calculation —————————— 435 Titanium, total-in-sediment, atomic absorption Solids, residue on evaporation at 180 °C, dissolved, spectrometric, direct —————————————— 495 gravimetric ——————————————————— 437 Turbidity, nephelometric ————————————— 497 Solids, residue on evaporation at 105 °C, dissolved, Vanadium, colorimetric, catalytic oxidation — 499 gravimetric ——————————————————— 439 Vanadium, colorimetric, catalytic oxidation, Solids, residue on evaporation at 105°C, total, automated-segmented flow —————————— 501 gravimetric ——————————————————— 441 Vanadium, atomic emission spectrometric, ICP 505 Solids, residue at 105 °C, suspended, gravimetric 443 Zinc, atomic absorption spectrometric, direct — 507 Solids, volatile-on-ignition, dissolved, gravimetric 445 Zinc, atomic absorption spectrometric, graphite Solids, volatile-on-ignition, total, gravimetric — 447 rum ace —————————.—__«.—•._—______Qyy Solids, volatile-on-ignition, suspended, gravimetric 449 Zinc, atomic emission spectrometric, ICP ——— 513 Solids, volatile-on-ignition, total-in-bottom- Zinc, total-in-sediment, atomic absorption spec­ material, gravimetric —————————————— 451 trometric, direct ———————————————— 515 Solids, nonvolatile-on-ignition, dissolved, calcula­ Metals, atomic emission spectrometric, ICP — 517 tion ———————————————————————— 453 Anions, ion-exchange chromatographic, auto­ Solids, nonvolatile-on-ignition, total, calculation 455 mated ——————————————————————— 523 Solids, nonvolatile-on-ignition, suspended, calcula­ Anions, ion-exchange chromatographic, low ionic- tion ——————————————————————— 457 strength water, automated ———————————— 527 Solids, sum of constituents, calculation ———— 459 Metals, major, total-in-sediment, atomic absorption Specific conductance, electrometric, Wheatstone spectrometric, direct ————————————— 531 bridge —————————————————————— 461 Metals, major and minor, total-in-sediment, atomic Strontium, atomic absorption spectrometric, absorption spectrometric, direct ——————— 535 direct ——————————————————————— 465 Metals, minor, total-in-sediment, atomic absorption Strontium, atomic emission spectrometric, ICP 469 spectrometric, hydride ———————————— 541

FIGURES

Page i. Example of standard-addition method —————————————————————————————————————————— 21 2. Energy level diagram ————————————————————————————————————————————————— 24 3. Schematic of the nebulization, desolvation, atomization, and excitation processes 25 4. Plasma torch configuration ——————————• 28 5. Ion chromatography system for anions ———- 39 6. A typical chromatogram for seven anions —— 39 7. Ion chromatographic schematic diagram ———• 40 8. Fiber suppressor ————————————————• 41 9. Plasma position on entrance slit for aluminum • 59 10. Stibine vapor analyzer ——————————————• 68 11. Arsine vapor analyzer ———————— 74 CONTENTS XI

Page 12. Stripping-condensing column and quartz-tube furnace ——————————————————————————————— 78 13. Arsenic, acid-persulfate manifold —————————————————————————————————————————— 79 14. Arsenic, ultraviolet radiation manifold ———————————————————————————————————————— 80 15. Arsine generator, scrubber, and absorber ——————————————————————————————————————— 84 16. Plasma position on entrance slit for boron —————————————————————————————————————— 98 17. Boron, azomethine H manifold ———————————————————————————————————————————— 100 18. Bromide, fluorescein manifold —————————————————————————————————————————————— 122 19. Calcium manifold ————————————————————————————————————————————————————— 137 20. Chloride, ferric thiocyanate manifold —————————————————————————————————————————— 152 21. Cyanide, distillation train ———————————————————————————————————————————————— 206 22. Cyanide, barbituric acid manifold ———————————————————————————————————————————— 208 23. Cyanide, distillation train ———————————————————————————————————————————————— 210 24. Fluoride, distillation assembly ————————————————————————————————————————————— 216 25. Fluoride, distillation assembly ———————————————————————————————————————————— 222 26. Fluoride, ion-selective electrode manifold ————————————————————————————————————— 223 27. Iodide, ceric-arsenious oxidation manifold ————————————————————————————————————— 236 28. Magnesium manifold ——————————————————————————————————————————————————— 264 29. Absorption cell and aerator ——————————————————————————————————————————————— 286 30. Mercury manifold ——————————————————————————————————————————————————— 290 31. Vapor-liquid separator ———————————————————————————————————————————————— 290 32. Nitrogen, ammonia, salicylate-hypochlorite manifold ——————————————————————————————— 317 33. Nitrogen, ammonia, indophenol manifold ————————————————————————————————————— 323 34. Nitrogen, ammonia plus organic, salicylate-hypochlorite manifold ———————————————————————— 329 35. Nitrogen, nitrite, diazotization manifold ———————————————————————————————————————— 344 36. Nitrogen, nitrite plus nitrate, cadmium reduction-diazotization, manifold ——————————————————— 353 37. Phosphorus, phosphomolybdate manifold ——————————————————————————————————————— 369 38. Phosphorus, phosphomolybdate manifold ————————————————————————————————————— 379 39. Phosphorus, phosphomolybdate manifold ————————————————————————————————————— 384 40. Selenium hydride vapor analyzer ———————————————————————————————————————————— 400 41. Stripping-condensing column and quartz-tube furnace ——————————————————————————————— 404 42. Selenium, hydride manifold —————————————————————————————————————————————— 405 43. Silica, molybdate manifold ———————————————————————————————————————————————— 418 44. Strontium manifold —————————————————————————————————————————————————— 466 45. Sulfate, methylthymol blue manifold, low range, 5 to 100 mg/L SO4 —————————————————————— 474 46. Sulfate, methylthymol blue manifold, high range, 100 to 300 mg/L SO4 ————————————————————— 475 47. Cation-exchange column for sulfate —————————————————————————————————————————— 481 48. Stripping-condensing column and quartz tube furnace ——————————————————————————————— 490 49. Tin, hydride manifold ———————————————————————————————————————————————————— 491 50. Vanadium, catalytic oxidation manifold ———————————————————————————————————————— 502 51. Block diagram of spectrometer system ——————————————————————————————————————— 518 52. Quartz torch ————————————————————————————————————————————————————————— 518 53. Pump system ———————————————————————————————————————————————————————— 519

TABLES

Page 1. Factors for converting milligrams per liter to milliequivalents per liter ————————————————————— 6 2. Hydrogen ion concentrations as approximated from observed pH values ———————————————————— 8 3. Percent orthophosphate mixtures as related to pH ———————————————————————————————— 8 4. Temperatures of premised flames ————————————————————————————————————————————— 22 5. Recovery of bromide in the presence of chloride for 0.01 to 0.09 mg/L Br ——————————————————— 118 6. Recovery of bromide in the presence of chloride for 0.01 to 0.09 mg/L Br ———————————————————— 118 7. Values of 1.60X1016'0 ' *»H> ———————————————————————————————————————————————— 148 XII CONTENTS

Page 8. Working ranges of constituents for ICP ———————————————————————————————————————— 518 9. Single operator data for ICP ——————————————————————————————————————————————— 522 10. Intel-laboratory precision data for ICP ———————————————————————————————————————— 522 11. Working ranges of anions by ion chromatography —————————————————————————————————— 523 12. Approximate retention times of anions by ion chromatography ————————————————————————— 526 13. Precision for ion chromatographic determination of anions ——————————————————————————— 526 14. Analytical ranges used in the determinations of the six anions ————————————————————————— 527 15. Approximate retention times of anions ——————————————————————————————————————— 529 16. Precision and bias for ion chromatography on simulated precipitation samples ———————————————— 530 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES IN WATER AND FLUVIAL SEDIMENTS

By Marvin J. Fishman and Linda C. Friedman, editors

Abstract The U.S. Geological Survey's responsibility for water appraisal includes not only assessments Chapter Al of the laboratory manual contains methods of the location, quantity, and availability of used by the U.S. Geological Survey to analyze samples of water, but also determinations of water quali­ water, suspended sediments, and bottom material for their content of inorganic constituents. Included are methods for ty. Inherent in this responsibility is the need for determining the concentration of dissolved constituents in extensive water-quality studies related to the water, the total recoverable and total of constituents in physical, chemical, and biological adequacy of water-suspended sediment samples, and the recoverable and natural and developed surface- and ground- total concentrations of constituents in samples of bottom material. The introduction to the manual includes essential water supplies. Included, also, is a need for sup­ definitions and a brief discussion of the use of significant porting research to increase the effectiveness of figures in calculating and reporting analytical results. Quali­ these studies. ty control in the water-analysis laboratory is discussed, in­ As part of its mission the U.S. Geological cluding the accuracy and precision of analyses, the use of Survey is responsible for generating a large part standard-reference water samples, and the operation of an effective quality-assurance program. Methods for sample of the water-quality data for rivers, lakes, and preparation and pretreatment are given also. ground water that is used by planners, develop­ A brief discussion of the principles of the analytical tech­ ers, water-quality managers, and pollution- niques involved and their particular application to water and control agencies. A high degree of reliability and sediment analysis is presented. The analytical methods of standardization of these data is paramount. these techniques are arranged alphabetically by constituent. For each method, the general topics covered are the applica­ This chapter is one of a series that documents tion, the principle of the method, the interferences, the ap­ and makes available data-collection and analysis paratus and reagents required, a detailed description of the procedures used by the U.S. Geological Survey. analytical procedure, reporting results, units and significant The series describes procedures for planning and figures, and analytical precision data, when available. More executing specialized work in water-resources in­ than 125 methods are given for the determination of 70 in­ organic constituents and physical properties of water, vestigations. The unit of publication, the chapter, suspended sediment, and bottom material. is limited to a narrow field of subject matter. This format permits flexibility in revision and publica­ tion as necessary. For convenience the chapters Introduction on methods for water-quality analysis are grouped into the following categories: The Department of the Interior has a basic Inorganic substances responsibility for the appraisal, conservation, Minor elements by emission spectroscopy and efficient utilization of the Nation's natural Organic substances resources. As one of severed Interior agencies, Aquatic biological and microbiological the U.S. Geological Survey's primary function samples in relation to water is to assess its availability Radioactive substances and utility as a national resource for all uses. Quality assurance 1 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Provisional drafts of new or revised analytical Scope methods are distributed to field offices of the U.S. Geological Survey for their use. These This manual includes techniques and pro­ drafts are subject to revision based on use or be­ cedures suitable for the analysis of represent­ cause of advancement in knowledge, techniques, ative samples of water and fluvial sediments. or equipment. After a method is sufficiently The methods and techniques include: developed and confirmed, it is incorporated in Gravimetry a supplement to the chapter or in a new edi­ Titrimetry tion of the chapter and is then available from Atomic absorption spectrometry the Superintendent of Documents, U.S. Gov­ Atomic emission spectrometry ernment Printing Office, Washington, D.C. Colorimetry 20402. Electrometry Ion-exchange chromatography Sample preparation and pretreatment Purpose Calculation methods Rapid changes in technology are constantly For each method, the general topics covered providing new and improved methods for the are application, principle of the method, inter­ study of water-quality characteristics. There­ ferences, apparatus and reagents required, a fore, methods manuals must be updated fre­ detailed description of the analytical procedure, quently in order to gain the advantages of reporting results, units and significant figures, and analytical precision data, when available. improved technology. The purpose of this chap­ ter is to record and disseminate methods used Each method, where applicable, applies to the determination of constituents in solution (dis­ by the U.S. Geological Survey to analyze sam­ solved), the determination of total or total ples of water, suspended sediment, and bottom recoverable constituents (substances both in material collected in water-quality investiga­ solution and adsorbed on or a part of suspended tions. This chapter is an update of Techniques sediment), and finally the determination of total of Water-Resources Investigation (TWRI) of or recoverable constituents from samples of bot­ the U.S. Geological Survey, book 5, chapter Al, tom material. " Methods for determination of inorganic This chapter includes methods for determin­ substances in water and fluvial sediments," by ing the following constituents and physical Skougstad and others, published in 1979 and of properties: a supplement published by Fishman and Brad­ ford in 1982. Dissolved constituents and physical properties Although excellent and authoritative manu­ als on water analysis are available (American Acidity Carbon- Public Health Association and others, 1980; Alkalinity dioxide American Society for Testing and Materials, Chloride 1978,1984), most of them emphasize primarily Aluminum Chromium either municipal, industrial, or agricultural Antimony Chromium(VI) water utilization. No single reference or com­ Arsenic Cobalt bination meets all requirements as a guide to Copper the broader phases of water-quality investiga­ Barium Cyanide tions conducted by the U.S. Geological Survey. Beryllium Fluoride These investigations are intended to define the Boron chemical, physical, and biological character­ Hardness istics of the Nation's surface- and ground-water Bromide Hardness, resources, as well as to indicate the suitabil­ Cadmium non-car­ ity of these resources for various beneficial bonate uses. Calcium Iodide METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 3 Dissolved constituents and physical Total constituents and physical properties properties—Continued Antimony Phosphorus Iron Phosphorus, hydrolyzable Arsenic Phosporus, orthophosphate Lead plus organic plus hydrolyzable Lithium Potassium Cyanide Phosphorus, orthophosphate Magnesium Selenium Density Phosphorus, hydrolyzable Manganese Silica plus organic Mercury Saver Fluoride Selenium Molybdenum Sodium Nitrogen, Solids, nonvolatile-on- Nickel Sodium adsorption ratio ammonia ignition Nitrogen, Sodium, percent Nitrogen, am­ Solids, residue on evapora­ ammonia Solids, sum of constituents monia plus tion at 105°C Nitrogen, Solids, nonvolatile-on- organic ammonia plus ignition Nitrogen, Solids, volatile-on-ignition organic Solids, volatile-on-ignition nitrite Nitrogen, nitrate Solids, residue on evapora­ Nitrogen, Sulfide Nitrogen, nitrite tion at 105°C nitrite plus Nitrogen, nitrite Solids, residue on evapora­ nitrate plus nitrate tion, at 180°C Oxygen TUrbidity pH Specific conductance demand, Phosphorus Strontium chemical Phosphorus, Sulfate orthophosphate Thallium Constituents recoverable from bottom material plus hydrolyzableTin Phosphorus, Vanadium Aluminum Lithium orthophosphate Zinc Barium Magnesium Beryllium Manganese Suspended constituents Boron Mercury Solids, Solids, suspended, Cadmium Molybdenum nonvolatile- residue at 105 °C Calcium Nickel on-ignition Chromium Potassium Solids, Cobalt Sodium volatile-on- Copper Strontium ignition Iron Zinc Lead Total recoverable constituents and physical property Tbtal constituents in suspended or bottom material Aluminum Lithium Barium Magnesium Aluminum Cyanide Beryllium Manganese Antimony Iron Boron Mercury Arsenic Lead Cadmium Molybdenum Boron Lithium Calcium Nickel Magnesium Chromium Potassium Cadmium Manganese Cobalt Silver Nickel Color Sodium Calcium Nitrogen Copper Strontium Chromium Nitrogen, ammonia Iron Tin Cobalt Nitrogen, ammonia plus Lead Zinc Copper organic TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Total constituents in Suspended or bottom Definitions material—continued Reporting the results of analyses of water and Nitrogen, nitrite Silica fluvial sediment samples requires the use of plus nitrate Sodium several terms that are based on the combina­ Oxygen demand, Solids, volatile on ignition tion of physical phases sampled (water or sedi­ chemical Strontium ments) and the analytical methods used. These Phosphorus Titanium terms are defined below. Potassium Zinc Dissolved.—Pertains to the constituents in a Selenium representative water sample that pass through Each method is identified by one or more four- a 0.45-/xm membrane filter. The "dissolved" con­ digit numbers preceded by a letter. The letter stituents are determined from subsamples of prefix designates whether the method applies the filtrate. This convenient operational defini­ to a physical characteristic (P), an inorganic tion is used by Federal agencies that collect substance (I), an organic substance (O), a radio­ water data. active substance (R), a biological characteristic Suspended, recoverable.—Pertains to the con­ or determination (B), an element determined by stituents in a representative water sample that emission spectrographic method (E), or a sedi­ are retained on a 0.45-^m membrane filter and ment characteristic (S), The first digit of the that are brought into solution by digestion identifying number indicates the type of deter­ (usually by using a dilute acid solution). Com­ mination (or procedure) for which the method plete dissolution of all the participate matter is is suitable, according to the following: often not achieved by the digestion treatment, and thus the determination may represent less 0—————Sample preparation. than the "total" amount (that is, less than 95 1—————Manual method for dissolved percent) of the constituent in the sample. To constituents. achieve comparability of analytical data, equiv­ 2—————Automated method for dissolved alent digestion procedures would be required of constituents. all laboratories performing such analyses, 3—————Manual method for analyzing because different digestion procedures are likely water-suspended sediment mixtures. to produce different analytical results. 4—————Automated method for analyzing Determinations of "suspended, recoverable" water-suspended sediment mixtures. constituents are made either by analyzing por­ 5—————Manual method for analyzing tions of the material collected on the filter or, samples of bottom material. more commonly, by calculating the difference 6—————Automated method for analyz­ between the dissolved and the total recoverable ing samples of bottom material. concentrations of the constituent. 7—————Method for suspended consti­ Suspended, toted.—Pertains to the constituents tuents. in a representative water sample that are re­ tained on a (X45-/on membrane filter. This term The last three digits are unique to each method. is used only when the analytical procedure Additionally, each method number has an ap­ assures measurement of at least 95 percent of pended two-digit number designating the year the constituent determined. A knowledge of the of last approval of that method. If revisions of expected form of the constituent in the sample, a method are issued within the calendar year of as well as of the analytical methodology used, last approval, suffixes A, B, and so forth are is required to determine when the results should added to the year designation to identify such be reported as "suspended, total." a subsequent revision. This numbering system Determinations of "suspended, total" consti­ simplifies the identification of each method and tuents are made either by analyzing portions of the updating of the chapter as new or revised the material collected on the filter or, more com­ methods are introduced. monly, by calculating the difference between the METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES dissolved and the total concentrations of the A knowledge of the expected form of the con­ constituent. stituents in the sample, as well as of the ana­ Total, recoverable.—Pertains to the consti­ lytical methodology used, is required to judge tuents in solution after a representative water- when the results should be reported as "total suspended sediment sample is digested (usually in bottom material." by using a dilute acid solution). Complete dis­ A description of an analytical method must solution of all particulate matter is often not compare the result obtained by the method with achieved by the digestion treatment, and thus the value that is sought, which is usually the the determination may represent less than the true concentration of the chemical substance in "total" amount (that is, less than 95 percent) the sample. Definitions of terms that are used of the constituent in the dissolved and sus­ for this purpose are given below. pended phases of the sample. To achieve com­ Accuracy.—A measure of the degree of confor­ parability of analytical data, equivalent mity of the values generated by a specific digestion procedures would be required of all method or procedure with the true value. The laboratories performing such analyses, because concept of accuracy includes both bias (syste­ different digestion procedures are likely to pro­ matic error) and precision (random error). duce different analytical results. Bias.—A persistent positive or negative devia­ Total.—Pertains to the constituents in a repre­ tion of the values generated by a specific sentative water-suspended sediment sample, method or procedure from the true value, ex­ regardless of the constituent's physical or chem­ pressed as the difference between the true value ical form. This term is used only when the ana­ and the mean value obtained by repetitive lytical procedure assures measurement of at testing of the homogeneous sample. least 95 percent of the constituent in both the Limit of detection.—The minimum concentra­ dissolved and the suspended phases of the sam­ tion of a substance that can be identified, meas­ ple. A knowledge of the expected form of the ured, reported with 99-percent confidence that constituent in the sample, as well as of the ana­ the analyte concentration is greater than zero, lytical methodology used, is required to judge and determined from analysis of a sample in a when the results should be reported as "total." given matrix containing analyte. (Note that the word "total" indicates both that Precision.—The degree of agreement of re­ the sample consists of a water-suspended sedi­ peated measurements by a specific method or ment mixture and that the analytical method procedure, expressed in terms of dispersion of determines all of the constituent in the sample). the values generated about the mean value ob­ Recoverable from bottom material.—Pertains to tained by repetitive testing of a homogeneous the constituents in solution after a represent­ sample. ative sample of bottom material is digested (usually using an acid or mixture of acids). Com­ plete dissolution of all bottom material is often Significant figures not achieved by the digestion treatment, and thus the determination may represent less than The significant figures used by the U.S. the total amount (that is, less than 95 percent) Geological Survey in reporting the results of of the constituent in the sample. To achieve analysis in milligrams or micrograms per liter comparability of analytical data, equivalent represent a compromise between the desire to digestion procedures would be required of all achieve both precision of measurement and a laboratories performing such analyses, because degree of uniformity in tabulations of analytical different digestion procedures are likely to pro­ data. A common method used to express the duce different analytical results. precision of a determination is to include all Total in bottom material.—Pertains to the con­ digits known with certainty and the first (and stituents in a representative sample of bottom only the first) doubtful digit. This method has material. This term is used only when the ana­ one obvious disadvantage: published data so lytical procedure assures measurement of at reported may not be interpreted to mean the least 95 percent of the constituent determined. same thing by all users of the data. TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Table 1.—Factors for converting milligrams per liter to milliequivalents per liter [1975 atomic weights]

Sum of atomic Conversion Sum of atomic Conversion Ion weights factor Ion weights factor Ag + 1 107.868 0.00927 1-1 126.9045 0.00788 AI + 3 26.9815 .11119 K + 1 39.0983 .02558 As + 3 74.9216 .04004 Li + 1 6.941 .14407 AsO*3 138.9192 .02160 Mg+2 24.305 .08229 Ba+2 137.33 .01456 Mn+2 54.9380 .03640 Be + 2 9.01218 .22192 Mn + 4 54.9380 .07281 BOg3 58.8082 .05101 Mo+3 95.94 .03127 Br-1 79.904 .01252 Na+ 1 22.9898 .04350 Ca + 2 40.08 .04990 NH4+1 18.0383 .05544 Cd+2 112.41 .01779 Ni + 2 58.70 .03407 CM 35.453 .02821 NOa"1 46.0055 .02174 CO + 2 58,9332 .03394 NO^1 62.0049 .01613 C052 60.0092 .03333 OH-' 17.0073 .05880 Cr+3 51.996 .05770 Pb+2 207.2 .00965 CrO^ 115.9936 .01724 P04-3 94.97136 .03159 CN-1 26.0177 .03844 S-2 32.06 .06238 CU + 2 63.546 .03147 SeO^2 142.9576 .01399 F-1 18.9984 .05264 Sn + 2 118.69 .01685 Fe + 2 55.847 .03581 Sn+4 118.69 .03370 Fe+3 55.847 .05372 30^2 96.0576 .02082 H + 1 1.0079 .99216 Sr+2 87.62 .02283 Hg + 2 200.59 .00997 V + 2 50.9415 .03926 HCO§1 61.0171 .01639 VO + 2 66.9409 .02988 HPO^ 95.97926 .02084 VO§1 98.9397 .01011 H2P04i 96.98716 .01031 Zn + 2 65.38 .03059

Chemical milliequivalents per liter are com­ Federation, 1985, Standard methods for the examina­ puted by multiplying the reported concentration tion of water and wastewater (16th ed.): Washing­ ton, D.C., American Public Health Association, of the individual constituents, in milligrams per 1268 p. liter, by the reciprocal of their equivalent weights. American Society for Testing and Materials, 1978, Manual The factors for the conversion of milligrams per on water (4th ed.}: American Society for Testing and liter to milliequivalents per liter for the more Materials, Special Technical Publication No. 442A, commonly determined constituents are given in 472 p. table 1. American Society for Testing and Materials, 1984, Annual Milliequivalents per liter as reported by the book of ASTM Standards, Section II, Water: Phila­ Geological Survey are numerical expressions of delphia, American Society for Testing and Materials, milligrams per liter and for uniformity are car­ v. 11.01, 750 p. ried to three decimal places regardless of the Skougstad, M. W., Fishman, M. J., Friedman, L. C., Erd- mann, D. E., and Duncan, S. S., 1979, Methods for magnitude of the milligrams-per-liter value; the determination of inorganic substances in water and significant figures shown do not reflect the preci­ fluvial sediments: Techniques of Water-Resources In­ sion of the measurement; the milligrams-per-liter vestigations of the United States Geological Survey, values do reflect that precision. book 5, chapter Al, 626 p. Fishman, M. J., and Bradford, W. L., 1982, A supple­ References ment to methods for the determination of inor­ ganic substances in water and fluvial sediments: American Public Health Association, American Water U.S. Geological Survey Open-File Report 82-272, Works Association, and Water Pollution Control 136 p. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES Quality control

Accuracy of analysis experience in water chemistry must be involved both in performing the analyses and in super­ vising the laboratory. Some errors are practically unavoidable in The use of reference materials, spiked sam­ analytical work. Errors are inherent in the ples, and samples split between laboratories methods or instruments employed, or may arise must constitute at least 15 percent of the work­ from impurities in reagents and even in distilled load for any parameter. The percentage for rare­ or demineralized water. The analyst's skill and ly used methods must be considerably higher. general judgment have a direct bearing on the A data-review program must provide continual accuracy of the analytical statement. After the evaluation of the laboratory's performance. chemical analysis of the water sample has been The analysis of an improperly collected sam­ completed, the validity of the results can be ple is meaningless. To minimize errors and vari­ evaluated by several methods. No one method ation in data due to sampling, field personnel of checking gives conclusive proof of the ac­ must maintain records on sampling, including curacy of the determinations, but the process field measurements. Appropriate field measure­ of checking may reveal some dubious results or ments and information peculiar to the sample some additional constituents of the sample that need to be supplied with the sample to the were not considered in the analysis. laboratory. Samples must be preserved, if re­ In addition, a quality assurance program is quired, and must be shipped without delay in essential to ensure the validity of all analytical bottles and containers appropriate to the deter­ data (Office of Water Planning and Standards, minations. Time-critical determinations need to 1976). A well-designed program must provide be performed within the allowable time either unbiased monitoring of the accuracy and preci­ in the laboratory or in the field. sion of reported data and must also provide Analyses performed in the field must be timely information to the analyst on errors and carefully monitored. Reference materials must potential errors. be used, instruments must be calibrated regu­ Within the laboratory, quality assurance larly prior to going to the field, and personnel should be practiced in all areas and on all levels must be thoroughly trained for field analyses. with at least 10 percent of both dollar and man­ power budgets devoted to quality-control and quality assurance activities. Operationally, a Chemical ionic balance quality assurance program should consist of the standardization of all analytical methods, the One of the most commonly used procedures preparation and use of reference materials, for checking water analyses is the balancing of analysis of replicate samples, and a manual and the chemical equivalents of the major ions. (or) computer-assisted review of the analytical Because water is an electrically neutral system, results. the sum of the milliequivalents of the cations in solution must equal the sum of the milli­ equivalents of the anions. If all of the predomi­ Basic laboratory and nant ions have been determined, the milliequiv­ alents per liter (me/L) of cations and anions field requirements should be in balance. All major ionic species must, of course, be determined and properly Any laboratory performing work for the U.S. identified. Geological Survey, Water Resources Division, The hydrogen-ion content of acid water is in­ must be clean and free from atmospheric con­ cluded in the balance. The hydrogen-ion con­ taminants. Safety features and programs must centration is approximated from the hydrogen- meet State and Federal health and safety ion activity as determined by the pH of the requirements. Personnel with education and sample. TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

pH = log10 Table 3.—Percent orthophosphate mixtures as related to PH or HPO^2 HaPO^ HP042 H2P041 PH (percent) (percent) PH (percent) (percent) where aH+1 is the effective hydrogen-ion con­ 4.5 0.2 99.8 7.3 55.3 44.7 4.6 .2 99.8 7.4 60.9 39.1 centration (hydrogen-ion activity). 4.7 ,3 99.7 7.5 66.0 34.0 The calculated pH of standard solutions of 4.8 .4 99.6 7.6 71.2 28.8 sulfuric acid has been compared with deter­ 4.9 .5 99.5 7.7 75.6 24.4 5.0 .6 99.4 7.8 79.7 20.3 mined pH, and the agreement is good up to 2.0 5.1 .8 99.2 7.9 83.1 16.9 me/L H +1 (pH 2.70). Reproducibility and ac­ 5.2 1.0 99.0 8.0 86,1 13.9 curacy of ± 0.1 me/L H+ 1 is the best that can 5.3 1.2 98.8 8.1 88.7 11.3 5.4 1.5 98.5 8.2 90.7 9.3 be anticipated under normal operating condi­ 5.5 1.9 98.1 8.3 92.5 7.5 tions and with most waters. Considerable error 5.6 2.4 97.6 8.4 93.7 6.3 may be introduced in converting pH to hydro­ 5.7 3.0 97.0 8.5 95.1 4.9 5.8 3.8 96.2 8.6 96.1 3.9 gen-ion concentration because of the effect of 5.9 4.7 95.3 8.7 96.9 3.1 other ions on the activity of the hydrogen ion; 6.0 5.8 94.2 8.8 97.5 2.5 however, this procedure is quite useful in deter­ 6.1 7.2 92.8 8.9 98.0 2.0 6.2 8.9 91.1 9.0 98.4 1.6 mining acidity in low ionic strength water such 6.3 11.0 89.0 9.1 98.7 1.3 as precipitation. See Kolthoff and Laitinen 6.4 13.5 86.5 9.2 99.0 1.0 (1941) and Bates (1964) for a full discussion of 6.5 16.2 83.8 9.3 99.2 .8 6.6 19.8 80.2 9.4 99.4 .6 the subject. 6.7 23.6 76.4 9.5 99.5 .5 Table 2 gives hydrogen ion concentrations ap­ 6.8 28.2 71.8 9.6 99.6 .4 6.9 33.0 67.0 9.7 99.7 .3 proximated from selected pH values. 7.0 38.3 61.7 9.8 99.7 .3 Multivalent ions present difficulties in the 7.1 43.9 56.1 9.9 99.8 .2 ionic balance unless the ionic states are differen­ 7.2 49.5 50.5 10.0 99.8 .2 tiated by the analysis. Orthophosphates may occur in water as PO^3, HPO^2, and HgPO^1; the proportion of each of these ions is related to the pH of the water. The PO^3 ion occurs on­ per liter of alkalinity must be corrected because ly above about pH 10.5. Because natural waters HPC>42 and HgPO^1 will partially titrate as al­ almost never attain this pH, a general assump­ kalinity. Normally, this correction is not nec­ tion can be made that the POj3 ion is not pre­ essary because the concentration of phosphorus sent in natural waters. For the purpose of ionic in water is seldom high enough to affect the balance, the proportion of HPO^2 and I^PO^1 ionic balance. present can be calculated from the pH relation The values in table 3 were computed from the as shown in table 3 for waters having pH values following chemical equilibrium relationships: of 10.0 or less. If HPO^2 and R2PO'4l are in­ cluded in the ionic balance, the milliequivalents HoPOi1 = H+ 1 + HP072

Table 2.—Hydrogen-ion concentrations as approximated [HPOj2] from observed pH values

H + 1 concent rat Ion H + 1 concentration PH (me/L) PH (me/L) 4.25-3.85 0.1 3.05 .9 3.80-3.60 .2 3.00 1.0 3.55-3.50 .3 2.95 1.1 3.45-3.40 .4 2.90 1.3 Kt [HPO;2] 3.35-3.30 .5 2.85 1.4 3.25-3.20 .6 2.80 1.6 3.15 .7 2.75 1.8 where 3.10 .8 2.70 2.0 Kf = 6.2X10-8 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES Other forms of phosphorus cannot be easily Relation of residue on differentiated in this manner. More accurate procedures for the calculation of anionic species evaporation to calculated from pH and for the correction of activities to dissolved solids stoichiometric concentrations are given by Hem (1961,1970), but such methods are not usually Comparison of the residue on evaporation needed for routine water analysis. with the dissolved solids calculated from the Dissociation also must be considered in bal­ analytical statement provides a rough check on ancing analyses. Many of the determinations, the comprehensiveness of an analysis. However, particularly those for the heavy metals, do not the residue-on-evaporation value will be higher differentiate between dissociated and undisso- than the calculated dissolved solids if appreci­ ciated constituents. Constituents that hydro- able amounts of organic or undetermined in­ lyze to give undissociated products that are organic materials are present, or if water of determined with the ionized forms in the anal­ hydration is contained in the residue; the value ysis cannot be included directly in the ionic will be lower if volatile solids are lost during balance. Published dissociation constants give evaporation. The calculated value may appear some indication of the possible ionized concen­ higher if weak acid radicals other than carbo­ tration, but complete confidence cannot be nate and bicarbonate (for example, phosphate, placed in these values when considering com­ borate, and silicate) are included both individ­ plex solutions such as natural water. ually and as part of the alkalinity value. The deviations from ionic balance can be ex­ pressed in terms of absolute quantities or as a percentage of the total ionic concentration. The Relation of specific conductance analyst must use some type of sliding scale to to residue on evaporation evaluate the significance of the deviations for water of different concentrations. For example, For most natural waters of mixed type the normally, the deviation between milliequiva- specific conductance, in microsiemens per centi­ lents per liter of cations and anions will ap­ meter at 25 °C multiplied by a factor of 0.65, proach 2 percent for a sample with a total approximates the residue on evaporation in milligrams per liter. This equation is not an (cations plus anions) milliequivalent-per-liter exact relation because the conductance of a value of 20 and will approach 3 percent for a solution is dependent on the type and total sample with a total milliequivalent-per-liter quantity of ions in solution. More precise rela­ value of 7; however, the deviation may be as tions can be developed for specific water types. high as 12 percent for a sample with a total The specific conductance in microsiemans per milliequivalent-per-liter value of 0.9. centimeter at 25 °C divided by 100 approx­ Chemical balance is an indication of only the imates the milliequivalents per liter of anions gross validity of the analysis. If only chemical- and cations. This relation is particularly helpful balance checks are used, very large errors in the for detecting the location of error (in anions or determination of minor constituents can go cations), as well as for estimating the com­ unnoticed and compensating errors can go un­ prehensiveness of an analysis. detected. Large deviations indicate either a large error in one or more determinations or the presence of some undetermined constituent, but Precision of analysis a good balance is not conclusive evidence that each of the determinations is accurate or that Each analytical procedure in this chapter in­ all constituents have been determined. Chemical cludes a statement, if data are available, indi­ balance is one tool for evaluating the validity cating the precision to be expected for that and comprehensiveness of an analysis, but it procedure. In general, these statements have must not be the only goal of the analyst. been calculated from data obtained through 10 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS multi-laboratory analyses of test samples pre­ however, these same two values are interpreted pared by U.S. Geological Survey laboratories. as significantly different if the analytical preci­ For most procedures, precision data are within sion is ±5 percent. the concentration range specified; however, in some, the data do not cover the entire range, and in a few, the data are all below the lower Reference material range (for example, the determination of cobalt by direct atomic absorption spectrometry). Ref­ Reference materials must be used to monitor erence materials were not available for the lat­ the analyses. Two forms of reference materials ter element. At the other extreme, precision are used for water analyses: ampouled concen­ data for several procedures exceed the upper trates and prepared natural waters. Each type concentration limit and information is not avail­ has certain advantages for quality control. able to determine if the samples were analyzed Ampouled concentrates are obtained from with or without dilution. the U.S. Environmental Protection Agency, The precision is expressed in terms of the per­ National Bureau of Standards, commercial cent relative standard deviation, the ratio of the sources, or are prepared by a Water Resources standard deviation to the mean times 100 per­ Division (U. S. Geological Survey) quality cent. A convenient formula to calculate the assurance support project, which is independent standard deviation is of the laboratories. Most constituents can be prepared as ampouled concentrates. These can later be diluted quantitatively with either dis­ tilled or natural water to provide a variety of OT = matrices and final concentration levels. Such concentrates are particularly useful in method- 71-1 development or method-comparison studies because data can be obtained both on precision where and on percentage recovery. Reference samples with working-level concen­ i = an analysis, trations of stable constituents can be prepared n = number of analyses, in distilled or natural water. The quality assur­ Xi — individual values of analyses, ance support project prepares a natural-water X — average value of analyses, reference sample by collecting a sample of river and water, running a preliminary analysis for the ST = standard deviation. constituents of interest, spiking to higher levels If enough data are available and if the preci­ of concentration if necessary, and stabilizing the sion appears to vary with the concentration of solution. Stabilization is accomplished by filter­ the constituent, the precision is also expressed ing, stirring, and aerating quantities as large as in terms of a regression equation over a stated 300 gallons of the solution for 3 days, then ir­ range. If the precision does not appear to vary radiating it with ultraviolet radiation. The pre­ with concentration, it has been calculated by pared reference solution is then bottled and pooling the individual standard deviations over stored in sterile Teflon containers. Concentra­ the stated range, and the pooled standard devia­ tions of the constituents in the solution are not tion and its 95-percent confidence interval are quantitatively known, but the most probable stated. values are determined from the mean results of The stated precision of the analytical method determinations by several laboratories. Because needs to be considered when interpreting ana­ these solutions are ready for immediate use lytical data. For example, a concentration of 15 without further dilution, they are suitable for mg/L for total-recoverable iron and a concentra­ introduction to the laboratory as "blind" sam­ tion of 17 mg/L for dissolved iron cannot be con­ ples for quality control purposes. sidered to be significantly different if the Spiked or unspiked natural water or sediment precision of the analysis is ± 20 percent; of unknown concentrations, split in a central METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 11 location and supplied simultaneously to several 3. For general use, the proposed method should laboratories, is a further source of reference be at least equivalent to the current method material. This type of reference material is of with regard to precision, accuracy, limitation particular use in bottom-material analyses. of interferences, productivity, and the use of Similarly, although probably of more limited hazardous or toxic substances, and should usefulness, the duplicate samples submitted oc­ be an improvement over the current method casionally by field personnel can be evaluated in at least one of these areas. for precision information. Methods that do not meet all of the criteria The U.S. Geological Survey requires par­ may be conditionally accepted but are limited ticipation of its water laboratories in a desig­ to the application for which they were specifical­ nated quality control program. A part of this ly developed. Extension of the application re­ program requires frequent analysis of standard quires additional verification. reference water samples and of blind samples Clear records must be maintained on the prep­ of known composition. Complete records are aration of all standard solutions. All chemicals maintained of each laboratory's performance on must conform to the specifications of the Com­ these reference samples, and deficiencies are mittee on Analytical Reagents of the American promptly corrected. Chemical Society, and dilution water must be distilled or demineralized (passed through mixed-bed exchange resins). The latter process The Central Laboratories must be used if ammonia- free water is neces­ sary, and the water must be boiled immediate­ Use and documentation of standard laboratory ly before use for carbon dioxide-free water. procedures The periodic calibration and recalibration of each instrument must be recorded by the The acceptance of a new method or the modi­ analyst. Records must include the number of fication of an existing method for use in the U.S. standards used, the type and date of prepara­ Geological Survey Central Laboratories re­ tion of stock solution, if applicable, and the sam­ quires that several criteria be met: ple identification (such as a sample number). 1. A copy of the method in its final form and Noticeable blank drift or changes in readings of a research report must be presented. The standards must also be recorded and corrected. report must include all raw analytical data The monitoring of analyses by use of refer­ used in evaluating the method, an evaluation ence materials must be part of the operational of known and possible interferences, a single- routine. Within the U.S. Geological Survey Cen­ operator-precision statement for distilled tral Laboratories each section chief ensures that water and natural water solutions of the con* a sufficient number both of standards and of stituent being determined over the applic­ reference materials are incorporated in each set able concentration range of the method, and of analyses to give confidence in the results of an estimate of the method's productivity the set. Data are examined for indications of and personnel requirements. noticeable bias or inadequate precision; data are 2. The method must be tested in one or more filed in the section and are available for regular operating laboratories in parallel with the inspection. currently accepted method or methods for In addition, each section chief promptly re­ the same determination in order to develop ceives and evaluates information on all refer­ a set of data that covers the concentration ence samples submitted by the management. range of the method and the variety of The largest proportion of reference materials is natural water types that would be expected submitted daily by the laboratory management to occur nationwide. The evaluation of the directly to the laboratory as unknowns. Field results of this testing is the principal basis personnel submit to the laboratory, daily or for accepting a new or modified method and week depending on the frequency of an analysis, for establishing its precision. samples that are totally "blind." 12 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Analytical review procedures by this equivalence and that a chemical ionic balance does not ensure accuracy, even of these Control charts for each method must be kept major ions, because compensating errors can by the analyst and periodically reviewed by the exist in both cations and anions. section chief. The amount of scatter and the Depending on reference-sample results or on trends in values can then be easily spotted. Con­ other checks and after considering the precision trol charts on which reference samples near both of the method, the reviewer may decide to have the upper and lower range of the method are a water-quality sample reanalyzed. The reviewer plotted may be particularly useful. See chapter must take into account possible interferences A6 (Friedman and Erdmann, 1982) for more in­ in a method and should consider recommending formation on the preparation and use of control to the analyst that a different method be used. charts. The resulting concentration of the reanalysis In addition to evaluating control-chart and must be examined carefully, possibly with fur­ reference-material data, the Central Labora­ ther analyses made on the sample, before the tories quality-control staff reviews the com­ value is accepted. If an error has been made, an pleted analysis report for each sample prior to updated value is entered into the data file, and releasing the information. This review is aided a revised analytical report is generated. This by more than 100 computerized checks that are report receives another check by the labora­ made prior to printing the analysis report. The tory's quality control staff and is then released computerized checks include computation of the to the requestor. ionic balance and comparison to an allowable- error curve; comparison of dissolved solids to specific conductance and of the dissolved solids- References specific conductance ratio to predetermined ex­ pected ranges; a check on whether a total con­ Bates, R. G., 1964, Determination of pH—theory and prac­ tice: New York, John Wiley and Sons, 435 p. stituent concentration is equal to or greater Friedman, L. C., and Erdmann, D. E., 1982, "Quality than the corresponding dissolved concentration; Assurance Practices for the Chemical and Biological and a check on the constituents known to in­ Analyses of Water and Fluvial Sediment": Techniques terfere in current methodology above a certain of Water-Resources Investigations of the U.S. concentration level. Geological Survey, book 5, chapter A6, 181 p. Hem, J. D., 1961, Calculation and use of ion activity: U.S. The reviewer determines the validity of the Geological Survey Water-Supply Paper 1535-C. 17 p. individual error messages for each sample and ___1970, Study and interpretation of the chemical examines the analysis report for anomalies. The characteristics of natural water-revised edition: U.S. reviewer must be aware of the problems in Geological Survey Water-Supply Paper 1473, 363 p. achieving a balance when multivalent ions or Kolthoff, I. M., and Laitenen, H. A., 1941, pH and elec- trometric titrations: New York, John Wiley and Sons, partially dissociated substances are present and 190 p. must also be aware that the milliequivalents per Office of Water Planning and Standards, Monitoring and liter cannot be expected to balance if the con­ Data Support Division, and Environmental Monitoring centrations of all major ionic contributors are and Support Laboratory, 1976, Minimal requirements not determined. Likewise, the reviewer must for a water quality assurance program: U.S. En­ vironmental Protection Agency, EPA-440-9-75-010, U.S. realize that only predominant ions are checked Government Printing Office, 24 p. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 13 Laboratory Equipment and Techniques

Glassware and other containers platinum-tipped tongs to handle hot platinum vessels. Coarse crystal growth and embrittle­ All glass apparatus and containers used in ment may result from prolonged heating at high analytical work must be carefully selected to temperatures, heating under reducing condi­ meet the requirements of their particular use. tions, and heating phosphates or sulfates in the Although several types of special-purpose presence of organic compounds. Embrittlement glasses are available, borosilicate thermal- can be counteracted by rubbing the platinum- resistant types, such as Pyrex or Kimax, are ware with moistened sea sand. Gentle rubbing generally satisfactory for all ordinary labor­ with sea sand cold-works the metal and breaks atory purposes in water analysis. Borosilicate down the coarse crystal structure. Detailed in­ glass is especially suitable for storage of neutral structions for the care and use of platinumware or acid solutions, for volumetric glassware, and are distributed by manufacturers of these for conducting reactions. Because borosilicate vessels and are described in textbooks of quan­ glass is not entirely resistant to attack by titative analysis. strongly alkaline solutions, bottles of polyethyl­ ene or Teflon need to be used for storage of standard solutions of silica, boron, and alkali- Chemicals and solutions metals hydroxides. All volumetric glassware, such as burets, pipets, and volumetric flasks, must be of boro­ Purity silicate glass and must contain or deliver vol­ umes within the tolerances of the method. In Unless otherwise indicated, all chemicals addition if such glassware is frequently used to specified for use in analytical procedures shall measure strongly alkaline solutions, it needs to conform to the specifications of the Committee be recalibrated at frequent intervals. Directions for such calibration and testing of volumetric on Analytical Reagents of the American glassware are given by the National Bureau of Chemical Society. Those chemicals not listed by Standards (1959) and in standard texts of quan­ this organization may be tested as indicated by titative analysis. Rosin (1955). Chemicals used for primary stand­ Evaporations may be carried out in glass, por­ ards may be obtained from the National Bureau celain, zirconium, or platinum dishes. Platinum of Standards or from manufacturers marketing is preferred if the weight of the residue needs chemicals of comparable purity. Certified stand­ to be determined accurately, because the weight ard solutions may also be purchased. of platinum vessels is relatively constant. Water used to dilute samples or to prepare Although platinum is one of the most resist­ chemical solutions shall first be demineralized ant metals, it is not completely inert and is by passage through mixed cation-anion ex­ subject to embrittlement. The following precau­ change resins or by distillation. Its specific con­ tions are recommended: Never put solutions ductance at 25 °C must not exceed 1.0 ptS/cm, containing tin, mercury, or lead in a reducing and it shall be stored in resistant glass or environment in platinum; if the free metal polyethylene bottles. If more pure water is re­ should be formed it will alloy with the platinum, quired, this requirement is stated in the in­ especially if heated. Do not heat mixtures of dividual methods. hydrochloric acid with oxidizing substances, Carbon dioxide-free water may be prepared by such as nitrate or manganese dioxide; ferric boiling and cooling demineralized water imme­ chloride in hydrochloric acid attacks platinum diately before use. An equally effective means appreciably. Place hot platinum vessels on a of removing carbon dioxide is bubbling pure refractory material, never on a cold meted sur­ nitrogen in the water. Also, some ion-exchange face or on a dirty surface. Use only clean cartridges will remove dissolved carbon dioxide. 14 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS The pH of carbon-dioxide free water should be mL of reagent" requires the use of a volumetric between 6.2 and 7.2. pipet for the addition, but "add 5 mL" requires Ammonia-free water may be prepared by the use of a serological pipet; "dilute to 1,000 passing distilled water through a mixed-bed ion- mL" requires the use of a volumetric flask, but exchange resin. "dilute to 1 L" permits the use of a graduated cylinder. Test-sample volumes less than 5 mL should Standard solutions be avoided, if at all possible, because the calibra­ tion of 1- and 2-mL pipets is not as precise as The concentrations of standard solutions are that of the larger-volume pipets. Less error is indicated as the weight of a given element incurred if a suitable sample dilution is prepared equivalent to, or contained in, 1 mL of solution. and part of this dilution taken for the test sam­ The strengths of acids and bases are given in ple. Although the glassware is calibrated to terms of molarities or normalities. deliver a specific volume at 20 °C, the error in measurement incurred by pipetting samples at room temperature is insignificant for water Nonstandard solutions analysis. One gram of pure water is contained in 1.002 mL at 20 °C and in 1.007 mL at 38 °C; The concentrations of nonstandard solutions the maximum error in volume that will result are indicated in terms of the weight of solute from those temperature differences is only 0.5 dissolved in a solvent and diluted to a given percent. Brine samples should be brought as volume. Unless specifically indicated otherwise, near to 20 °C as possible before making dilutions the solvent is demineralized water of required for analysis. purity. Designation of concentration in terms The concentration of some inorganic consti­ of percent is not used. tuents in a water sample often will exceed the working ranges as recommended in the applica­ tion section of each method. For example, Accuracy of measurement sodium in brines will exceed the recommended range several fold. Dilution is normally used to Within the methods, significant figures are bring the concentration of any of these consti­ utilized to define the accuracy of weights and tuents into the appropriate range. This pro­ measures. Weighings will be accurate to the last cedure with proper technique is satisfactory for figure shown; for example, mass designated as dilutions of 1 to 1,000. The following techniques 4.532 g must be weighed accurately to ±0.0005 must be observed: A volumetric pipet (Class A) g, whereas a mass designated as 4.5 g must be smaller than 5.0 nnL must never be used and all weighed accurately to only ±0.05 g. volumetric flasks used must be Class A. Required accuracy for measurement of volume in the analysis and preparation of reagents is shown similarly. Standard solutions References are always prepared in and measured from volumetric glassware. The significant figures Rosin, Joseph, 1955, Reagent chemicals and standards: New York, D. Van Nostrand, 561 p. given for such measurements are in practical U.S. National Bureau of Standards, 1959, Testing of glass agreement with the tolerance limits for volu­ volumetric apparatus: U.S. National Bureau of Stand­ metric glassware used; for example, "Add 5.0 ards Circular 602. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 15 Analytical Techniques Gravimetry

Principles contained in a porcelain or platinum crucible or dish, or in a glass weighing bottle. Gravimetric determinations are based on the Increasingly, electronic analytical balances accurate measurement of the mass of a chemical are used. Because they immediately read the compound of known composition and purity. weight to 0.1 mg (or even to 0.01 mg), they are The trend in modern analytical laboratories is rapid and extremely accurate. Because most away from the long, tedious, time-consuming weights are determined by differences, elec­ gravimetric methods and toward faster instru­ tronic balances are easy to use and accurate for mental techniques, particularly techniques that determining solids as well as weighing of pri­ permit simultaneous determination of several mary standards. However, these balances re­ constituents. Nevertheless, some determina­ quire calibration more frequently than do tions can be performed only gravimetrically. non-electronic types. The following procedure is These include the determinations of the various recommended: forms of dissolved and suspended solids in a 1. Allow balance to warm at least 10 min. water sample. 2. Locate the calibration control on your balance and zero the balance. 3. Place weights on the pan to the total capaci­ Analytical balance ty of balance. If the balance does not read the same as the weight on the pan, turn the An analytical balance is an essential part of calibration control until it does. every gravimetric method. For many years, the 4. Remove the weights from pan and again zero balance commonly used for this purpose is the the balance. single-pan, direct-reading type, capable of meas­ 5. Repeat steps 1-4 until the balance gives the uring the mass of an object to within 0.1 mg. proper reading. Dual-range balances need to In order to maintain this sensitivity, great care be calibrated separately and will have sepa­ must be observed in the use and maintenance rate controls. of the balance. The balance must be located Balances are more and more being used in apart from the chemical laboratory, in a room conjunction with computers or their own micro­ free of laboratory fumes and strong drafts. The processors for routine determinations. In these balance must be placed on a vibration-free cases, weights are printed out and calculations stand, table, or shelf. Cleanliness is exceeding­ made so analytical data are transmitted direct­ ly important, and any material spilled in the ly to a data base with no manual data handling balance case must be cleaned up immediately. needed. Objects to be weighed must not be handled with the bare hands, but only with ivory-tipped forceps or platinum-tipped tongs. Accuracy Cleaning the balance thoroughly periodically and, at each time, checking its calibration is ad­ Gravimetric determinations can be among the visable. Weights conforming to Class S toler­ most accurate of all quantitative determina­ ances are satisfactory for routine water-analysis tions; they are time consuming, however. In applications. quantitative gravimetric measurements of the No chemicals are ever placed directly on the solids content of water samples, the uncertain­ balance pan for weighing. At the very least a ties about the composition of the material be­ tared weighing paper or aluminum pan is used. ing weighed usually exceed the uncertainty Most commonly the material to be weighed is involved in determining its mass. 16 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Titrimetry

Principles Standard solutions

Titrimetric analytical determinations are The standard solution used in titrimetry must based on the reaction of an accurately measur­ be simple to prepare and preferably stable for able volume of a solution of known concentra­ a comparatively long time to avoid the need for tion with an exact equivalent amount of the frequent restandardization. Quite commonly, substance being determined. The process of add­ the standard solution is not prepared directly, ing reagent solution to react with the sample is but is prepared at a concentration very close to known as titration, and the reactant added that desired and then standardized by titrating during the course of the titration is known as an accurately measured amount of a primary a standard solution. Titrimetric determinations standard. The primary standard must be of high are inherently simpler than gravimetric deter­ purity, or at least of accurately known purity, minations, and hence are usually preferred must be stable, and easily dried and weighed. where simplicity, ease, and speed of analysis An example of a good primary standard sub­ are important. Their sensitivity and accuracy stance is the sodium carbonate used to stand­ can approach those of careful gravimetric ardize the strong acid used in neutralization measurements. titrations. Many other primary standards are To be suitable as a basis for a titrimetric useful for various purposes; these standards are determination, the chemical reaction involved available, on specification, from chemical supply must proceed rapidly to completion with no side companies. The National Bureau of Standards reactions. The reaction between a strong acid supplies certified primary standard substances and a strong base is a good example of an ideal for the common titrimetric applications. reaction for a titrimetric determination. The titration of the anion of a weak acid with a strong acid does not involve an ideal reaction, Factor-weight computations but the reaction does proceed to an identifiable point of completion. Such a reaction is used to The concentration of the titrant may be ad­ determine the alkalinity of water samples, justed so that when a sample of given size is wherein the carbonate and bicarbonate anions taken for analysis, the volume of titrant in milli- are titrated with standard acid until poorly liters is in simple proportion to the concentra­ dissociated carbonic acid is formed. tion of the sought constituent, for example, in In addition to a straightforward chemical milligrams per liter. Some time is involved in reaction, an abrupt change of some property of initial adjustment of the titrant concentration, the solution must occur at the equivalence point but time is saved in the long run when many of the titration. This may be a change in hydro­ analyses are performed. Simplifying computa­ gen-ion concentration, a sharp increase in the tions in this manner also minimizes arithmetic concentration of one of the titrant ions, a error in handling the data. change in the electromotive potential, or even a change in the electrical conductivity of the solution. This abrupt change may sometimes be made apparent by adding to the system a color- Automated titrations change indicator solution that changes color abruptly when the reaction is complete at the Systems are available that automate the en­ equivalence point. When the equivalence point tire process of a titrimetric determination in­ is accompanied by a rapid change of pH, an in­ cluding the initial measurement of a sample dication of its occurrence may be monitored aliquot into a titration vessel. Titrations involv­ with a glass electrode. Such titrations are called ing colorimetric as well as electrometric detec­ electrometric titrations. tion of the equivalence point may be automated. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 17 The samples are placed in a revolving tray or equipment is particularly desirable when a great moving platform and are sequentially moved into many routine samples are to be analyzed. position for titration. As each titrant is com­ The trend in titrimetric titrations is also pleted, a printer records the sample number and toward microprocessors, which automatically the exact volume of titrant added. Such automat­ calculate and transmit the concentration of ic titrators speed the analytical process by free­ desired constituents. Understanding the chem­ ing the analyst for other duties while the titra- istry behind these reactions is increasingly tions are being carried out. They also have the important to properly program these sophis­ advantage of duplicating equivalence-point con­ ticated data-handling systems—now used in con­ ditions for all samples, avoiding individual judg­ junction with both colorimetric and electrometric ment on the part of the analyst. Such automated detection of equivalence point.

Atomic absorption spectrometry

Basic principles beam (measured in the absence of atomic vapor) and P is the radiant power of the beam after it When a beam of radiant energy is passed has passed through the atomic vapor. through a cloud of atomic vapor, certain very specific wavelengths characteristic of the ele- ment(s) in the vapor are absorbed. This princi­ Instrumental principles ple forms the basis of a very sensitive and highly selective method of analysis for most metallic Instrumentation for atomic absorption spec­ elements (Walsh, 1955). trometry consists of the following components, Each element absorbs energy at a series listed in the order of their function in the of wavelengths that constitutes the unique instrument: atomic spectrum of that element. Selectivity is (1) Source of radiant energy achieved by careful choice of the wavelength of (2) Sample chamber radiant energy passed through the sample (3) Wavelength selector Because atomic absorption occurs in extremely (4) Detector of radiant energy narrow (approximately 0.002 nm) intervals of the (5) Readout device (information processor) electromagnetic spectrum (Robinson, 1975), a A brief operational description of each compo­ wavelength can usually be selected that is ab­ nent follows. sorbed by only one constituent of a sample Under ideal conditions, the extent of absorp­ Radiant energy source tion at a specific wavelength is related to the con­ centration, c, of a given element in the vapor and The source of radiant energy must produce to the length, 6, of the path that the beam intense radiation at the exact wavelength absorb­ traverses through the vapor, according to Beer's ed by element to be determined. If Beer's law is Law: applied, the width of the emission lines in the spectrum of the source must to be narrower than A = a b c (1) the absorption lines of the element in the sam­ ple This is achieved by exciting radiation from In this equation, a is a constant of proportion­ low-pressure vapor of the element. TWo types of ality and A, the absorbance, is defined as: lamps are commonly used to produce atomic radiation: the hollow cathode lamp (HCL) and the A = log PJP (2) electrodeless discharge lamp (EDL). The HCL consists of a glass or quartz tube where P0 is the radiant power of the unabsorbed containing a small metallic cup that is lined with 18 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS (or made of) the element to be determined. This limit required, and the quantity of sample cup is given a negative electrical charge so that available. positively-charged ions of a low-pressure fill-gas, For flame atomic absorption, the sample is such as argon, are accelerated toward it, releas­ converted to an aerosol in a nebulizer and mixed ing metal atoms when they strike the cup. These with fuel and oxidant gases. This mixture is atoms are struck by other fill-gas ions, impart­ burned in a long, narrow burner that provides ing energy that raises them to excited atomic a long path-length for the radiant energy beam. states. Characteristic atomic spectra are emit­ Because the sample is greatly diluted by fuel ted by these excited atoms when they return to and oxidant gases, detection limits by flame the ground (normal) electronic state. atomic absorption are generally limited to In an EDL, a small amount of the element to 10-100 micrograms of metal per liter of solu­ be determined is sealed under vacuum in a small tion. Because the sample quickly passes quartz bulb, which is surrounded by a coil. through the flame and is lost, aspiration is con­ When a radio-frequency alternating current is tinuous during the analysis time. Therefore a passed through this coil, its energy is imparted relatively large volume (several milliliters) of to the metal vapor, causing it to emit the char­ sample is required. Operational ease and rela­ acteristic atomic spectrum of the metal. tively fewer interferences make flame atomic Either type of lamp is capable of producing absorption the fastest and simplest of the the spectrum of only one element (a few mixed- methods. element lamps are made that can produce spec­ In electrothermal atomic absorption, a few tra of 2 to 5 elements, but these are usually less microliters of sample are deposited into a small desirable due to lower intensity). HCL's tend to graphite tube at room temperature. The tube is be less intense than EDL's and have relatively then electrically heated through a pre-pro­ limited lifetimes, even if infrequently used. grammed cycle of four distinct steps: EDL's are generally preferred for those ele­ 1. Evaporation of solvent (approx 120°C) ments for which they are available. 2. Charring of volatile (organic) matter (several The radiant-energy beam from the source hundred degrees) lamp is usually modulated, either by "chop­ ping" the beam with a rotating mechanical 3. Atomization of the metal at high temper­ shutter or by modulating the power supplied to ature and determination (800-2500 °C) the lamp. This modulation enables the detector 4. Cleanout at very high temperature (3000 °C) to distinguish the source beam from unmodu­ This process has until recently been subject to lated radiation produced in the flame or furnace. so many interferences that the method of stand­ ard additions has almost universally been re­ quired. Recently, basic studies of the nature and Sample chamber origin of these interferences have lead to some revised techniques, that help to optimize the Atomic vapors may be produced by aspirat­ rate of vaporization and, thus, have reduced ing metal salt solutions into flames, by vaporiz­ interferences significantly. Among these new ing solutions in electrically-heated graphite techniques are vaporization of the sample on a tubes, or by chemically producing volatile metal small graphite platform (LVov platform) hydrides that are decomposed to atoms in mounted inside the furnace and addition of quartz tube-furnaces. Only one commonly deter­ chemical matrix modifiers. mined element, mercury, is volatile enough to Elements such as arsenic, selenium, anti­ produce measurable atomic vapor at room tem­ mony, and tin are usually converted to gaseous perature. These methods are designated metal hydrides, that are introduced into small "flame,'' ''electrothermal,'' ''hydride-genera­ quartz tube furnaces where the hydrides decom­ tion," and "cold-vapor" atomic absorption spec- pose to produce atomic vapor. Mercury is re­ trometry, respectively. The principal factors to duced to the elemental state and swept by a be considered in selecting among these methods stream of inert gas into a cool quartz tube in are the speed and ease of analysis, the detection the sample chamber. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 19 Wavelength selector absorbance, or (by comparison to standard solu­ tions of known concentration) into actual con­ After the radiant energy beam has passed centration readings. In older instruments, these through the sample, a monochromator is used readings were registered on chart recorders or to select only one of the characteristic lines of on panel meters. Modern instruments provide the element being determined. Monochromators digital readout, either on a display panel or on use diffraction gratings to spread the beam into a printer, and may be able to transmit readings a spectrum and from this spectrum an exit slit to computers. selects one wavelength for analysis. That wave­ Readings for flame atomic absorption are length may be in the visible (400-700 nm) or usually steady signals, which are averaged over ultraviolet (200-400 nm) region of the spectrum. a period of 0.5 to 5 seconds as appropriate to For most elements, a principal wavelength the noisiness of the signal. In contrast, elec­ and possibly one or more alternate wavelengths trothermal atomic absorption signals are trans­ are specified in approved methods. The selected ient, rising to a peak and decaying back to zero principal wavelength is very intense in the in only a few seconds. Such signals are meas­ source-lamp spectrum, strongly absorbed by the ured by either the height of the peak, or by inte­ atomic vapor, and free from interferences by grating the area under the peak. The choice will other elements commonly found in water sam­ depend on the relative precision and accuracy ples. Alternate wavelengths chosen for lower obtained by the two methods, which are gov­ sensitivity may be used for more concentrated erned by such factors as the sharpness of the samples, if specified in the approved method. peak and the shape, position, and intensity of Instrument performance is affected by slit the background absorption signal. width. A slit too narrow may degrade a detec­ tion limit because too little energy passes to the detector, and a slit too wide may result in noisy Analytical procedures signals or in erronous readings due to excessive background radiation or excessive curvature in Direct the calibration. The sample may be analyzed by direct intro­ duction into the flame or furnace, if the concen­ Detector tration of the element to be determined is great enough, and the interference effects are small The detector is usually a light-sensitive vac­ enough. Concentration is calculated by com­ uum tube called a photomultiplier. When a bias parison of the sample's absorbance to the ab- voltage of several hundred volts is applied to sorbances of a series of standard solutions. This a photomultiplier, it generates an electrical cur­ is performed either manually by constructing rent proportional to the power of radiant energy an analytical curve, or electronically by "curve incident upon it. These devices are very delicate fitting" in a microprocessor-controlled instru­ and should never be exposed to strong room ment. Although Beer's Law predicts a straight- lights, especially when the bias voltage is on. line relation between absorbance and concentra­ Such an exposure will produce "noisy" readings tion, some curvature is often found, and is for several days thereafter or may permanent­ tolerable up to a point. ly damage the detector.

Chelation-extraction Information processing It is possible to react many metal ions with Electronic circuitry, often including micro­ an organic chelating reagent, such as ammon­ processors, is employed to convert the PQ and ium pyrrolidine dithiocarbamate (APDC) or P values registered by the photomultiplier into 8-hydroxyquinoline and then extract the result­ human- or machine-readable indications of ing chelate into a water-immiscible solvent such 20 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS as methyl isobutyl ketone (MIBK), where the Ethanol) 95-percent: Denatured ethanol may be concentration of the metal to be determined is used. too low for direct measurement, or where seri­ Pyrrolidine, practical: CAUTION: Vapors are ous interferences are present. If, as is typically very toxic and liquid causes burns. Highly the case, 100 mL of a water sample is extracted flammable. with 10 mL of MIBK, the concentration of metal ions in MIBK is approximately 10-fold Procedure greater than in the original sample. In addition, detection limits are generally improved in 1. Dissolve 135 mL pyrrolidine, with con­ organic solvents, so the actual improvement in tinuous mixing, in 300 mL ethanol in a detection may be actually much greater than 1000-mL Erlenmeyer flask. 10-fold. 2. Attach the reflux condenser to the flask and Chelation-extraction can also be used to place in an ice bath. Cool for 30 min. Stir eliminate interfering substances which are not solution continuously, with a magnetic stir­ extracted under the conditions chosen. On the ring device. other hand, some substances in the sample may 3. Place 90 mL CS2 in a 250-mL separatory interfere with the chelation reaction by reacting funnel and slowly add the CS2 dropwise (2 preferentially with the chelating agent. to 3 drops per second) through the con­ APDC is used in several of the chelation- denser. Addition of the CS2 produces a extraction procedures in this chapter. Although strong warming effect; therefore, cool the it may be obtained commercially, a somewhat flask with ice at all times and stir con­ superior product may be prepared in the labor­ tinuously. After the CS2 has been added, atory. The preparation is simple, rapid, and re­ cool the mixture for an additional 15 min. quires little equipment. 4. Add 225 mL 8 TV NH4OH. APDC crystals will form rapidly. Chill the mixture for at CAUTION: The reagents and reactions are least 1 h. For maximum yield, place the flask potentially hazardous. Safety gloves and safe­ in a freezer for several hours. ty glasses must be worn, and a well-ventilated 5. Assemble a Buchner funnel, fitted with a hood must be used in all steps of the procedure. Whatman No. 41 paper, and vacuum- Reactions that occur release heat and must be filtering flask. Rinse the funnel with several performed in an ice bath with constant stirring. milliliters of chilled ethanol. 6. Dislodge the APDC crystals from the walls of the flask with a glass rod. Decant the solu­ Apparatus tion and APDC crystals into the funnel, and apply vacuum. Condenser, reflux, with ground glass joint 7. Rinse the flask with a small portion of chilled 24/40. ethanol and pour over the APDC in the fun­ Flask, Erlenmeyer, 1000-mL capacity with nel. Repeat this procedure until the filtrate ground glass joint 24/40. appears clear. Rinse the APDC twice more Funnel, Buchner, 16-cm diameter. with chilled ethanol. Funnel* separatory, 250 mL. 8. Dry the APDC by continuing the vacuum Magnetic stirrer. for about 1 h. 9. Remove the APDC from the funnel, place in Reagents an amber bottle, and store in a refrigerator. The yield is approx 180 g, about 75 percent Ammonium hydroxide, 8 N: In a well-ventilated of theoretical. hood, dilute 133 mL cone NH4OH (sp gr 0.90) to 250 mL with demineralized water and mix. Standard additions Carbon disulfide, reagent-grade: CAUTION: Vapor is very toxic and can be sorbed through The method of standard additions is a fre­ skin. Flammable. quently used analytical technique when certain METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 21 Interferences

Numerous types of effects can destroy the ideally simple relationship between absorbance and concentration. It is important that the analyst understand the basic nature and cause of each of these effects, so that potential sources of error can be anticipated and avoided.

2 4 Ionization effects In sample Added CONCENTRATION, IN MILLIGRAMS PER LITER A significant fraction of the atoms may be Figure 1.—Example of standard-addition method ionized if excessive heat is applied to a vapor­ ized sample. Because ions do not absorb at the types of interferences are present, or are sus­ same wavelength as neutral atoms, ionization pected because of unfamiliarity with the nature will cause a decrease in the intensity of the ab­ of the sample or the method of analysis. It is sorption signal. No systematic analytical error carried out by adding equal volumes of a blank will result, as long as this decrease occurs equal­ and three different known standard solutions ly in the calibration standards and in the sam­ of the metal to be determined to four aliquots ple. If, however, a particular sample contains a of the sample. The absorbance of each of these large amount of some easily-ionized element, an solutions is plotted on the vertical axis of a excess of electrons will be produced. These ex­ graph whose horizontal axis is concentration of cess electrons will repress the ionization equi­ metal added (to the right) and concentration of librium of the analyte metal, leading to an the unknown (to the left). An example is plot­ enhancement of the absorption signal in that ted in figure 1. The concentration of the un­ particular sample. A common example is the known solution is determined by extrapolating enhancement of the potassium signal in samples the line through the experimental points to the that contain high concentrations of sodium. horizontal axis. This is clearly too time- Elements on the left side of the periodic table consuming a procedure for high-volume routine (notably alkali and alkaline earth metals) tend analysis, because four measurements are re­ to be the most easily ionized, and are most sub­ quired to produce a single analysis. ject to ionization effects. Matrix effects, ionization interferences and Ionization interferences are controlled in one chemical interferences may be detected and/or of two ways; first, by keeping flame or furnace overcome by the method of standard additions, temperatures as low as possible when measur­ but two very important limitations must be ing easily-ionized elements, or secondly, by add­ noted carefully: ing a large excess of an easily-ionized substance (1) The method of standard additions is not (such as cesium) to both standards and the effective insurance against errors due to samples, so that the ionization equilibrium is en­ background absorption or spectral lines tirely driven toward the neutral atom in all interference; samples and standards. (2) A linear calibration curve throughout the entire concentration range utilized is ab­ solutely required. Chemical effects Methods for detecting and removing back­ ground effects and spectral line interferences Some metals tend to form thermally-stable are discussed in a later section. Nonlinearity can compounds when heated in flames or furnaces. be checked by analyzing the sample under These compounds prevent the formation of several successive dilutions from full concentra­ atoms in the sample chamber of the spectrom­ tion down to the detection limit of the method. eter, and thus lead to erroneously low absorbance 22 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

readings. The reduction of the absorbance of Table 4.—Temperatures of premixed flames calcium when phosphate or silica is present at Temperature high concentration is a classic example of a Oxidant Fuel (degrees Celsius) chemical interference because calcium phos­ Air Natural gas 1700-1900 phate and calcium silicate are dissociated only Air Hydrogen 2000-2050 at very high temperatures. A "releasing agent" Air Acetylene 2175-2400 (something that reacts with these anions more Nitrous oxide Acetylene 2600-2800 strongly than does calcium) will liberate calcium by tying up the interfering anions. Strontium and lanthanum are commonly used releasing such solutions by the atomizer. Again, this may agents for calcium and magnesium. Alternative­ usually be controlled by matching the density ly, a hotter flame may be able to thermally or viscosity of samples and standards, or by dissociate the stable compound. adding a noninterfering salt to the standards. Another example of chemical interference is Where matrix effects are severe or the matrix the formation of refractory (i.e., heat-stable) ox­ is completely unknown, the method of standard ides and carbides by certain heavy metals. In additions is highly recommended. this case, the use of hotter flames will at least partially dissociate these compounds. Table 4 shows the temperatures attained in commonly Spectral-line effects used analytical flames. The nitrous oxide- acetylene flame is frequently used to dissociate Spectral-line interference occurs when there thermally stable compounds such as calcium is overlap between the spectral line of the ele­ phosphate and refractory oxides. Oxide-forming ment sought and that of another element in the metals may benefit from the use of fuel-rich sample. Because wavelengths for analysis are flames, so as to decrease the availability of oxy­ selected to avoid overlapping lines, this problem gen atoms. Carbide-forming elements, on the seldom arises. However, when a nonanalyte ele­ other hand, may best be determined in non- ment is present at very high concentration, its hydrocarbon flames such as air-hydrogen, or in lines are broadened and may overlap the line of the presence of excess aluminum as a releasing the sought-for element. The analyst needs to be agent (Price, 1979). alert to the possibility of errors due to interfer­ ence of this type in samples of unusual or un­ known composition. One means of detecting Matrix effects spectral-line interference is to perform the deter­ mination at two different wavelengths. Spec­ Although both of the interferences previous­ tral-line interference is suspected when ly discussed might be called "matrix effects", determinations at two wavelengths yield dif­ this term is usually reserved for the simple ferent concentration values. physical effect of viscosity and surface tension on the efficiency of the nebulization process in flame atomic absorption. Typical of these ef­ Background absorption fects is the general decrease in absorbance signals which occurs with increasing acidity of Background absorption is a collective term the sample. Acid affects the viscosity and sur­ used to describe the combined effects of flame face tension of the sample, and therefore the absorption, molecular absorption, and "light rate at which the sample is nebulized into the scattering" by particles in the light path. Each flame. The best way to combat such inter­ of these effects results in a broad, flat absorp­ ferences is to calibrate using standards that tion band which is superimposed on the atomic have the same acidity as the samples to be line absorption, resulting in erroneously high analyzed. Unequal amounts of dissolved solids absorbance readings. Background absorption in samples and standards also may cause errors is particularly severe in the graphite furnace. in the analysis due to different nebulization of This effect is eliminated by use of a background METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 23 correction device which automatically subtracts Hydride generation may be automated using the "off-peak" absorbance, or background, from continuous-flow systems to add reagents in se­ the "on-peak" absorbance. quence and to provide the required heating and The most common type of background correc­ reaction-time delays. The volatile metal hydrides tor is the deuterium-arc (a continuum, or broad- so generated are separated from the sample solu­ spectrum source). Light from this continuum tion in a packed separator column, and are then source is passed through the flame or furnace swept into an electrically-heated quartz tube fur­ simultaneously with the hollow cathode or elec- nace by a stream of inert gas. The cold-vapor trodeless discharge lamp (sharp-line source). Be­ method for mercury may be similarly automated cause the lines in atomic spectra are so narrow, A significant recent advance in automation of the absorbance measured by the continuum atomic absorption is flow injection analysis (Bet- source is caused almost entirely by background, teridge, 1978; Wolf and Stewart, 1979). Under whereas the sharp-line source measures both microcomputer control, a few microliters of sam­ atomic and background absorption. The atomic ple are injected by means of a loop sampling absorption is computed by subtraction of the valve into a pumped stream of a carrier liquid background from the atomic-source absorbance, which flows continuously into the nebulizer of a A more recent development in background cor­ flame atomic absorption spectrometer. The rection is the Zeeman Effect background correc­ "plug" of sample disperses in the carrier stream, tor. When a body of atomic vapor is subjected producing a transient signal reminiscent of that to a strong magnetic field, a typical atomic ab­ observed in a graphite furnace analysis or sorption line is split into three components, one chromatography. The area under this peak is in­ at the original wavelength and one on either side tegrated and compared to standards for quantita- of it. These absorption lines are polarized, with tion. Principal advantages of this method are (1) the center one having opposite polarization from speed (as many as 400 determinations per hour) the two lines to the sides. Thus, under one con­ dition of polarization of the source beam, the and (2) increased precision due to the excellent atomic vapor does not absorb and only back­ control of the aspiration process afforded by ground absorption is measured at the center-line precision pumping of the sample stream. wavelength; whereas, under opposite polarization both the atomic vapor and the background ab­ References sorption are measured. Some loss of sensitivity is usually experienced, with a corresponding Beaty, R. D., 1978, Concepts, instrumentation and techniques in atomic absorption spectrophotometry: Norwalk, Conn., degradation of the detection limit. Also, some The Perkin-Elmer Corporation, 49 p. atomic lines give atypical splittings which do not Betteridge, D., 1978, Flow injection analysis: Analytical lead to useable results. However, in most cases Chemistry, v. 50, p, 832a-846a. Zeeman spectrometers are capable of handling Dean, J. A., and Raines, T. G, 1969, Flame emission and atomic extremely high backgrounds due to very "dirty" absorption spectrophotometry v. 1: New York, Marcel matrices. Although available for flame atomic ab­ Dekker, 435 p. Fernandez, F. J., Myers, S. A. and Slavin, W., 1980, Back­ sorption, the Zeeman Effect is primarily applied ground correction in atomic absorption utilizing the to electrothermal atomic absorption. Zeeman Effect: Analytical Chemistry, v. 52, p. 741-746. Kaiser, M. L., Koirtyohann, S. R., Hinderberger, E. J., and Automation techniques Taylor H. E., 1981, Reduction of matrix interferences in furnace atomic absorption with the Lvov platform: Spec- Autosamplers for both flame and electrother­ trochimica Acta, v. 36 B, PL 773-783. Price, W. J., 1979, Spectrochemical analysis by atomic absorp­ mal atomic absorption spectrometers are com­ tion: London, Heyden, p. 134. mercially available These devices are microproc­ Robinson, J. W., 1975, Atomic absorption spectroscopy, 2nd. essor controlled and, when used in conjunction ed: New York, Marcel Dekker, pi 20. with a printer, permit unattended operation for Walsh, A., 1955, The application of atomic absorption spec­ 40 to 60 samples. A few more advanced autosam- tra to chemical analysis: Spectrochimica Acta, v. 7, p. 108-17. plers have the capability to perform standard ad­ Wolf, W. R., and Stewart, K. K, 1979, Automated multiple ditions and (for furnaces) to introduce matrix flow injection analysis for flame atomic absorption spec- modifiers with each sampla trometry: Analytical Chemistry, v. 51, p, 1201-1205. 24 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Atomic emission spectrometry

Principles 1 i f hv2 Emission phenomenon 1 1 hv-j 1 When a metal atom in the gas phase ground tv state (M) is heated in an exitation source, energy ! ' f is supplied to the atom via collision with high- temperature atoms and molecules resulting in transitions of electrons within the metal atom £2 = hv-| to higher energy states. The excited atom M* E2 = can then lose energy by emission of a photon. The process can be represented thus: E-| = Figure 2.—Energy level diagram M + energy -* M* -»• M + hv

The energy of each of the emitted photons, hf, a suitable dispersion-detection system (spec­ equals the difference between the energies in the trometer or spectrograph); and (3) the resulting higher and lower energy levels (fig. 2). Each intensities must be compared with standards of transition emits a photon at a wavelength given known elemental composition. Solid samples are by X=c/^, and each element has a characteristic usually analyzed by arc or spark exitation pattern of emission wavelengths. In the simpli­ sources that atomize and excite elements direct­ fied example, (fig. 2) the population of atoms in ly from the sample. Solutions are generally the excitation source can be excited to either analyzed with flame or plasma exitation sources energy level one or two. Emission can occur by into which the sample is aspirated. In both transition from energy levels one or two to the cases, one or more elements can be quantified ground state, or by an intermediate transition simultaneously from the emission lines. from level two to one. Usually, one or more The fraction of sample atoms excited varies transitions ending in the ground state is the exponentially with the excitation-source most probable, resulting in one of the charac­ temperature—the Boltzmann distribution teristic emission wavelengths (lines) of greatest (Mavrodineanu and Boiteux, 1965) being a good intensity. approximation of the fraction if the source Emission from ions occurs in a similar way, attains or approaches thermodynamic equilib­ but because the energy levels are different from rium. Thus, the higher the temperature of the those of the atoms, the characteristic emission excitation source, the greater the emission in­ wavelengths are normally different as well. tensity for a given atomic concentration in the source. Moreover, the atomization (formation of atoms in the source) of many sample media is Quantitative analysis by emission more complete at higher temperatures: an in­ creasing concentration of atoms or ions in the In order for the emission phenomenon to be exitation source results from increasing temper­ used in quantitative chemical analyses, the atures. Although the analytical sensitivity following are necessary: (1) the sample must be might seem to increase and the detection limit atomized (constituents of interest converted to decrease almost without limit by increasing the atoms or ions in the gas phase) and the resulting temperature of the excitation sources at higher atoms or ions excited; (2) the resulting charac­ temperatures, several other phenomena occur teristic emission lines must be spectrally sepa­ that limit the benefit of higher source temper­ rated and their relative intensities measured by atures: ionization of the sample atoms, which METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 25 removes atoms from one emitting population to another, becomes increasingly important; the spectrum becomes more complex as more upper- level lines are excited; and, perhaps most im­ portantly, the source background emission also increases rapidly. The principal advantages of atomic emission are low analytical detection limits for many elements, simple instrumentation, good speci­ ficity and speed of analysis, and adaptation to simultaneous, multi-elemental analysis. The principal limitation is that atomization-excita- tion conditions can simultaneously be optimized to a degree satisfactory for quantitative analy­ sis for only a limited number of constituents. This limitation results about from the interde­ pendence of the atomization and excitation processes. Conditions to optimize one process may cause interferences in another. For exam­ ple, with relatively low-temperature sources, which minimize ionization and background, the population of excited atoms is low and the Figure 3.—Schematic of the nebulization, desolvation, analytical sensitivity and detection level are atomization, and excitation processes poor relative to those in higher temperature sources. With high-temperature sources, the population of excited atoms is large, but high flames range from the 2,000 to 3,000 K; this background and complex spectra are produced range results in good analytical sensitivity for that can adequately be resolved only by a high- elements that have relatively low excitation resolution spectrometric system. The other energies and that are atomized to an appreciable serious limitation is compound formation in the extent in the flame, that is, those having no atomization-exitation source, an effect that strong tendency toward compound formation. reduces the atomic population in the source and Flames are used most for analysis of liquid places an upper limit on sensitivity for many samples, either aqueous solutions or organic elements. solvents. Samples are introduced into the flame through a nebulizer, which converts the sample solution into a fine mist. Once in the flame, Types of excitation sources several processes occur in rapid succession: desolvation, atomization, and excitation, as il­ Flames lustrated in figure 3. Many nebulizer and burner designs have been developed. These are extens­ The chemical flame is the oldest emission ively reviewed by Mavrodineanu and Boiteux source, dating from the 1860's, and it is still in (1965). wide use today. Various types of chemical The production of gas-phase metal atoms flames and burner designs have been developed from the sample depends initially on the thermo­ for analytical work. As emission sources, flames dynamics and kinetics of the desolvation-atom- have much to offer. They are simple and inex­ ization processes. Commonly only a small pensive to operate, and the temperatures devel­ fraction of the sample reaches the flame Addi­ oped in the flames are adequate to excite 10 to tional atoms can be lost from the population of 20 metals, enabling analyses in water at the emitting atoms by compound formation with milligram-per-liter concentration range or less. flame gas products and by ionization, but ioni­ The temperatures of the most commonly used zation is a limiting factor for only a few elements 26 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS that are easily ionized in relatively hot flames. Direct-current arc By far the most important loss mechanism is compound formation of analyte atoms with The direct-current (d-c) arc discharge (Slavin, flame gas radicals. Many elements form stable 1971) is a widely used spectrochemical excita­ compounds in the flame, notably metal monox­ tion source and is almost always employed with ides. In the general equilibrium: a spectrograph or multichannel spectrometer. A high-current, low-voltage discharge is main­ M+O tained between two electrodes (usually graph­ ite), one containing the sample (usually the the forward reaction is exothermic, so an in­ anode) and operating in air (free-burning) or in crease in temperature shifts the equilibrium some other gas mixture at atmospheric pres­ toward the free metal atom if the oxygen con­ sure. Electrodes are most often made from high- centration remains the same. A decrease in the purity carbon, or graphite, because of their high- oxygen concentration also shifts the equilibrium temperature stability, ease of fabrication, and toward the free metal atom. Because one nor­ ease of purification. mally has little control over the temperature in With a high arc temperature, the analytical chemical flames, the more common approach to sensitivity is high, and low detection limits for shift the equilibrium is to lower the free-oxygen most elements result. Due primarily to wander­ content of the gases. One means of doing this, ing of the arc on the electrode surfaces during especially in hydrocarbon flames, is to make the the discharge, the reproducibility of the emis­ flame fuel rich. The slight drop in flame temper­ sion from sample to sample is poor. Conse­ ature under fuel-rich conditions does not reduce quently, reproducibilities in analyses are seldom better than about ±20 percent. This makes the the exitation efficiency substantially so a net d-c arc source better suited to qualitative or gain in free metal atom is achieved. Extracting semiquantitative analyses, rather than quan­ the constituents of interest from aqueous solu­ titative work. The tremendous sensitivity of tion into organic solvents reduces compound this high-temperature source combined with the formation by reducing source cooling from the capability for simultaneous multielement anal­ aqueous solvent and by improving the nebuliza- ysis make the d-c arc a very powerful and useful tion and desolvation efficiencies. analytical tool despite poor reproducibility. Flames also have some important limitations The d-c arc is used mostly for analysis of solid for use as emission sources: (1) temperatures samples, usually in powder form. Liquid sam­ much above 3,000 K cannot be obtained with ples can be analyzed by first evaporating the the usual fuel-oxidant combinations; for many sample to dryness in a cup electrode or by elements with high excitation energies this rotating a disc electrode into the liquid sample temperature is too low to excite a population of and then into the arc. atoms adequate for good analytical sensitivity; (2) the chemical environment of the flame fosters compound formation which effectively Alternating-current spark removes metal atoms of interest from the atomic emission process; and (3) considerable The alternating-current, or radiofrequency, background emission may be present in certain spark discharge is another widely used emission spectral regions (for example, the OH emission source (Slavin, 1971). It too is almost always between 300 and 350 nm and the C2, CN, and employed with a spectrograph or direct-reading, CH emissions from hydrocarbon-fueled flames). multichannel spectrometer. Although resulting Despite these limitations, flame atomic emis­ in poorer detection limits than the d-c arc, the sion remains one of the simplest and most sen­ alternating-current spark discharge provides a sitive analytical methods for easily excited higher degree of reproducibility and can be used elements that do not form highly stable com­ for quantitative analysis. pounds at high temperatures, such as alkali, The spark occurs repeatedly over a small area alkaline earth, and several transition elements. of the sample, and each spark is followed by an METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 27 "off" period. As a result of this alternating analysis caused by these effects, an excess of heating-cooling cycle, the bulk of the sample is an easily-ionized cation is usually added to the not heated to emission so that homogeneity and samples to buffer the ionization, and an internal limited-area studies can be made on solid sam­ standard is used for calibration. ples and solutions can be analyzed directly. Only a small fraction of the sample aerosol However, the small amount of sample con­ particles actually enters the plasma Because of sumed leads to poorer analytical sensitivity and this and the intense plasma background emis­ detection limits compared to other methods. sion, a high-resolution optical system is needed Conducting samples (for example, metals) are to achieve high analytical sensitivity. Reednick usually ground flat and used as one electrode (1979) has described a commercially available with a pointed graphite counterelectrode (point- d-c arc plasma jet used with a high-resolving- to-plane technique). Powdered samples (con­ power echelle spectrometer. ducting and nonconducting) are usually mixed with graphite powder and pressed into a pellet Inductively-coupled argon radiofrequency plasma torch that is used as the plane electrode. Solutions are usually analyzed using a porous-cup (graphite) In recent years, inductively coupled radio- electrode or a rotating-disc electrode. The for­ frequency plasma (ICP) torches have been ap­ mer consists of a porous-bottom graphite cup plied for spectrochemical analysis in both containing the sample solution and a counter- emission spectroscopy (Greenfield and others, electrode beneath the cup, discharging to the 1964; Wendt and Fassel, 1965) and absorption wet bottom of the porous cup. The rotating-disc spectroscopy. This type of torch was first de­ electrode consists of a rotating graphite disc, scribed by Reed (1961) as a new method of the lower edge of which dips into the sample generating a stable plasma at atmospheric solution and carries it to the spark-discharge pressure. region at the top of the disc. Numerous other The equipment for producing an inductively- electrode arrangements have been used, but coupled radiofrequency plasma torch consists these two are the most popular. of a quartz tube surrounded by a few turns of water-cooled tubular copper coil connected to an induction-heating power generator (fig. 4). One Direct-current argon plasma (plasma jet) end of the quartz tube is open and the other end receives the gas supply. The gas is heated by The d-c plasma jet developed by Margoshes the currents induced in the plasma. and Scribner (1959) is produced by forcing The coupling between field and plasma argon gas through an orifice housing a d-c arc improves as the plasma approaches the coil, discharge. Liquid samples are drawn into the causing the plasma to expand. The outer tube plasma by an apparatus described by Keirs and prevents the plasma from reaching the coil and Vickers (1977) in which liquid samples are causing a short circuit and, simultaneously, aspirated into a chamber, mixed with argon, thermally stabilizes the plasma. The heat from and swept through the orifice. the plasma is continuously removed by cool The temperature of the plasma approaches argon gas flowing between the outer and mid­ 10,000 K and, in addition to the usual nonion- dle tubes. A laminar stream of cold argon flow­ ized spectral lines, spectra of ionized atoms are ing through the space between the outer and the produced and in some situations predominate. middle tubes surrounds the plasma, stabilizes The actual temperature of the plasma depends the torch, and prevents wall contamination. The on the arc current, electrode geometry, and gas- inner nozzle permits the injection of an aerosol. flow rates. When gas flow is increased, electrical In general, inductively coupled plasmas have conductivity rises. This, in turn, results in a many properties in common with d-c argon higher current and, as a consequence, higher plasmas. The core temperature for the argon temperatures at the core of the discharge. plasma is about 10,000 K. The combination of Often, this effect varies as the composition of high-excitation temperature and inert atmo­ samples changes. To overcome problems in sphere provides a highly stable, sensitive, and 28 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS relatively interference-free excitation source for solution samples.

References

Greenfield, S., Jones, I. L., and Berry, C. T., 1964, High- pressure plasmas as spectroscopic emission sources: Analyst, v. 89, p. 713-20. Keirs, C. D., and Vickers, T. J., 1977, DC plasma arcs for elemental analysis: Applied Spectroscopy, v. 31, p. 273-83. Margoshes, Marvin, and Scribner, B. F., 1959, The plasma jet as a spectroscopic source: Spectrochimica Acta, v. 15, p. 138-45. Mavrodineanu, R., and Boiteux, HM 1965, Flame Spec­ troscopy: New York, John Wiley, 285 p. Reed, T. B., 1961, Induction-coupled plasma torch: Journal of Applied Physics, v. 32, p. 821. Reednick, J., 1979, A unique approach to atomic spectro- scopy-high energy plasma exitation and high resolution spectroscopy. American Laboratory, March, p. 32. Slavin, Walter, 1971, Emission Spectrochemical Analysis: New York, Wiley-Interscience, 254 p. Wendt, R. H., and Fassel, V. A., 1965, Induction coupled plasma emission sources: Analytical Chemistry, v. 37, p. 920-2.

Argon tangential coolant flow

/ Argon \

/ and \ < sample aerosol > \ F~ "I / \ Optional / >— argon \-J L flow J "Figure 4.—Plasma torch configuration

Colorimetry

Basic principles conversion of the constituent of interest into a substance whose solution or suspension is Colorimetric and spectrophotometric meth­ strongly colored and, thus, will absorb radiant ods in analytical chemistry are founded on the energy (Sandell, 1959; Skoog and West, 1982). METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 29 The basic principle dealing with the absorption and used for this purpose all contain five basic of all types of electromagnetic radiation is com­ components, not necessarily housed within a monly called Beer's law, but has also been called single unit. These are (1) a stable source of ra­ Lambert-Beer or Bouguer-Beer. Stated mathe­ diant energy, (2) a device that can be used to matically: control wavelength, (3) transparent containers for the sample and the solvent, (4) a detector A = -Iog10 T = log PJP = abc that measures radiant energy and converts it to some measurable signal, and (5) a readout where device (Skoog and West, 1980; Willard and others, 1981). A = absorbance, 1. Radiant energy source-usually a tungsten- T = transmittance (0-100 percent), filament incandescent lamp for the visible P0 — radiant power incident upon the sample, region; hydrogen or deuterium discharge P = radiant power leaving the sample, lamps for the ultraviolet region. a = absorptivity, 2. Wavelength control-a number of devices are b = light-path length in centimeters, and available including filters (absorption and in­ c = concentration of the absorbing species. terference) and monochromators utilizing either diffraction gratings or prisms. As this equation shows, the relation between ab­ 3. Sample and solvent containers-these must sorbance and concentration or pathlength is be manufactured from material that permits linear, and for a fixed concentration of an ab­ passage of the radiation of the wavelengths sorbing substance, the absorbance will vary of interest; commonly used materials include with path length. No exceptions have ever been quartz, fused silica, silicate glasses, and found to this relationship. On the other hand, plastic. Beer's law also states that absorbance and con­ 4. Detector-commonly some type of photoelec­ centration are directly proportional; many ex­ tric device that converts radiant energy into ceptions to this have been found, and these an electrical current, usually a photovoltaic must be considered in the evaluation of the utili­ cell, a phototube, a photoconductive cell, or ty of Beer's law in chemical analysis. Such ex­ a photomultiplier tube. ceptions are usually caused by either chemical 5. Readout-typically some kind of meter, a effects or instrumental limitations or both. digital readout, or a chart recorder. Chemical effects may result because Beer's law Detailed descriptions of the various components only holds for dilute solutions and instrumen­ can be found in several texts such as Skoog and tal limitations result from the use of light of in­ West (1980) and Willard and others (1981) or in sufficient monochromaticity or from a lack of manufacturers' brochures. proportionality between photocell (or equiva­ lent) response and light intensity. For more detailed discussions of Beer's law, the reader is Analytical procedures directed to any basic analytical chemistry text (e.g. Kolthoff and others, 1969; Skoog and West, Quantitative analysis by colorimetry is an 1980, 1982; Willard and others, 1981). extremely useful tool because it has wide applic­ ability, high sensitivity, moderate- to-high selectivity, good accuracy, and is easy and con­ Instrumental principles venient to use (Skoog and West, 1980). Addi­ tionally, many colorimetric procedures are Colorimetry (visible-light range) and spectro- readily automatable, which leads to significant photometry (ultraviolet- and visible-light range, increases in throughput rates. measuring absorption at a single wavelength) Before analysis is conducted, a set of work­ can be viewed as the instrumental measurement ing conditions and (or) instrumental settings of the absorption of radiant energy by a solution must be selected. The selection of a wavelength at a fixed wavelength. Instruments designed at which absorbance measurements are made is 30 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS of primary importance. The wavelength selected Interferences is commonly an absorbance peak, because changes in absorbance per unit of concentration Several factors influence the absorbance of a are at a maximum. In this way, maximum sensi­ material. These include the type of solvent, the tivity is obtained. This wavelength selection, in temperature, the solution pH, high electrolyte turn, provides several advantages in addition levels, and the presence of interfering sub­ to extending the determination to the lower con­ stances. The effects of these variables must be centration ranges: the interferences from other known and accounted for in establishing analyt­ ions are minimized, the effect of natural color ical conditions. Through proper selection and and (or) turbidity is reduced and may become maintenance of constant conditions, many of insignificant, small sample volumes can be used, these variables can be dealt with effectively so measurements are made less sensitive to prob­ that precise and accurate results are produced lems associated with a lack of monochromatic- simply by following the analytical procedure; ity, and Beer's law is adhered to in the analysis. however, some cases do require additional meas­ Once working conditions have been selected, ures to produce good analyses. Typically, addi­ analysis of samples can begin. In its simplest tional measures are needed because of the form, colorimetry or spectrophotometry entails presence of interfering substances that can have the duplication of a color formed by the constit­ either a positive effect (providing increased uent of interest by some type of reagent or color leading to higher absorbance readings and reagents. Thus, the color of some unknown sam­ hence, spuriously high results) or a negative ef­ ple solution becomes exactly the same as that fect (reducing the color causing lower absorb- of a solution containing a known concentration ances and, hence, spuriously low results). Interferences tend to be of two types, either of the constituent being measured when both physical or chemical. Physical effects encom­ solutions have the same amount of colored pass such things as natural color and turbidity, substance in a fixed volume (when Beer's law and almost always cause positive interferences. is followed). In actual practice, such a procedure Chemical effects can cause either positive or requires a great deal of time and effort and is negative interferences. An example of a positive generally impractical. Commonly, an analytical chemical interference is the presence of a sub­ curve for the constituent being determined is stance that reacts with a color reagent in the constructed by plotting absorbance versus con­ same way as does the constituent of interest. centration for known solutions. The standards Thus, the resulting color represents not only the used to construct such a curve are selected such constituent, but also the foreign substance. An that they approximate the concentration range example of a negative interference is the pres­ of the unknown samples that are being analyzed ence of a substance that inhibits the formation and generally cover a range in which Beer's law of color by complexing the constituent of inter­ is obeyed. The standards are treated in exactly est so that it cannot react with the color the same fashion as an unknown sample solu­ reagent. tion for the development of color and for the The simplest way of dealing with interfering measurement of absorbance. Plots of absorb­ substances is to dilute them to the point of ance versus concentration are made; then, by insignificance. This strategy works only if the measurement of the absorbance of an unknown sensitivity of the method is sufficient to deter­ solution, constituent concentration can be de­ mine the constituent of interest at low concen­ termined by reference to the existing analytical trations. Where dilution is not feasible, other curves. Such standard curves may be used re­ means must be used either to remove the in­ peatedly if identical analytical conditions are terfering substance, to increase the selectivity maintained; but, experience has shown that of the method, or to compensate for the effect these curves must be checked frequently be­ of the interfering substance. Removal may be cause identical conditions are rarely achieved accomplished in a number of possible ways. even over short periods of time (for example However, because the selection of an appro­ daily). priate procedure is dependent upon the sample METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 31 matrix and the constituent of interest, care their ability to analyze samples at a much faster must be exercised before adopting any pro­ rate than is possible using manual procedures. cedure. If turbidity is the problem, sample filtra­ Additionally, for many substances automated tion through a 0.45 ptm membrane filter may analyzers can produce results that are more eliminate it. Centrifugation is sometimes an­ precise and accurate than those of manual pro­ other satisfactory alternative. If color inter­ cedures. Finally, most automated analyzers feres, oxidation (using HNO3, or H2O2) or can be networked to mini-computers or main­ bleaching may possibly eliminate it. Chemical frame computers, which facilitates sample han­ interferences can sometimes be removed by dling, increases the speed and accuracy of data using ion-exchange resins, solvent extraction, transfers, and often provides real-time quality or precipitation. control. Today, automated analyzers for color- There are several ways to improve method imetry or spectrophotometry tend to fall into selectivity. Among such means are (1) adjusting one of three categories: continuous segmented the pH such that the constituent of interest flow, discrete, or flow injection. complexes with the color reagent much more Continuous segmented flow systems, such as favorably than with interfering ions or (2) using the Technicon Autoanalyzer, consist of a samp­ masking compounds such as EDTA that form ler, a proportioning pump, a cartridge (chem­ stable, unreactive complexes with interfering istry) manifold, a filter photometer, a recorder, ions and, thus prevent their reaction with the and a printer. Solutions are introduced into the color reagent. Compensation can be accom­ analytical system by the sampler. The sample plished in several ways. Direct compensation solutions are poured into small cups or test can be made by adding all reagents except the tubes that are placed in a rotating turntable, color reagent to the sample, placing the sample which advances at preset times, and the sam­ in the spectrophotometer, setting the absorb- ples are aspirated from each cup. A wash solu­ ance to zero, and then adding the color reagent tion is aspirated for a timed interval between and measuring the absorbance. This procedure samples. The proportioning pump works on a eliminates the natural absorbance of the water, peristaltic principle and meters samples, but it has limited utility (it can be used only reagents, and air bubbles into the flow system when the absorbance curve has a shallow slope through various sizes of flow-calibrated pump in the operating region). Another procedure en­ tubing. The cartridge manifold comprises the tails subtraction of natural color absorbance. To arrangement of reagent additions, mixing coils, do this, determine the absorbance of the test delay coils, and a heating bath (if needed to sample versus the blank sample specified for the make the reaction proceed at an acceptable method. Then determine the absorbance of the rate). These components vary in complexity and natural-color sample versus distilled water detail for each determination. The colorimeter under the same spectrometric conditions used is usually a two-photocell filter photometer. The for the test sample. The difference between the output from the colorimeter is measured on a two readings is the corrected absorbance and recorder and, possibly, on a printer. An analyt­ this value is used to obtain concentration. The ical curve can be constructed after a sufficient natural-color sample is prepared by adding all number of standards have been analyzed. Sam­ reagents but the indicator (color) reagent to the ple concentrations are then obtained from the same volume of sample water as used for the curve. Alternatively, a printer can be used, that test sample. Instead of the color reagent, add reads directly in concentration, but these values an equal volume of indicator solvent (usually must also be adjusted by reference to an distilled water). analytical curve. Flow injection analyzers are continuous flow Automated analyses systems that utilize an unsegmented analytical stream; thus, they differ from continuous seg­ The popularity of automated analyzers has mented flow systems because no air bubbles are increased greatly over the years because of involved. In construction, flow injection systems 32 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS are similar to segmented flow analyzers in that of tests (as many as 32), using the same instru­ they require a sampler, a pump, a reaction mentation. Requisite chemicals and diluents, for manifold, a detector, and readout device. The each test, are stored in the unit and dispensed differences involve the use of an injection valve as needed. These types of analyzers are and a microprocessor. The latter is necessary operated by programmable mini-computers that to control the timing of the system and to control sampling, reagent type and volume, reduce the data. A sample is introduced into the mixing, heating (if needed), incubation time, system as a plug (or slug) through the use of an wavelength selection, color measurement, calcu­ injection valve. This plug is then placed into a lation of analytical curves, and determination continuously flowing system that consists of a of sample concentrations. These concentrations carrier (usually distilled water, but reagents do not require additional correction because may also be included). Mixing of samples and they are automatically calculated from an ana­ reagents occurs through diffusion processes. As lytical curve. Data are provided in print and are a result, the reactions that produce color or tur­ also stored in the mini-computer for direct bidity rarely go to completion (do not achieve transfer to a mainframe system. Because dis­ a steady state). Therefore, three critical factors crete analyzers use open-reaction containers, must remain constant: (1) sample injection certain types of analytical procedures either volumes, (2) pumping rates for the carrier and cannot be employed or require that samples reagents, and (3) residence time in the analytical undergo some type of pretreatment prior to manifold and detector. insertion in the system. For example, the cad­ As samples are drawn into the system by an mium-reduction method for the determination automatic sampler, a pump simultaneously of nitrate plus nitrite cannot be adapted to a moves the carrier into the sample stream. A discrete analyzer. Likewise, the methylthymol sample fills the injection valve until it is loaded; blue method for the determination of sulfate, the valve is then opened and the analytical which calls for the removal of divalent cations stream is flushed out the valve, thus creating through the use of an ion-excange column, can­ the requisite plug. This stream then moves into not be run directly as with a continuous flow a reaction manifold where analytical processing system. However, if the samples undergo pre­ (addition of reagents, heating, dialysis, ion ex­ treatment to remove divalent cations, a discrete change, etc.) takes place. The resulting solution analyzer can be used to quantitate sulfate using is then passed through the flowthrough cell of this method. an appropriate detector, as in a segmented system. As with segmented flow, an analytical curve must be established so that sample con­ References centrations can be obtained. The absence of air segmentation leads to higher sample through­ Kolthoff, I. M., Sandell, E. M., Meehan, E. J., and Bruckens- put and there is little or no carryover between tein, S., 1969, Quantitative chemical analysis (4th ed.): samples. London, The Macmillan Co., 1199 p. Sandell, E. M., 1959, Colorimetric determination of traces Discrete analyzers, such as the American of metals (3rd ed.): London, Interscience Publishers Ltd., Monitor IQAS or the Coulter IKL, differ from 1032 p. both continuous segmented flow and flow injec­ Skoog, D. A., and West, D. M., 1980, Principles of in­ tion systems in that they operate exposed to the strumental analysis (2nd ed.): Sanders/New York, Holt, atmosphere, rather than seeded in tubing and Rinehart, and Winston Inc., 69 p. glass. Each reaction, which produces a colored Skoog, D. A., and West, D. M., 1982, Fundamentals of analytical chemistry (4th ed.): Saunders/New York, or turbid product, takes place in a discrete Holt, Rinehart, and Winston Inc., 603 p. (hence the name) container, which is usually Willard, H. HM Merritt, L. L. Jr., Dean, J. A., and Settle, disposable. In essence, these systems are "robot F., 1981, Instrumental methods of analysis (6th ed.}: chemists," capable of performing a large variety New York, D. Van Nostrand Co., 1030 p. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 33 Electrometry

Voltammetry The residual-current contribution to the total diffusion current can be evaluated by measur­ Voltammetry, polarography, is based on ing the current resulting from the supporting current-voltage measurements at an electrode. electrolyte alone. The residual current at any When a potential is applied across an electrode particular potential can then be subtracted from pair, the working electrode becomes polarized by the total current at that potential. assuming the applied potential. The working Polarography uses two basic forms for the electrode remains polarized, with no flow of cur­ working electrode—liquid or solid. The majori­ rent, until the potential difference between the ty of polarographic techniques use various con­ electrodes is sufficient to exceed the decomposi­ figurations of elemental mercury electrodes. tion potential of a particular electroactive Mercury electrodes generally take form either analyte in solution. At potentials greater than as a suspended mercury drop, known as the the decomposition potential, the electroactive hanging mercury drop (HMD) electrode or as a analyte is deposited on the working electrode dispersed thin-film electrode deposited on a con­ and the current begins to flow. As the applied ducting substrate, commonly referred to as the potential is increased further, the change in cur­ mercury thin-film (MTF) electrode. In general, rent levels, and becomes diffusion-limited. greater sensitivity may be obtained on MTF The potential at which the current produced electrodes, but HMD electrodes are simpler to by the electrochemical reaction reaches one half use and more versatile. Solid electrodes include its diffusion-controlled value is the half-wave platinum, gold, and various forms of graphite. potential, EJ/2. The half-wave potential is char­ Major limitations of solid working electrodes acteristic of the particular electroactive analyte are their variability in the activity of the de­ undergoing reaction and may be used for iden­ posited analyte and their inability to accommo­ tification purposes; however E1/2 is a function of date more than one simultaneously reduced solution conditions such as the supporting elec­ analyte. Both Imitations of solid electrodes pre­ trolyte, the pH, and the solvent system, to name vent useful current-potential response when ap­ a few. plied to stripping polarographic techniques. The current measured is the sum of the Modern polarographic instrumentation em­ Faradiac, capacitative, and residual contribu­ ploys a three-electrode system composed of a tions. Faradiac current is a result of electron working electrode, an auxiliary electrode, and transfer across the electrode-solution interface a reference electrode. The electrochemical reac­ as the result of the oxidation or reduction of the tion takes place at the working electrode, and electroactive analyte at the working electrode. the auxiliary electrode completes the circuit be­ Faradiac current is proportional to the concen­ tween the working electrode and the solution. tration of the analyte. The reference electrode serves as a contact to Capacitative current is the current needed to measure potentials applied to the working elec­ charge the double-layer capacitance at the sur­ trode. Platinum wires and foils are commonly face of the working electroda The separation of used as auxiliary electrodes. Reference elec­ charge at the solution-electrode interface acts trodes are usually either the familiar calomel much like a large capacitor with respect to the ex­ reference electrode or the silver-silver chloride ternal circuitry and requires current for charging. reference electrode. Capacitative current represents an inherent off­ A technique based on polarographic prin­ set or noise and can be the principal limitation ciples is anodic stripping voltammetry (ASV). to sensitivity of a polarographic measurement. ASV consists of two sequential steps. First However, capacitative current can be minimized the electroactive analytes are preconcentrated, by modulating the applied potential and by main­ or deposited, in the working electrode by reduc­ taining a constant working electrode area tion. After sufficiently long deposition times, 34 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS the concentration of the analyte will be greater E = Ex + 2.3 RUnF log A in the electrode than in the sample solution. Secondly each analyte is subsequently stripped, E is the total potential, in millivolts (mv), or oxidized, from the working electrode. In ASV developed between the selective ion and the the deposition step occurs at a sufficiently reference electrodes; Ex, in mv, varies with the negative potential as to deposit all the desired choice of reference electrode; 2.3 RTInF is the analyte species into the working electrode. Dur­ Nernst factor, where R is the gas constant, F is ing the stripping step the applied potential is the Faraday constant, n is the charge on the ion, stepped anodically under carefully controlled including the sign, T is the temperature in conditions, and the preconcentrated analytes degrees Kelvin; and A is the activity of the ion are subsequently stripped completely into the to which the electrode is responding. The term bulk solution. Carefully controlled conditions 2.3 RTTnF is equal (at T=25 °C) to 59.16 mv when are necessary to obtain precise current-potential n=l, 29.58 mv when n=2t etc responses for quantification and identification, As noted in the above equation, the electro­ respectively. chemical potential determined under real condi­ The total current generated by the electro­ tions is a measure of the activity of the ion in chemical reaction during ASV is, again, the sum question. This relates concentration to the in­ of the Faradiac, capacitative, and residual con­ teraction of the specific ion with all other ions in tributions. Differential pulse anodic stripping solution. The activity-concentration relationship voltammetry (DPASV) minimizes the capacita­ A can be described by the following equation: tive contribution by using a working electrode having a fixed electrode area and by superim­ A = cf posing a modulated pulse on the applied poten­ tial step. TVo current measurements are made where c is the concentration of the ion deter­ during each potential step. The first occurs just mined and / is the activity coefficient. The prior to the occurrence of the modulation pulse magnitude of the interaction depends on the and the second, immediately following it. The total ionic strength of the solution. This can be change in current between the pair of measure­ maintained at a constant level by the addition ments minimizes the capacitative current and of a high concentration of an inert electrolyte therefore enhances the signal-to-noise ratio. The to the system. Properly chosen, this addition contribution due to the residual current can be would not affect the equilibrium of the ion be­ eliminated by subtracting the reagent-blank ing measured and would stabilize the activity voltammogram from the sample voltam- coefficient. Therefore, to determine concentra­ mogram. tion, one needs only to provide the means for measuring with a readout device of some type this electrochemical potential with respect to a Ion-selective electrodes constant reference potential. By relating the potential measured by such a system to a series Ion-selective electrodes are electrochemical of known standard solutions, one can calibrate, sensors that relate concentration to electrical and, subsequently, determine the concentration potential. They operate in the same way, irre­ of the ion in an "unknown" sample. Additional spective of type, as does the classical glass elec­ information on the theory of ion-selective elec­ trode for the measurement of pH. Each sensor trodes and instrumentation may be found in the consists of an internal electrode and a mem­ manufacturers' literature; in Marenthal and brane that establish a potential. This potential Taylor, 1973; in Andelman, 1971; in Moody and is linearly dependent on the logarithm of the ac­ Thomas, 1971; and in Durst, 1969. tivity of a given ion in solution. Effective con­ For the purpose of discussion, ion-selective centration ranges usually cover several orders of electrodes can conveniently be grouped into magnitude. This electrode response is called three general types: solid state, liquid mem­ "Nernstian" and can be expressed mathematic­ brane, and gas sensing. Each one finds use in ally as follows: water-quality applications. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 35 Solid-state, ion-selective electrodes are nor­ but any mixing of phases must be minimal; mally constructed by sealing a crystal mem­ must not be too soluble in the sample solution, brane in an epoxy tube or other appropriate which will effect the limit of detection; must holder. Two types are available, either homogen­ have a viscosity high enough to prevent its eous or heterogeneous crystalline electrodes. rapid loss by flow across the membrane; must The homogeneous membrane electrode consists possess good stability; and must be available of an appropriate crystalline material prepared in a state of high purity with high-exchanger from either a single compound or from a homo­ capacity. The liquid ion exchangers are usually geneous mixture of compounds having satisfac­ high-molecular-weight organic compounds tory electrical resistance. The principal advant­ dissolved in an organic solvent. The organic ages of homogeneous electrodes are their low molecule has charged sites where the ion of in­ cost, fast response, long operative life, resist­ terest can bind to it. Both the exchanger and ance to corrosive acid and alkaline media, and the ion of interest move through the membrane. Nernstian behavior throughout many decades An internal filling solution and a silver wire of use. Electrodes of this type have been devel­ coated with silver chloride provide the electrical oped with high selectivity for bromide, chloride, contact. As with the solid-state electrode, a fluoride, iodide, silver, and sulfide. stable potential is developed and measured. A The fluoride ion-selective electrode consists of calcium selective-ion electrode as described by a single crystal of lanthanum fluoride (LaF3) Willard and others, 1974, is a good example. An membrane bonded into an epoxy body. A solu­ organic derivative of phosphoric acid is used as tion containing fluoride ions and a silver wire, the liquid ion exchanger that selectively forms which provides electrical contact to the back of a strong salt with calcium. Liquid-membrane the crystal, are sealed inside. The crystal is an electrodes selective for potassium, nitrate, and ionic conductor in which only fluoride ions are fluoroborate, to name a few, are also available. mobile. When the electrode is placed in an ex­ The most recent type of membrane intro­ ternal solution containing fluoride, fluoride ions duced, which is useful in water analysis, is the migrate across the membrane in an attempt to gas-sensing electrode. In addition to being used reach a state of equilibrium. A stable potential for measuring dissolved gases in solution, they is developed that is measured. can be used for measuring the ionic form of a The heterogeneous electrode consists of an ac­ constituent after appropriate sample treatment tive substance or a mixture of active substances to convert the ion to a gas. The sensor, com­ mixed with an inert matrix, such as silicone rub­ posed of an indicating and a reference electrode, ber or polyvinyl chloride, or placed on hydro- uses a gas-permeable membrane to separate the phobized graphite, to form a sensing membrane sample solution from a thin film of an inter­ that is heterogeneous in nature. An example of mediate solution, which is either held between this type of solid-state electrode is silver iodide the gas membrane and the ion-sensing mem­ embedded into silicone rubber to provide iodide brane of the electrode or is placed on the sur­ ion-selective response. face of the electrode using a wetting agent (for The second type of electrodes, liquid-mem­ example, in air-gap electrodes). This interme­ brane sensors, is similar to the solid-state elec­ diate solution interacts with the gaseous species trodes. Instead of a crystal-type membrane, in such a way as to produce a change in a meas­ these electrodes use a liquid ion exchanger tai­ ured value (e.g., pH) of the intermediate solu­ lored as a specific carrier for the ion of interest. tion. This change is then sensed by the The ion exchanger is held in place by a thin, por­ ion-selective electrode and is proportional to the ous, inert membrane. There is no shortage of partial pressure of the gaseous species in the prospective liquid cation- and anion-exchanger sample. An example is the ammonia-sensing materials for possible use in ion-selective elec­ electrode, which uses a hydrophobic gas-perme­ trodes; however, the successful fabrication of able membrane to separate the sample solution these electrodes presents problems, many of from the electrode-internal solution. Dissolved which are mechanical. The liquid ion exchanger ammonia in the sample diffuses through the must be in electrolytic contact with the sample, membrane in proportion to its concentration, 36 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS and, in turn, reacts in the internal solution to logarithmic scale. Millivolt scales are also pro­ produce hydroxide ions. This changes the pH vided for titrations and to verify proper elec­ of the internal solution. This change is meas­ trode operation. ured by a pH electrode located behind the mem­ An electrode interference is any species, other brane. Because the pH varies directly with the than the ion being measured, in a sample solu­ ammonia concentration, the electrode responds tion that can alter the potential measured by directly to ammonia. a sensing electrode. Two types of interferences Similar schemes can be devised for other exist: "electrode" and "method." Electrode in­ gases, including nitrogen oxides (NOX), carbon terferences are those substances that give a dioxide (CO2), hydrogen sulfide (H2S), and response similar to that of the ion being meas­ hydrogen cyanide (HCN). The ion-selective elec­ ured and whose presence generally results in an trode does not have to be a pH electrode as in apparent increase in activity or concentration the case for ammonia; the choice is dependent of the ion being determined—those substances upon the reaction of the gas in the interned that interact with the membrane so as to change solution. its chemical composition; and electrolytes pres­ A reference electrode is required to complete ent at a high concentration that produce ap­ the measuring circuit by providing a conductive preciable liquid-junction potentials. Method path from the sensing electrode, through the interferences are substances that interact with solution, to the readout device. The reference the ion being measured so as to decrease its ac­ electrode is the half of the electrode pair that tivity or apparent concentration, although the provides a constant potential regardless of solu­ electrode continues to report the true activity. tion composition. The potential developed by Generally, interferences for solid-state elec­ the sensing electrode is measured with respect trodes (except for fluoride) are species that form to this reference potential to give an overall more insoluble salts or metal sulfides than does system potential, which can be converted to the the ion of interest. Liquid-membrane electrodes level of the species sensed. Numerous types of react to the interfering ion as though it were the reference electrodes are available. The analyst ion of interest. Gas-sensing electrodes are af­ should consult the manufacturer's manual for fected by any species that has a finite vapor the reference electrode that should be used for pressure under the measuring conditions of the a specific selective-ion electrode. Differences in gas of interest. For a discussion of interferences performance among the various forms of for a particular species, see the individual con­ reference electrodes can be a major factor in op­ stituent of interest in this chapter. timizing a method of potentiometric analysis. Instrumentation required for potentiometric analysis with ion-selective electrodes is relative­ Specific conductance ly simple and inexpensive. Measurements can be made with conventional pH meters that pro­ Specific conductance is determined by using vide scale expansion. This type of instrument a Wheatstone bridge, in which a variable displays voltages, pH units, or other concentra­ resistance is adjusted so that it is equal to the tion units by means of a needle pointer and resistance of an unknown solution between two scale. Modern, direct-reading, solid-state poten­ electrodes either of platinized platinum or of tiometers are ideally suited for the requirements other suitable material such as graphite. The of water analysis. This type of meter provides null point is detected by an alternating current digital display in millivolt or pH units. Operator galvanometer, cathode-ray tube or digital read­ error is reduced with digital instruments, be­ out. Alternating current is necessary to prevent cause there is no need for interpolation and no polarization of the electrodes. Direct current risk of confusing scales. Instruments are produces gas bubbles on the electrodes that available under the designation of "Selective greatly increase the resistance and change the Ion-Meter/' which measure the potential of concentration of the electrolyte in the vicinity pH- and ion-selective electrodes and display it of the electrodes. The electrodes are coated with directly in concentration or activity units on a a thin layer of amorphous platinum, which METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 37 tends to absorb gases and catalyzes their re­ tions should be followed exactly for good union, thereby minimizing polarization. precision and accuracy. The electrode cell may be the dip, cup, or pipet type. The pipet cells are generally preferred for routine laboratory use: because they require a PH smaller volume of water for the determination, the water can be drawn directly from a narrow- pH meters measure the electrical potential mouth sample bottle without transferring it to between two electrodes immersed in the solu­ another container, the total time for the deter­ tion to be tested. The reference electrode main­ mination is less, and the water sample under­ tains a constant potential, and the indicating goes less mechanical agitation. Dip- or cup-type electrode maintains a potential dependent on cells are preferable for field work. the hydrogen-ion activity of the solution. The Temperature is an important factor in deter­ calomel electrode, which is a widely used ref­ mining the specific conductance of a solution. erence electrode in water analysis, consists of When the temperature of a solution increases, a mercury-calomel rod immersed in a saturated the conductance almost always increases. By solution of potassium chloride. This electrode convention, 25 °C is the standard reference has a half-cell potential of +0.246 volt. Elec­ temperature in most water-resources applica­ trical connection with the sample is provided tions. Thus, all specific-conductance determina­ through porous fibers sealed into the immersion tions are adjusted to and specified at 25 °C. The end. A hydrogen-ion-selective glass electrode is adjustment to 25 °C is achieved either auto­ normally used as an indicating electrode. The matically with a thermistor within the sensor glass electrode has several features that recom­ or manually at the conductivity bridge. Auto­ mend it for pH measurements. Among the most matic or manual temperature compensation is important are that it is not affected by oxidiz­ proportional to the inverse of the resistance of ing or reducing substances in the sample and a standard potassium chloride solution. that it can be used to measure the pH of turbid Many direct-reading conductivity bridges are samples or colloidal suspensions or both. The commercially available that are well suited for basic design is a silver-silver chloride or mer- both laboratory and field work. Manufacturers, cury-mercurous chloride electrode immersed in such as Beckman, Lab-line, YSI, etc., produce a solution of known pH and completely sealed lines of durable, lightweight equipment. These in glass. direct-reading conductivity instruments have The mechanism by which the glass membrane either a dial for manual temperature compen­ responds to hydrogen-ion activity involves ab­ sation or automatic temperature compensa­ sorption of hydrogen ions on both sides of the tion built into the conductivity cell and bridge membrane proportional to the activity of the circuit. As with all instruments, the manufac­ hydrogen ions in solution. The cell for measur­ turers' instructions and supplemental instruc- ing the pH of a solution is of the following type:

Ag°: AgCl Solution of Glass Solution of Hg°: HgCl. known pH; membrane; unknown pH

Glass electrode

The half-cell potential of the glass electrode is is used, because the resistance of the glass mem­ a logarithmic function of the difference in brane is so great. hydrogen-ion activity of the solutions on either Desired features in a line-operated pH meter side of the glass membrane. To measure this are a built-in voltage regulator; an accuracy potential a high-impedance electrometer circuit of at least 0.02 pH; stability of calibration; a 38 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS built-in temperature-compensating mechanism; References durable electrodes; and a design that permits Andelman, J. B., 1971, Analysis for metal pollutants: In­ insertion of the electrodes, a stirrer, and a buret strumental Analysis for Water Pollution Control, into a suitable vessel for titrations. For pH Michigan, Ann Arbor Science, p. 241-3. determinations in the field, the instrument Bates, R. G., 1978, Concept and determination of pH: In should also be rugged, compact, and battery Treatise on Analytical Chemistry, New York, Wiley- operated. pH meters should be carefully cali­ Interscience, part 1, v. 1, p. 821. Durst, R. A., ed., 1969, Ion-selective electrodes: National brated with two buffer solutions that bracket Bureau of Standards Special Publication 314, U.S. the pH range of the test samples, and the Government Printing Office, Washington, D.C., 452 p. calibration should be checked during extended Maienthal, E. J., and Taylor, J. K,, 1973, Electrochemical periods of operation. A third standard buffer techniques in water analysis: Water and Water Pollu­ should be used—the data of this third buffer will tion Handbook, New York, Marcel Dekker, Inc., v. 4, p. 1751-97. automatically indicate stressed or faulty elec­ Moody, G. J., and Thomas, J. D. R., 1971, Selective ion sen­ trodes if the theoretical versus actual curve is sitive electrodes: England, Merrow Publishing Co. Ltd., non-linear. 140 p.

Ion chromatography

Principles The second column, called the suppressor, de­ creases the background conductivity of the Ion chromatography (1C) has been used since mobile phase, called the eluent, to a minimal the early 1940's for separation of both organic level and pairs the ions in the sample to some and inorganic species. Analysis was relatively highly conductive species. Separated ions are easy when the ion being eluted from an ion- quantitated with a specific-conductance cell. exchange column had a directly measurable The basic procedure for anions, such as fluoride, property, such as absorption in the ultraviolet is shown in figure 5. A typical chromatogram or visible region of the spectrum, that could be for seven of the common anions found in water distinguished from the background. Specific- is shown in figure 6. conductance measurements were also used, but 1C is most useful for the determination of the high-background conductance of the electrolyte major ionic constituents of aqueous samples in (eluent) usually overwhelmed the conductance which no single ion is in great excess of the of eluting ions. Small and others (1975) solved other ions. The ions are determined sequential­ this detection problem by adding a suppressor ly using only a small aliquot of sample, and column downstream from the separator column detection limits for many of the ions are lower that suppressed or neutralized ions of the back­ when 1C is used instead of other techniques. ground electrolyte. Recent advances in cells and Chromatographic separation of the ions elimi­ electronic suppression have revived the original nates many of the interferences associated with technique. However, methodology in this man­ other techniques, permits the use of universal ual uses the technique of Small and others detectors, and is capable of determining dif­ (1975), and discussion is limited to the two- ferent species of the same ion in some cases. column technique. A sample is injected into a liquid mobile phase being pumped through two ion-exchange col­ Apparatus umns placed in series. In the first column, called the separator, ions are separated on the basis The 1C technique and equipment are rapidly of their affinity for exchange sites on the resin. changing and improving. Better pumps, sample METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 39

Ion chromatography - anions

Effluent reservoir CO3~or HC<>3 = X"

Pump

Injection port

-**R F"+X~ Separator R* X" Inject column R*X"*NaF"

Figure 6.—A typical chromatogram for seven anions Suppressor Na**HF column R" H* -»*R" Na++HX Determining low concentrations of ions in precipitation samples requires that the conduc­ Conductivity tivity meter on the ion chromatograph be set detector to more sensitive scales. Hence the "water and carbonate dip" interference with fluoride and chloride determinations at low concentrations Waste Recorder is more pronounced. To eliminate the "water and carbonate dip/' a stronger eluent is added Figure 5.—Ion chromatography system for anions to each sample to increase the conductivity to the same level as that of the eluent that flows injection systems, separator resins, suppression through the system. This modification of the ion techniques, and a proliferation of detectors chromatograph can be made by installing two promise greater accuracy, precision, and pulseless pumps, which permit the automatic versatility. addition of stronger eluent to each sample. The ion chromatographic schematic in figure 7 in­ cludes this automatic addition. Pumps

Liquid chromatography requires a highly Sample-injection systems reproducible eluent flow rate for reproducible results. For this reason, intermittent-displace­ Reproducible sample injection can be very dif­ ment-type pumps are used in 1C instruments. ficult to achieve in 1C. One problem is that the Recent advances in pump technology have ions amenable to determination are ubiquitous resulted in a new generation of intermittent- in the laboratory environment, presenting displacement-type pumps for 1C use. They have substantial opportunities for sample contamina­ pump heads made entirely of nonmetallic parts tion. Especially problematic is the determina­ and can operate at pressures as high as 2,000 tion of ions at low levels in samples such as pounds per square inch. These pumps also in­ precipitation or boiler feed water. corporate a precision pressure transducer in The most common sample-injection technique dual-pressure and flow-rate feedback loops to for 1C is to manually rinse and fill a sample loop provide a constant-pressure, essentially pulse­ from a plastic syringe, and then place the loop less, eluent flow. into the chromatographic system, causing the 40 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS ions and results in good mass-transfer charac­ teristics for the resin. The stability of these resins throughout the entire pH range is their most important feature. S-DVB packings do not undergo degradation •T" Connector even under drastic conditions. Swelling in organic solvents is minimal. Ion selectivities on Cone:*ntraU4 I I- •lu«nt•nt pump i——j——* these resins are similar to those for conventional S-DVB packings. They are resistant to over­ loading and poisoning. Depending on the analyte, two types of S-DVB-separator packings are used. Cation sep­ arators use surface-sulfonated S-DVB resin and have typical capacities in the range of 0.005 to R*g«n*ratlon solution out 0.1 me/g. Anion-separator resins have an inert, hydrophobic, S-DVB-polymer core. Surround­ ing this core is a layer of solvated sulfonic acid Fiber •uppr«*«or*> groups similar to that used in cation separators. This layer is coated with a uniform monolayer • Regeneration solution of laminated latex. The latex is attached to the In sulfonated surface by a combination of elec­ ---*• Integrator trostatic and Van der Waals forces. The capaci­ ty of these anion-exchange resins is similar to Figure 7.—Ion chromatographic schematic diagram the capacity of the cation exchangers. Pellicular silica-based packings, which have functional ion-exchange groups attached by the sample to be swept onto the separator column usual silane reactions, are of some use in 1C, as by the eluent flow. well as resins such as silica-coated polyamide Automated instruments may use a pump to crown resins (Igawa and others, 1981), dynamic­ fill the sample loop. This pump should always ally coated reverse phases (Cassidy and Elchuk, be on the waste side of the sample loop to pre­ 1982), and specially treated polymeric adsorb­ vent contamination from the pump mechanism. ents of high-surface pourous polymers (Gjerde Another approach is to use an automatically ac­ and Fritz, 1981). These techniques are in their tuated valve to open a vacuum line and draw infancy, having the pH limitations of silica, the the sample through the sample loop. In any liability of the silyl-carbon bond, or mechanical case, some means must be incorporated in the instability under the conditions necessary for injection- system design to divert eluent flow good ion separations. while the sample loop is being filled or moved in and out of the chromatographic system. Otherwise, a pressure spike will upset the Suppressor resins system upon sample injection. The original suppressors, still widely used, are columns packed with Dowex 1X8, 200-400 mesh Separator resins in the hydroxide form for cation analysis and Dowex 50W X8, 200-400 mesh in the hydro­ The most commonly used separator resins are gen form for anion analysis. These columns con­ S-DVB (styrenedivinylbenzene) based. These vert eluent ions to a low-conductivity species and are pellicular resins, which have exchange sites paired analyte ions to highly conductive hydro- only at or very near the surface of the S-DVB nium or hydroxide ions. These two processes, col­ support. This leads to high efficiency by mini­ lectively called suppression, enable for very mizing the diffusional pathways of the sample sensitive conductivity detection of ionic analytes. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 41 This type of suppression system has two ma­ fiber is a cation exchanger containing sulfonate jor drawbacks. The suppressor resin is slowly (R-SOjj1) exchange sites. When an eluent is exchanged during a series of analyses and must flowing through the fiber, the cationic Na+1 be regenerated to the hydrogen or hydroxide ions are attracted to the SO^1 groups in the form periodically. Regenerating the suppressor membrane wall, as are the protons present in resin is time consuming and requires an entire the regenerant solution. The fiber-suppressor IC-instrument subsystem consisting of a regen- reactions are as follows: erant reservoir, a regenerant liquid pump, valv- Inside a tubular cation-exchange membrane: ing, and plumbing. The other major drawback is the increase in system volume that results 2 Na+1 + CO§2 + 2(resin H+ 1) -* H2CO3 from the suppressor column. Although having +2(resin as large a suppressor as possible is desirable to avoid frequent regeneration, the larger the sup­ Na+1 + HCOg1 * resin H+ 1 -* pressor bed, the greater the peak broadening resin Na+1 +H2CO3 and general loss of chromatographic resolution. Recently, Stevens and others (1981) intro­ Resin H+ 1 + NaF -> resin Na+1 + H+ip-1 duced a hollow-fiber ion-exchange suppressor as shown in figure 8. It shows the reactions that Outside a tubular cation-exchange membrane: occur across the membrane wall. Sodium bicar­ bonate/sodium carbonate eluent flows through H2SO4 -*2H+1 + SO}2 the interior of the fiber and sulfuric acid regen­ eration solution flows countercurrently. The 2Na+1 + SC>42 -* Na2S04 (to waste)

- — Plane Regeneration solution Na2 SO4 out ^— Eluent Eiuent Na2 CO3 or —»»< H2CO3 out Na HCO3 in Regeneration solution H2SO4 in

Side view of fiber suppressor

Plane

._ Cation exchange membrane

Top view of fiber suppressor

Figure 8.—Fiber suppressor 42 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS This device enables the near steady-state ex­ One problem with using conductivity for change of ions across the wall of a sulfonated detection is its dependence on temperature. For polyethylene hollow fiber, resulting in the sup­ each 1 °C change in temperature, there is a cor­ pression of eluent and analyte ions. responding change of about 2 percent in the The hollow-fiber suppressor eliminates the equivalent conductance. This temperature need for periodic suppressor regeneration, but dependence severely limits analytical reproduci- results in greater band spreading and subse­ bility if precautions are not taken to ensure quent loss of resolution than is obtained using temperature stability during 1C analyses. a small bed-volume, resin-filled suppressor col­ Instruments, which are presently produced, umn. Stevens and others (1982) reported that incorporate a microprocessor-controlled conduc­ band spreading is reduced and resolution im­ tivity detector that allows precise, accurate proved when the hollow fiber is surrounded with compensation for environmental-temperature inert beads. Although some problems still need fluctuations. This imparts both long- and short- resolution, the steady-state suppressor device term baseline stability and improved signal-to- should improve greatly the utility of 1C for ac­ noise ratios. curate and precise quantitation. Upon entering Conductivity is not the only means of detec­ a fiber suppressor, the eluting base, for exam­ tion compatable with 1C. Electrochemical detec­ ple, NaOH, is removed by the acid resin: tors are also commercially available. This type of detector works best in a high-conductivity Resin H+1 + background environment so no eluent suppres­ resin Na+1 +H2O sion is required. The detector consists of a flow cell with three electrodes: a silver-silver chloride and the analyte anions (A~) are converted to reference electrode, a platinum or steel counter their acids: electrode, and a silver or platinum working electrode. Resin The silver working electrode can be used to determine species such as cyanide, sulfide, and bromide. Setting the operating potential proper­ which pass through the fiber suppressor and in­ ly enables the detection of small amounts of to a flow-through conductivity cell where they bromide, for instance, in the presence of chloride are detected. concentrations high enough to swamp the bro­ mide signal from a conductivity detector (Pyen Detectors and Erdmann, 1983). Unfortunately, reactions at the silver working electrode involve the cata­ Small and others (1975) stated that it would lytic oxidation of the silver electrode itself. For be desirable to employ some form of conducti- this reason variations in detector response metric detection as a means of monitoring ionic within relatively short periods of time must be species in a column effluent, because conductiv­ expected and frequent cleaning of the electrode ity is a universal property of ionic species in surface is required. Suppression is unncecessary solution and because conductance shows a sim­ and toxic analytes, such as cyanide, remain in ple dependence on species concentration. How­ basic solution throughout the analysis (Bond ever, with older types of conductivity detectors and others, 1982). the species of interest was generally "swamped Recently, post-column-reaction technology has out" by the more abundant eluting electrolyte. been developed to produce complexes with the With the addition of the suppressor column, analyte ions that absorb in the near ultraviolet this problem was solved as discussed pre­ and visible portions of the spectrum. Detection viously. Again, note that modern conductivity is achieved using a photometer equipped with detectors have been refined to electronically a flow-through cell. Some transition metals and suppress the eluting electrolyte. This will not different species of the same metal ion have been be discussed further since the methods in this determined by this technique. One of the in­ chapter utilize chemical suppression. teresting applications involves the use of eluents METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 43 such as tartaric acid. This weakly acidic eluent References permits the use of high-efficiency, silica-based separator resins. The resulting metal-tartrate Bond, A. M., Heritage, I. D., and Wallace, G. G., 1982, Simultaneous determination of free sulfide and cyanide complexes are monitored photometrically as by ion chromatography with electrochemical detection: they elute off the separator column. Analytical Chemistry, v. 54, PL 582-5. An endless variety of detector types and con­ Cassidy, R M., and Elchuk, £, 1982, Dynamically coated col­ figurations seem to be available. This instru­ umns for the separation of metal ions and anions by ion mentation is perhaps where real progress in 1C chromatography: Analytical Chemistry, v. 54, pi 1558-63. Gjerde, D. T., and Fritz, J. &, 1981, Sodium and potassium methodology will come in the near future. benzoate and benzoic acid as eluents for ion chromatog­ raphy: Analytical Chemistry, v. 53, p. 2324-7. Hedley, A. G., and Fishman, M. J., 1981, Automation of an Automation ion chromatograph for precipitation analysis with com­ puterized data reduction: U.& Geological Survey Water- Resources Investigations 81-78, 33 p. Either peak height or peak area can be used Igawa, M., Saito, K., Tfcukamoto, J., and Thnaka, M., 1981, Ion to quantitate 1C analyses with conductimetric chromatographic separation of anions on silica-coated polyamide crown resin: Analytical Chemistry, v. 53, p. detection. Measuring the peak heights or peak 1942-4. areas of both samples and standards can be Fyen, G. SL, and Erdmann, D. E., 1983, Automated determina­ tedious and time consuming because large tion of bromide in waters by ion chromatography with amounts of data are generated in analyzing a an amperometrie detector: Analytica Chimica Ada, v. 149, sample. The use of an electronic integrator p. 355-8. Slanina, J., Lingarak, W A., Ordelman, J. E., Borst, P., and capable of reporting and storing both peak Bakker, F. P., 1979, Automation of the ion chromatograph heights and areas facilitates the process. Hedley and adaption for rainwater analysis: Ann Arbor, and Fishman (1981) described an automated Michigan, Ann Arbor Science, Ion Chromatographic system that was used for the determination of Analysis of Environmental Pollutants, v. 2, p. 305-17. Small, H., Stevens, T. SL, and Bauman, W. C, 1975, Novel ion six anions in precipitation samples. The ion exchange chromatographic method using conductimetric chromatograph was interconnected to an auto- detection: Analytical Chemistry, v. 47, p. 1801-9. sampler and a computing integrator. Slaina and Stevens, T. S., Davis, J. G, and Small, H., 1981, Hollow fiber others (1979) also described a data-acquisition ion-exchange suppressor for ion chromatography: Analytical Chemistry, v. 53, p. 1488-92. and reduction system using a minicomputer. Stevens, T. &, Jewett, G. L., and Bredeweg, R. A., 1982, P&cked Presently, commercially automated instrumen­ hollow fiber suppressor for ion chromatography: tation is available. Analytical Chemistry, v. 54, p. 1206-8.

Sample Preparation and Pretreatment

Tb determine the total concentrations of metals 2. Summary of method (dissolved plus suspended forms), the unfiltered 2.1 The sample is sieved, using a 2-mm sample (water-suspended sediment mixture) plastic sieve, and the material passing through must be completely digested with a strong min­ this sieve saved for analysis. A portion of the eral acid or mixture of acids to bring the metals sample is then air-dried. into solution. Digestion is also necessary for 2.2 The percent moisture remaining in the analyses of samples of bottom material In addi­ air-dried sample is determined by heating at tion, the organic matter, which is nearly always 105 °C. This permits computation of all constit­ present, must be removed by oxidation and vola- uents determined to an oven-dried basis if tization. On samples of bottom material, analyt­ desired. ical data are reported on a dry-weight basis. How­ ever, if there is a possibility of volatilizing any 3. Interferences of the constituents during air or oven drying, the Nona analysis must be made on a weighed portion of the as-received (wet) sample The percent of mois­ 4. Apparatus ture is then determined on a separate portion. 4.1 Desiccator, charged with "Drierite" or its The concentration values obtained on the wet equivalent. sample are then converted and reported on a dry- 4.2 Drying ovent 105 °C, uniform temper­ weight basis. ature throughout. The proper subsampling of bulk samples of bot­ 4.3 Sieve, plastic, with 2.00-mm openings. tom material presents unique problems. For most 4.4 Tray, drying, white-enameled, size 34 cm samples, splitting the sample using a Jones-type (13-1/2 in.) by 24.5 cm (9-5/8 in.) by 2 cm (3/4 splitter is satisfactory. Alternatively, subsamples may be conveniently extracted with a small- in.) or equivalent, diameter coring device, commonly glass tubing, 4.5 Weighing bottle, cylindrical, 12-mL to minimize the risk of metal contamination of the capacity. sample. Ordinarily, bottom-material samples are sieved before analysis, and only the portion pass­ 5. Reagents ing through a 2-mm screen is taken for analysis. None required. The use of an all-plastic screen eliminates the risk of introducing metals into the sample 6. Procedure 6.1 Transfer the entire sample to a plastic sieve having 2.00-mm openings. Shake and tip Sample preparation, the sieve firmly but gently, washing with mini­ bottom-material mal amount of demineraUzed water necessary to sieve all material less than 2-mm diameter. (P-0520-85) Discard material retained on the sieve. 6.2 Air-dry the sample. Spread a represent­ 1. Application ative portion of the sample in a thin layer on a This method may be used to air-dry samples flat enamelware tray or glass watchglass, and of bottom material for subsequent analysis. allow it to stand exposed for 24 h, or until dry. 45 46 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS The drying must be conducted in a place free through the sieve is subsampled by coring. of potential contamination. 2.2 The percent moisture is determined by 6.3 Portions of the resulting air-dried and drying a suitable portion of the sieved wet sam­ well-mixed sample are taken for subsequent ple (method P-0590) in order to compute all analyses. constituents determined on an oven-dried basis 6.4 Determine the percent moisture on a por­ (105 °C). tion of sieved and air-dried sample. Weigh be­ 2.3 Care must be taken that the sieved sam­ tween 1 and 2 g, to nearest 0.1 mg, into a tared ple is well-mixed and that the percent moisture weighing bottle. Place the weighing bottle con­ determined on the separate subsample reflects taining the accurately weighed sample in a dry­ the moisture content of the subsample ing oven and heat for 2 h at 105°C. Cool in a analyzed. desiccator for 30 mm and immediately weigh. 2.4 In general, when peat-like material com­ poses the majority of a sample, it should be con­ 7* Calculations sidered as part of the sample even though it will 7.1 Compute the loss in weight of the sam­ not pass easily through a 2-mm sieve. (Such ple, in grams, on heating at 105 °C. samples are not to be confused with samples 7.2 Compute the percent moisture of the consisting almost solely of leaves and twigs.) sieved and air-dried sample as follows: 3. Interferences None. Percent„ x moisture— ———:————r~rloss in weight (g) X100 sample weight (g) 4. Apparatus 4.1 Glass tubes, both 10-mm ID and 20-mm 8. Report ID have been found satisfactory. Report percentage of moisture to two signif­ 4.2 Sieve, plastic, with 2-mm openings. icant figures. 5. Reagents 9. Precision None. Precision data are not available for this method. 6. Procedure 6.1 Transfer the entire sample to the plastic sieve. Shake the sieve firmly, washing with a amount of demineralized water as nec­ essary to sieve all material less than 2-mm Subsampling, bottom-material, diameter. coring 6.2 Thoroughly mix the sieved portion, (P-0810-85) returning it to the sample container in which it was received. 6.3 Core the sample, using either a 10-mm 1. Application or a 20-mm glass tube, and place the core 1.1 This method may be used to subsample material (subsample) in a tared container. In wet bottom-material samples for subsequent some cases it may be necessary to withdraw analysis. more than one core in order to have sufficient 1.2 If the amount of material less than 2 mm bottom material for the particular determin­ in size is insufficient for adequate coring, a ation to be made (NOTE 1). Jones-type teflon splitter may be used (method NOTE 1. The type of container and the amount P-0811). of bottom material required will depend on the individual method for which the subsample will 2. Summary of method be used. 2.1 The entire wet sample is sieved, using a 6.4 Weigh the subsample to determine its 2-mm plastic sieve. The material passing wet weight. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 47 6.5 At the same time as the other subsam- 2.3 Care must be taken that the sieved sam­ plings, use the small-bore (10-mm) tube to with­ ple is well mixed and that the percent moisture draw a separate subsample for a moisture determined on the separate subsample reflects determination (method P-0590). the moisture content of the subsample analyzed. 7. Calculations 2.4 In general, when peat-like material com­ Compute the dry weight of a subsample as poses the majority of a sample, it should be con­ follows: sidered as part of the sample even though it will not pass easily through a 2-mm sieve. (Such (100-M) samples are not to be confused with samples Sample, dry weight (g)= W 100 consisting almost solely of leaves and twigs). where 3. Interferences Certain samples, especially those with a large W— wet weight of the sample, grams, proportion of sand-size material, may clog the and Jones-type splitter, which results in an uneven M= percent of moisture as determined by split. method P-0590. 4. Apparatus 8. Report 4.1 Sieve, plastic, with 2-mm openings. See individual determination for the number 4.2 Splitter, Teflon, Jones-type. of significant figures to be reported. 5. Reagents 9. Precision None. Precision data are not available for this method 6. Procedure 6.1 Thoroughly mix the sieved portion and Subsampling, bottom-material, determine the percent moisture (method splitting P-0590) of a subsample obtained by coring with a 10-mm tube (NOTE 1). (P-0811-85) NOTE 1. Alternatively, the moisture content may be determined on one of the last splits; 1. Application however, since samples do not split into equal- 1.1 This method may be used to subsample weight subsamples, the amount of wash water wet bottom-material samples for subsequent used in each split is extremely critical and must analysis if the amount of material that is less be calculated accurately. than 2 mm in size is insufficient for adequate 6.2 Accurately weigh the rest of the sample. coring (method P-0810). 6.3 Pass the sample through a Jones-type 1.2 Samples that clog the splitter may be Teflon splitter. subsampled by coring (method P-0810). 6.4 Accurately weigh the split subsample. 6.5 Using one of the split subsamples, repeat 2. Summary of method steps 6.3 and 6.4 until a sufficient number of 2.1 The entire wet sample is sieved, using a subsamples is available. 2-mm plastic sieve. The material passing through the sieve is subsampled with a Jones- 7. Calculations type Teflon splitter. Compute the dry weight of a split subsample 2.2 The percent moisture is determined by as follows: drying a suitable portion of the sieved wet sam­ ple (method P-0590) in order to compute all (100-M) constituents determined on an oven-dried basis Sample, dry weight (g)=- ^o (105 °C). 100 48 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS where 5. Reagents W-^— wet weight, grams, of the split sub- None. sample, W2= wet weight, grams of the other sub- 6* Procedure sample produced by the splitting, 6.1 Place a subsample of sieved bottom W0~ weight, grams, of the sample before material, between 1 and 2 g, into a crucible that splitting, has been dried in an oven for 1 h at 105 °C, and, cooled, and weighed to the nearest 0.1 mg. M = percent moisture as determined by 6.2 Weigh sample and crucible to the nearest Method P-0590. 0.1 mg. 6.3 Place the crucible containing sample in 8. Report an oven and dry to constant weight at 105 °C. See each individual determination for the number of significant figures to be reported. 7. Calculations W-D Moisture (percent) = ——— XI00 9. Precision W Precision data are not available for this method. where Percent moisture, total in- W— total wet weight of sample, grams, bottom-material, gravimetric and £)= dry weight of sample, grams. (P-0590-85) 8. Report 1. Application Report percentage of moisture to two signif­ 1.1 This method may be used to determine icant figures. the percent moisture in bottom material less 9. Precision than 2 mm in size that has not been air-dried Precision data are not available for this (method P-0810 or P-0811). To determine per­ method. cent moisture of air-dried bottom-material sam­ ples, see method P-0520. 1.2 Information obtained by this method is used to compute the dry weight of subsamples Extraction procedure, bottom- used for analysis of bottom material. The result material obtained is not applicable to bottom material in situ. (1-5485-85) 1. Application 2. Summary of method This method must be used as preliminary A portion of well-mixed sample less than 2 treatment of bottom-material samples to de­ mm in size is dried at 105 °C. The loss of weight stroy organic matter and to desorb and solu- on drying is computed as a percentage of the bilize metals. If it has been determined that total wet weight and represents the percent greater than 95 percent of the substance is moisture of the sample. solubilized, the results should be reported as "total." If less than 95 percent is solubilized, 3. Interferences the results should be reported as "total recover­ None. able." Only that portion of bottom material that passes a 2-mm sieve is taken for analysis. 4. Apparatus 4.1 Crucible, platinum or porcelain. 2. Summary of method 4.2 Desiccator. 2.1 The determination of acid-soluble metals 4.3 Oven, 105 °C. occurring in or associated with sediment and METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 49 bottom material involves (1) destruction and 5.2 Hydrochloric acid, double-distilled, 1M: removal of all organic matter, followed by (2) Add 17 mL of 6M HC1 (double-distilled) to treatment to dissolve acid-soluble substances, demineralized water and dilute to 100 mL with and (3) measurement of the concentration of demineralized water. constituents in the resulting solution. 5.3 Hydrochloric acid, double-distilled, 2.2 Removal or destruction of organic mat­ 0.3M: Add 50 mL of 6M HC1 (double-distilled) ter is a necessary preliminary treatment when to 950 mL demineralized water. acid-soluble metals are to be determined in sam­ 5.4 Hydrogen peroxide solution, (H2O2), ples of bottom material. This is conveniently ac­ 30-percent w/v. complished with a strong oxidizing agent that 5.5 Nitric acid, dilute (1+4): Add 1 volume has only a minimal effect on the mineral compo­ of concentrated HNO3 (sp gr 1.42) to 4 volumes sition of the participate material The following of demineralized water. procedure, employing hydrogen peroxide (H2O2), is generally satisfactory for destroying organic 6. Procedure matter present in samples of bottom material 6.1 Immediately before each use, clean all prior to extraction of acid-soluble metals. glassware used in this determination by rinsing, 2.3 The procedure also provides for a hot, first with warm dilute HNO3 (1+4), and then dilute hydrochloric acid digestion of the sam­ with demineralized water. ple after destruction of organic matter. The 6.2 Weigh, to the nearest milligram, be­ digestion is designed to ensure dissolution of all tween 4 and 10 g of thoroughly homogenized, sorbed metals, as well as of all readily acid- undried sample that has passed a 2-mm non- soluble components of the bottom-material mix­ metallic sieve (method P-0810 or P-0811). Com­ ture, without appreciably attacking the mineral pute the dry weight of the sample by structure of the sediment. The treatment is determining the percent moisture on a separate comparable to the procedure used to desorb and subsample (method P-0590). dissolve soluble metals associated with par- 6.3 Quantitatively transfer each sample to ticulate material present in water-suspended a 600-mL beaker. Add sufficient demineralized sediment samples (method 1-3485). water to provide a volume ratio of water to sam­ ple between 1:1 and 2:1. Cover the beaker with 3. Interferences a ribbed watchglass. There are no interferences in the acid 6.4 Check the acidity of the solution with lit­ digestion. mus paper. Make acidic by the dropwise addi­ tion of lAf HC1, if necessary. 4. Apparatus 6.5 Add 30-percent H202 in increments of Filter paper, Whatman No. 41 or equivalent. about 5 mL, stir the suspension, and allow time for any strong effervescence or frothing to sub­ 5. Reagents side. Continue adding H2O2 in small amounts 5.1 Hydrochloric acid, double-distilled, 6M; until the sample ceases to froth. Add a specified volume of reagent-grade concen­ NOTE 1. A demineralized water blank must be trated HC1 (sp gr 1.19) to an equal volume of carried through the procedure. Add equivalent demineralized water. Purify this acid by double amounts of 30-percent H2O2 and acid to the distillation, retaining only the middle one-half blank. of the total volume of acid being distilled in each 6.6 Place the sample beaker on a steam bath case. Collect the distillate in a clean polyethyl­ or hotplate at low heat (65 to 70 °C), and observe ene or Teflon reagent bottle and protect the it closely until certain that all danger of further purified acid from contamination. The concen­ strong reaction has passed. Continue to add tration of the distillate will be approx 6M. Dou­ small increments of H2O2 until all organic mat­ ble distillation of HC1 may be omitted if each ter is destroyed, as evidenced by absence of any lot of acid is analyzed prior to use and is deter­ dark-colored material and lack of noticeable mined to yield a negligible blank for all metals frothing. Evaporate excess liquid between ad­ of interest. ditions of H2O2 to keep the water-to-sediment 50 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS ratio between 1:1 and 2:1. Do not allow the mix­ for metals by atomic absorption spectrophoto ture to evaporate to dryness at any time. metric or other appropriate methods. 6.7 Dilute the mixture to 200 mL with 2.2 For additional information on principles demineralized water. of the methods, see individual methods for each 6.8 Add 10 mL double-distilled HCI, 6M, of the substances. mix thoroughly, and heat on a hotplate to just below boiling. Continue heating for 30 min. 3. Interferences 6.9 Filter the hot mixture (Whatman No. 41 There are no interferences in the acid filter paper, or equivalent) and collect the digestion. filtrate in a 250-mL volumetric flask. Wash the residue on the filter paper at least three times 4. Apparatus with hot 0.3M HC1. Filter paper, Whatman No. 41 or equivalent. 6.10 Cool the filtrate to room temperature, and dilute to volume with demineralized water, 5. Reagents and mix thoroughly. 5.1 Hydrochloric acid, double-distilled, 6M: 6.11 Use appropriate aliquots of this solu­ Add a specified volume of reagent-grade concen­ tion to determine acid-soluble metals as re­ trated HC1 (sp gr 1.19) to an equal volume of quired. demineralized water. Purify this acid by double distillation, retaining only the middle one-half 7. Calculations of the total volume of acid being distilled in each See individual method for each metal. case. Collect the distillate in a clean polyeth­ ylene or Teflon reagent bottle and protect the 8. Report purified acid from contamination. The concen­ See individual method for significant figures tration of the distillate will be approx 6M. to be reported. Double distillation of HC1 may be omitted if each lot of acid is analyzed prior to use and is 9. Precision determined to yield a negligible blank for all See individual method for each metal. metals of interest. 5.2 Hydrochloric acid, double-distilled, 0.3Af: Add 50 mL of 6Af HC1 (double-distilled) Extraction procedure, water- to 950 mL demineralized water. suspended sediment 5.3 Nitric acid, dilute (1+4): Add 1 volume (1-3485-85) of concentrated HNO3 (sp gr 1.42) to 4 volumes of demineralized water. 1. Application This method must be used as preliminary 6. Procedure treatment of samples of water-suspended sedi­ 6.1 Immediately before each use, clean all ment to desorb and solubilize metals associated glassware used in this procedure by rinsing, with the suspended sediment phase of the sam­ first with warm dilute HNO3 (1+4) and then ple. If it has been determined that greater than with demineralized water. 95 percent of the substance to be determined 6.2 Mark the level of the sample on the is solubilized, the results should be reported as bottle and determine the volume by weight. "total." If less than 95 percent is solubilized, 6.3 Transfer the entire contents of the sam­ the results should be reported as "total ple bottle to a beaker or fleaker. recoverable." 6.4 Add 5 mL double-distilled 6Af HC1 to the sample bottle for each 100 mL of original sam­ 2. Summary of method ple. Shake vigorously and add this solution to 2.1 The sample is digested by heating with the beaker. Heat solution in beaker to just dilute hydrochloric acid. Following digestion, below boiling and continue heating until the the sample is filtered to remove particulate volume is reduced approximately 20 percent matter, and aliquots of the filtrate are analyzed (NOTE 1). METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 51 NOTE 1. A demineralized water blank must be Total decomposition, sediment carried through the procedure. Add an equiva­ lent amount of acid to the blank. (1-5473-85) 6.5 Filter the hot mixture (Whatman No. 41 (1-5474-85) filter paper or equivalent) into the original (1-5475-85) sample bottle. Wash the residue on the filter 1. Application paper three times with 5-mL portions of hot LI These methods may be used to analyze sus­ 0.3M HCL pended and bottom sediment for the determina­ 6.6 Cool to room temperature, and dilute to tion of total concentration of constituents present the original volume with demineralized water. 1.2 Analyses must be performed on dried Mix thoroughly. and ground samples that either have been fused 6.7 Use appropriate aliquots of this solution with a lithium metaborate-lithium tetraborate to determine acid-soluble metals as required. flux with the resulting bead dissolved in acidi­ fied deionized water or have been solubilized 7. Calculations with a combination of nitric, hydrofluoric, and See individual method for each metal. perchloric acids heated in open teflon beakers. 2. Summary of method 8. Report 2.1 See method 1-5473, metals, major, total See individual method for significant figures in sediment; method 1-5474, metals, major and to be reported. minor, total in sediment; and method 1-5475, metals, minor, total in sediment, for complete 9. Precision solubilization procedures. See individual method for each metal. 2.1 After solubilization the solutions are analyzed by atomic absorption spectrometry.

Analytical methods

Acidity, electrometric titration

Parameters and Codes: Acidity, 1-1020-85 (mg/L as H + 1): 71825 (mg/L as CaCOg): 00435

1. Application to avoid unnecessary agitation of the sample. This method is applicable to many acidic sam­ A tightly capped bottle is essential for storing ples. When the sample is suspected or known and transporting samples. The determination to contain mostly weak acids, however, the con­ should be performed at the time of sampling for struction of a neutralization curve is imperative, greatest accuracy. and the acidity value is reported and interpreted in terms of the character of the curve obtained. 4. Apparatus 4.1 Buret, 50-mL capacity. 2. Summary of method 4.2 Hotplate. 2.1 Acidity is determined by titrating the 4.3 pH meter. sample with a standard solution of a strong 4.4 Stirrer, magnetic. base to an electrometricaUy observed end point pH of 8.3. The titration is carried out at room temperature, except that the sample is heated 5. Reagents briefly near the end of the titration to increase 5.1 Sodium hydroxide stock solution) ap- the rate of hydrolysis of metal ions present. prox. 2N: Dissolve 80 g NaOH in carbon diox­ 2.2 For additional information concerning ide-free water and dilute to 1 L with carbon the determination of acidity and for instructions dioxide-free water. Store in a tightly capped for constructing an electrometric titration polyethylene bottle. curve, see ASTM Method D 1067-82, "Stand­ 5.2 Sodium hydroxide standard solution, ap- ard Methods of Test for Acidity or Alkalinity prox. Q.025N: Dilute 12.5 mL 2N NaOH with of Water," (American Society for Testing and carbon dioxide-free water to approx 1 L. Stand­ Materials, 1984). ardize the solution against primary standard potassium hydrogen phthalate (KHC8H4O4) as 3. Interferences follows: Lightly crush 3 g of the salt to a Dissolved gases that are acidic, such as CO2 fineness of approx 100 mesh and dry for at least and H2S, may easily be lost from the sample. 1 h at 110°C. Dissolve about 2 g, accurately If any substantial part of the acidity is due to weighed to the nearest milligram, in carbon gaseous solutes, special care must be taken to dioxide-free water and dilute to 500.0 mL. prevent their escape prior to and during the Titrate 50.0 mL of the solution with the NaOH titration. Gases are less soluble in warm water standard solution to pH 8.6: than in cold; hence, the sample must be kept chilled until analyzed, and even then the analysis must be performed as soon as possible. Normality of NaOH = Stirring and agitation of the sample cause ex­ g KHC8H4O4 in 50.0 mL X 4.896 pulsion of dissolved gases; care must be taken mLNaOH

53 54 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6. Procedure 7.3 Determine acidity as CaCO3 in mg/L as 6.1 Samples should be collected in tightly follows: capped polyethylene bottles, with as little agi­ tation as possible, particularly if it is suspected Acidity, mg/L as CaCO3= or known that any significant part of the acid­ mL6 XNbX103 X50.05 ity is due to dissolved gases. Chill or otherwise mLs keep the sample cool during transportation to the laboratory and perform the determination where as soon as possible. Do not open the sample bot­ mL6 and mLs=volumes of standard NaOH tle until ready to determine the acidity, and solution and sample, respec­ then perform the determination without delay tively, once the bottle has been opened. and 6.2 Carefully pipet an aliquot of sample con­ Nt=normality of standard NaOH solution. taining less than 1.0 mg H+1 (50.0 mL max) into a 150-mL beaker. Avoid disturbing any 8. Report sediment in the sample bottle. Do not filter. 8.1 Report acidity values in milliequivalents per liter or milligrams per liter as hydrogen ion 6.3 Insert the beaker in the titration as follows: less than 10 me/L (mg/L), one deci­ assembly and record the pH. mal; 10 me/L (mg/L) and above, two significant 6.4 Titrate the sample with standard NaOH figures. solution to pH 8.3. 8.2 Report acidity, hydrogen ion (71825), 6.5 Heat the solution to about 90 °C (do not concentrations as milligrams per liter. boil), and maintain this temperature for 2 min. 8.3 Report acidity, calcium carbonate 6.6 Cool to room temperature and resume (00435), concentrations in milligrams per liter the titration, titrating again to a final pH of 8.3. as follows: less than 100 mg/L, whole numbers; Record the total volume of titrant used (mLb). 100 mg/L and above, two significant figures. 9. Precision 7. Calculations The precision for one sample expressed in 7.1 Determine acidity as me/L as follows: both standard deviation and percent relative standard deviation is as follows: jL Acidity, me/L= — * XNfeX103 Standard Relative standard mL Number of Mean deviation deviation laboratories (mg/L as H"+1,1"1)

Parameter and Code: Alkalinity, 1-1030-85 (mg/L as CaCCg: 00410

1. Application point may be determined for each sample by This method is suitable for analyzing water adding the titrant in small increments in the with any amount of alkalinity, but aliquots for vicinity of pH 4.5 and by recording the pH of analysis should be taken to avoid a titration the solution after each measured addition. The volume of standard acid in excess of 50 mL. true end point is then determined from either (1) a plot of pH versus total titrant volume, 2. Summary of method where the end point is the pH corresponding to 2.1 Alkalinity is determined by titrating the a change in slope of the curve, or (2) a plot of water sample with a standard solution of strong acid. The end point of the titration is selected SpH versus titrant volume as pH 4.5. AmL titrant 2.2 For waters that contain only small quan­ tities of dissolved mineral matter, the alkalinity where the end point is that volume at which determination is likely the largest single source there occurs a maximum rate of change of pH of error in the analysis. Alkalinity is very sus­ per volume of titrant added. ceptible to change between time of collection 2.4 There are other methods for arriving at and analysis, with changes occurring more a more reliable determination of total alkalin­ rapidly after the sample bottle is opened. The ity. Barnes (1964) discusses the several factors overall alkalinity value is probably somewhat involved in the accurate measurement of alka­ more stable than the relative values of the com­ linity, particularly under field conditions. A mon alkalinity components. Unless a gross error routine laboratory method for determining total is made in the initial determination of alkalini- alkalinity with improved accuracy for widely ty, it is seldom advisable to try to check the differing types of water has been described by results if several days have elapsed since the Larson and Henley (1955) and further evaluated bottle was first opened. The alkalinity of some by Thomas and Lynch (1960). A rather complete samples may change appreciably in a few hours. consideration of carbonate equilibria and their The determination should be performed at the analytic considerations may be found in a time of sampling for highest accuracy. publication by Stumm and Morgan (1970). 2.3 Selection of pH 4.5 as the titration end point for determining total alkalinity is ar­ 3. Interferences bitrary and corresponds to the true equivalence 3.1 Any ionized substance that reacts with point only under ideal conditions. The equiva­ a strong acid can contribute to alkalinity if the lence point of the bicarbonate-carbonic acid reaction occurs at a pH above that of the speci­ titration varies with the concentration of bicar­ fied end point; examples are salts of weak bonate present; the deviation from pH 4.5 is organic and inorganic acids. particularly serious at low bicarbonate-ion con­ 3.2 Oils and greases, if present, may tend to centrations. When greater accuracy in the deter­ foul the pH-meter electrode and prevent its mination is needed, the titration equivalence proper operation.

55 56 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 4. Apparatus where 4.1 Buret, 50-mL capacity. 4.2 pH meter. mLa and mL5=volumes of standard acid and 4.3 Stirrer, magnetic. sample, respectively.

5. Reagents 8. Report 5.1 Sodium carbonate standard solution, 1.0 Report alkalinity, total (00410), concentra­ mL o 1.00 mg HCO^1: Dry 1.0 g primary stand­ tions as follows: less than 1,000 mg/L, whole ard Na2CO3 at 150 to 160 °C for 2 h. Cool in a numbers; 1,000 mg/L and above, three signifi­ desiccator and dissolve 0.8685 g in carbon diox­ cant figures. ide-free water; dilute to 1,000 mL. 5.2 Sulfuric acid standard solution, 0.01639AT, 9. Precision 1.00 mL o 1.00 mg HCOjj1: Cautiously add 0.5 9.1 Precision for alkalinity for 36 samples mL concentrated H2SO4 (sp gr 1.84) to 950 mL within the range of 3.6 to 316 mg/L calcium car­ water. (The titrant is stable for several months bonate may be expressed as follows: if protected from ammonia fumes and is usually prepared in larger quantities.) After the solution has been thoroughly mixed, standardize by titrat­ 1.93 ing 25.00 mL NaoCO3 standard solution (1.00 mL o 1.00 mg HCOgi) to pH 4.5. Adjust the concen­ where tration of the sulfuric acid standard solution to exactly 0.01639W by dilution with water or by ST= overall precision, milligrams per liter, addition of dilute acid as indicated by the first ti- and tration. Confirm the exact normality by restand- X— concentration of alkalinity as CaCO3, ardization. Although the sulfuric acid standard milligrams per liter. solution is reasonably stable, its normality should be verified at least monthly (NOTE 1). The correlation coefficient is 0.5308. NOTE 1. Preparing standard sulfuric acid that 9.2 Precision for alkalinity for six of the 36 is not exactly 0.01639AT may be more conven­ samples expressed in terms of the percent ient. Standard sulfuric acid that is approximate­ relative standard deviation is as follows: ly 0.016397V (but the exact normality of which Relative standard is known) can be used if the appropriate factor Number of Mean {mg/L deviation is applied in the calculations. laboratories as CaCO^ (percent) 25 3.6 25 6. Procedure 14 56.7 11 6.1 Water samples for the determination of 27 107 13 31 119 3 alkalinity should not be filtered, diluted, concen­ 30 183 6 trated, or altered in any way. The determination 26 316 2 should be performed without delay after the sample bottle has been opened. 6.2 From a settled, unfiltered sample, pipet a volume containing less than 40 mg alkalinity References as HCOjj1 (50.0 mL max) into a suitable beaker. Barnes, Ivan, 1964, Field measurement of alkalinity and pH: 6.3 Titrate immediately with 0.01639AT U.S. Geological Survey Water-Supply Paper 1535-H, H2SO4 and record the titrant volume at pH 4.5. 17 p. Larson, T. E.t and Henley, Laurel, 1955, Determination of 7. Calculations low alkalinity or acidity in water Analytical Chemistry, v. 27, p. 851-2. Total alkalinity as CaCO3 in mg/L= Stumm, Werner, and Morgan, J. J., 1970, Aquatic Chemis­ try: New York, John Wiley and Sons, 583 p. 1,000 Thomas, J. F. J., and Lynch, J. J., I960, Determination of X0.8202X(mLa to pH 4.5) carbonate alkalinity in natural waters: American Water mLc Works Association Journal, v. 52, p. 259-68. Alkalinity, electrometric titration, automated

Parameter and Code: Alkalinity, 1-2030-85 (mg/L as CaCOg): 00410

1. Application quantities.) After the solution has been This method is suitable for analyzing water thoroughly mixed, standardize by titrating with any amount of alkalinity. Sample aliquots 25.00 mL Na2CO3 standard solution (1.00 mL for analysis and maximum titration volume of o 1.00 mg HCOg1) to pH 4.5. Adjust the standard acid will depend on specifications in concentration of the sulfuric acid standard solu­ the manufacturer's instruction manual. tion to exactly 0.01639ATby dilution with water or by addition of dilute acid as indicated by the 2. Summary of method first titration. Confirm the exact normality by 2.1 Alkalinity is determined by titrating the ^standardization. Although the sulfuric acid water sample with a standard solution of a standard solution is reasonably stable, its nor­ strong acid. The end point of the titration is se­ mality should be verified at least monthly lected as pH 4.5. (NOTE 1). 2.2 For additional information on the prin­ NOTE 1. Preparing standard sulfuric acid that ciples of the method see alkalinity (1-1030). is not exactly 0.01639AT may be more conven­ ient. Standard sulfuric acid that is approximate­ 3. Interferences ly 0.016397V (but the exact normality of which See alkalinity (1-1030). is known) can be used if the appropriate factor is applied in the calculations. 4. Apparatus 4.1 Automatic titrator, with potentiometric 6. Procedure 6.1 Water samples for the determination of assembly. alkalinity should not be filtered, diluted, concen­ 4.2 Combination electrode (glass and refer­ trated, or altered in any way. The determination ence). Separate glass and reference electrodes should be performed without delay after the are also satisfactory. sample bottle has been opened. 6.2 Set up the automatic titrator according 5. Reagents to the directions given in the instruction 5.1 Sodium carbonate standard solution, manual. 1.00 mL o 1.00 mg HCOjj1: Dry 1 g primary 6.3 From a settled, unfiltered sample, trans­ standard Na2CO3 at 150 to 160 °C for 2 h. Cool fer or pipet a volume of sample to the vessel in a desiccator and dissolve 0.8685 g in carbon specified by the manufacturer. dioxide-free water; dilute to 1,000 mL. 6.4 Set the end point to pH 4.5 following the 5.2 Sulfuric acid standard solution, instructions provided with the instrument. 0.01639AT, 1.00 mL o 1.00 mg HCOg1: Cau­ 6.5 Place the samples in position in the titra­ tiously add 0.5 mL concentrated H2SO4 (sp gr tion assembly and activate the automatic poten­ 1.84) to 950 mL water. (The titrant is stable for tiometric titration, using 0.01639AT H2SO4 as several months if protected from ammonia titrant. Continue titrations until all samples fumes, and it is usually prepared in larger have been titrated. 57 58 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 7. Calculations 9* Precision 9.1 The standard deviation for alkalinity Total alkalinity as CaCO3 (mg/L)= within the range of 18.4 to 303 mg/L for 17 sam­ ples was found to be independent of concentra­ 1,000 tion. The 95-percent confidence interval for the X0.8202X(mLa to pH 4.5) average standard deviation of 6.7 mg/L ranged from 5.8 to 7.9 mg/L. where 9.2 Precision for alkalinity for five of the 17 samples expressed in terms of percent relative mLa and mLs= volumes of standard acid and standard deviation is as follows: sample, respectively. Number of Mean {mg/L Relative std. deviation 8. Report laboratories asCaCO3) ____(percent)____ Report alkalinity, total (00410), concentra­ 7 18.4 13 tions as follows: less than 1,000 mg/L, whole 3 101 17 3 101 2 numbers; 1,000 mg/L and above, three signifi­ 5 151 12 cant figures. 10 303 2 Aluminum, atomic emission spectrometric, d-c plasma

Parameters and Codes: Aluminum, dissolved, 1-1054-85 (jig/L as Al): 01106 Aluminum, total recoverable, I-3054-85 (jig/L as Ai): 01105 Aluminum, suspended recoverable, I-7054-85 (/ig/L as Al): 01107

1. Application 4. Apparatus 1.1 This method may be used to analyze fin­ 4.1 Spectrometer, Spectrometrics, Spectro- ished water, natural water, industrial water, and span IV with d-c argon plasma or equivalent, water-suspended sediment containing from 10 with Echelle optics, printer, autosampler, and to 1000 figIL of aluminum. Samples containing periastaltic pump. more than 1000 jig/L aluminum and (or) with 4.2 Refer to manufacturer's manual to op­ specific conductances greater than 10,000 timize instrument for the following: pS/cm need to be diluted. Plasma viewing position +1 (fig. 9) 1.2 Suspended recoverable aluminum is Gas —————————— Argon calculated by subtracting dissolved aluminum Sleeve pressure ———— 50 psi from total recoverable aluminum. Nebulizer pressure — 25 psi 1.3 Total recoverable aluminum in water- Entrance slit -: ———— 25X300 /on suspended sediment needs to undergo a prelim­ Exit slit ——— ————— 50X300 jim inary digestion-solubilization by method 1-3485 Voltage ———————— 1000 V before being determined. Wavelength —————— 308.215 nm Signal amplification — 40- to 60-pei> 2. Summary of method cent full-scale Aluminum is determined by a direct-reading (1000 emission spectrometer which utilizes a d-c argon 5. Reagents plasma as an excitation source (Johnson and 5.1 Aluminum standard solution /, 1 mL= others, 1979 a,b, 1980). A mixture of lithium 100 fig Al: Dissolve 0.100 g aluminum powder chloride, sulfuric acid, and glycerin is added to in a minimun of 6M HC1 using a Tfeflon beaker. samples and standards to provide a common Heat to increase rate of dissolution. Add 10.0 background matrix and to compensate for vis­ mL 6M HC1 and dilute to 1,000 mL with cosity changes. The liquid mixture is then con­ demineralized water. Store in plastic bottla verted by a ceramic nebulizer into a fine aerosol Excitation and introduced into the plasma via a plastic region spray chamber and Pyrex injection tube. Alu­ minum is determined on the basis of the average of two replicate exposures, each of which is per­ formed on a 10-second integrated intensity. Calibration is performed by standardization -1 with a high-standard solution and a blank.

3. Interferences Plasma Stray-light effects in a high-resolution, single-element d-c argon plasma emission spec­ trometer are negligible. Figure 9.—Plasma position on entrance slit for aluminum 59 60 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Aluminum standard solution II, 1.00 7. Calculations mL=10.0 fig Al: Dilute 100.0 mL aluminum The computer system is designed so that the standard solution I to 1000 mL with demineral- blank and the 1,000 /tg/L of aluminum standard ized water. Store in plastic bottle. are used to establish a two-point calibration curve 5.3 Aluminum working standard, 1.00 mL= The system will convert instrument intensity 1.00 Mg AL* Dilute 100.0 mL aluminum standard readings to analytical concentrations. The printer solution II to 1000 mL with demineralized water. display includes the blank and working-standard Store in plastic bottle instrument intensity readings, blank and stand­ 5.4 Glycerin, USE ard concentrations, sample instrument intensity 5.5 Hydrochloric acid, concentrated (sp gr readings, sample concentrations, average of sam­ 1.19), Ultrex or equivalent. ple concentrations, and standard deviation. 5.6 Hydrochloric acid, 6Af: Add 500 mL con­ centrated HC1 (sp gr 1.19) to 400 mL demineral­ 8. Report ized water and dilute to 1 L with demineralized Report aluminum, dissolved (01106), total- water. recoverable (01105), and suspended-recoverable 5.7 Lithium chloride, LiCl, reagent-grade (01107), concentrations as follows: less than 100 5.8 Matrix modifier: Dissolve 367 g LiCl in /ig/L, nearest 10 /*g/L; 100 ptg/L and above, two 1,000 mL demineralized water. Allow the solution significant figures. to cool Transfer to a 4-L polyethylene container, and add with stirring 2,000 mL of glycerin. In a 9. Precision Tfeflon beaker slowly add with stirring 400 mL 9.1 Precision, based on 14 to 18 determin­ concentrated H2SO4 to 400 mL demineralized ations by a single operator during a 47-day period, water. When the dilute acid has reached room expressed in terms of standard deviation and per­ temperature, add the acid slowly, with stirring, to cent relative standard deviation, is as follows: the glycerin-LiCl mixture Dilute to 4,000 mL with demineralized water. Relative Number of Mean Standard deviation standard deviation 5.9 Sulfuric acid, concentrated (sp gr 1.84), determinations 0*9/M 0*g/U (percent) Ultrex or equivalent. 17 12.9 1.9 14.7 14 30.5 3.0 9.8 6. Procedure 14 73.1 8.9 12.2 6.1 Pipet 10.0 mL sample into a disposable 15 132 11 8.3 18 221 6.0 2.7 plastic test tube 18 437 18 4.1 6.2 Pipet 100 mL demineralized-water blank 18 763 32 4.2 and working standard into plastic bottles. 6.3 Add 2.0 mL matrix modifier to the sample 9.2 It is estimated that the percent relative and 20.0 mL to the blank and working standard. standard deviation for total recoverable and 6.4 Place plastic caps on the tube and bottles suspended recoverable aluminum will be greater and mix well than that reported for dissolved aluminum. 6.5 Refer to manufacturer's manual for computer-operating and wavelength-optimization procedures. Use the prepared blank and aluminum References working standard for instrument calibration and all subsequent recalibrations. Johnson, G. W., Tfeylor, H. E., and Skogerboe, R K, 1979a, Determination of trace elements in natural waters by the 6.6 Refer to manufacturer's manual for auto- D.C argon-plasma, multielement atomic emission spec­ sampler-operating procedures. Pour samples in trometer (DCP-MAES) technique: Spectrochimica Acta, v. autosampler tray, positioning a blank and work­ 34B, p. 197-212. ing standard after every 3 samples for recali- ___1979b, Evaluation of spectral interferences associated bration. Begin analysis (NOTE 1). with a direct current plasma-multielement atomic emis­ NOTE 1. Because of thermal instability inherent sion spectrometer (DCP-MAES) system: Applied Spec- troscopy, v. 33, p. 451-456. with the high-resolution spectrometer, repeak the ___1960, Characterization of an interelement enhancement analytical line if the aluminum standard drifts effect in a dc plasma pt/OTMC emission spectzometry system! more than 3 percent. Applied Spectroscopy, v. 34, pi 19-24. Aluminum, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Aluminum, dissolved, 1-1052-85 (/*g/L as Al): 01106 Aluminum, total recoverable, I-3052-85 (/*g/L as Al): 01105 Aluminum, suspended recoverable, I-7052-85 (jig/L as Al): 01107

1. Application 3.3 Magnesium, as little as 25 mg/L, forms 1.1 This method may be used to analyze an insoluble chelate with 8-hydroxyquinoline at water, brines, and water-suspended sediment pH 8.0 and tends to coprecipitate aluminum containing from 10 to 1,000 /ig/L of aluminum. 8-hydroxyquinolate. However, the magnesium Samples containing more than 1,000 jig/L 8-hydroxyquinolate forms rather slowly (approx should either be diluted prior to chelation- 4 to 6 min); its interference can be avoided if the extraction or be analyzed by the atomic absorp­ aluminum 8-hydroxyquinolate is extracted with tion spectrometric direct method. MIBK immediately after the sample is buffered 1.2 Suspended recoverable aluminum is to pH 8. calculated by subtracting dissolved aluminum from total recoverable aluminum. 4. Apparatus 1.3 Total recoverable aluminum in water- 4.1 Atomic absorption spectrometer suspended sediment needs to undergo prelim­ equipped with electronic digital readout and inary digestion-solubilization by method 1-3485 automatic zero and concentration controls. before being determined. 1.4 If the iron concentration of the sample ex­ 4.2 Refer to the manufacturer's manual to optimize instrument for the following: ceeds 10,000 /ig/L, determine aluminum by the Grating ———————— Ultraviolet atomic absorption spectrometric direct method. Wavelength ————— 309.3 nm 2. Summary of method Source (hollow-cathode lamp) —————— Aluminum 2.1 Aluminum is determined by atomic ab­ Burner —————— sorption spectrometry following chelation with Nitrous oxide 8-hydroxyquinoline and extraction with methyl Oxidant ———————— Nitrous oxide Fuel —————————— Acetylene isobutyl ketone (MIBK). The extract is aspi­ rated into the nitrous oxide-acetylene flame of Type of flame ———— Fuel-rich the spectrometer. 2.2 Additional information about the prin­ 5. Reagents ciples of the method may be found in Snell and 5.1 Aluminum standard solution /, 1.00 SneU (1959), and in Fishman (1972). mL=100 /ig Al: Dissolve 0.100 g Al powder in a minimun of 6M HC1. Heat to increase rate of 3. Interferences dissolution. Add 10.0 mL 6M HC1 and dilute to 3.1 Concentrations of iron greater than 1000 mL with demineralized water. 10,000 /ig/L interfere by suppressing aluminum 5.2 Aluminum standard solution II, 1.00 absorption. mL=1.00 fig Al: Dilute 10.0 mL aluminum 3.2 Manganese concentrations as great as standard solution I and 1 mL concentrated 80,000 figlL do not interfere if the turbidity in HNO3 (sp gr 1.41) to 1,000 mL with demineral­ the MIBK extract is allowed to settle (prefer­ ized water. This standard is used to prepare ably overnight). working standards at the time of analysis. 61 62 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Ammonium hydroxide-ammonium ace­ dissolved or total recoverable aluminum in each tate buffer solution: Dissolve 200 g NH4C2H3O2 sample from the digital display or printer while and 70 mL concentrated NH4OH (sp gr 0.90) in aspirating each sample Dilute those samples water, and dilute to 1 L with demineralized water. containing concentrations of aluminum that ex­ 5.4 8-Hydroxyquinoline solution: Dissolve 20 ceed the working range of the method; repeat the g 8-hydroxyquinoline in 57 mL glacial acetic acid chelation-extraction and multiply by the proper (sp gr 1.06) and in 200 mL demineralized water, dilution factors. and dilute to 1 L with demineralized water. 7.2 Tb determine micrograms per liter of 5.5 Methyl isobutyl ketone (MIBK). suspended recoverable aluminum, subtract dis- solved-aluminum concentration from total- 6. Procedure recoverable-aluminum concentration. 6.1 Clean all glassware used in this determin­ ation with warm, dilute HNO3 (1+9) and rinse with demineralized water immediately before us& 8. Report 6.2 Pipet a volume of sample solution con­ Report aluminum, dissolved (01106), total- taining less than 100 jig Al (100 mL max) into recoverable (01105), and suspended-recoverable a 200-mL volumetric flask and adjust the volume (01107), concentrations as follows: less than 100 to approx 100 mL. pgfL, nearest 10 jig/L; 100 j*g/L and above, two 6.3 Prepare a blank and at least six standards significant figures. and adjust the volume of each to approx 100 mL with demineralized water. 9. Precision 6.4 Add 2 mL 8-hydroxyquinoline solution 9.1 The standard deviation for dissolved alu­ and mix (NOTE 1). minum within the range of 74 to 793 /ig/L for 10 NOTE 1. Proceed to paragraph 6.5 if only dis­ samples was found to be independent of solved aluminum is to be determined. If total concentration. The 95-percent confidence inter­ recoverable aluminum is to be determined, add val for the average standard deviation of 58.5 2.2 mL concentrated NH4OH (sp gr 0.90) to the /zg/L ranged from 47.8 to 77.0 /*g/L. sample solutions that undergo digestion-solubili- 9.2 Precision for dissolved aluminum for six zation (paragraph 1.3), and then proceed to of the 10 samples expressed in terms of the per­ paragraph 6.5. cent relative standard deviation is as follows: 6.5 Add 10 mL NH4OH-NH4C2H3O2 buffer solution to one sample and immediately add 10.0 Relative standard Number of Mean deviation mL MIBK. Shake vigorously for 15 sec. Each laboratories WU (percent) sample must be treated individually to avoid in­ 6 74 15 terference from magnesium. Each remaining 4 82 37 sample, blank, and standard is treated in a like 4 195 9 manner. 4 252 29 5 650 23 6.6 Allow the layers to separate and add 3 793 3 demineralized water until the ketone layer is com­ pletely in the neck of the flask (NOTE 2). NOTE 2. If the layers do not separate, allow to 9.3 It is estimated that the percent relative stand overnight. standard deviation for total recoverable and 6.7 Aspirate the ketone layer of the blank to suspended recoverable aluminum will be greater set the automatic zero control Use the automatic than that reported for dissolved aluminum. concentration control to set the concentrations of standards. Use at least six standards. Cali­ brate the instrument each time a set of samples References is analyzed and check calibration at reasonable intervals, Fishman, M. JM 1972, Determination of aluminum in water Atomic Absorption Newsletter, v. 11, p. 46-47. Snell, F. D., and Snell, G X, 1959, Colorimetric methods of 7. Calculations analysis: Princeton, D. Van Nostrand Company, 7.1 Determine the micrograms per liter of p, 181-183. Aluminum, atomic absorption spectrometric, direct

Parameters and Codes: Aluminum, dissolved, 1-1051-85, fcg/l as Al): 01106 Aluminum, total recoverable, 1-3051-85 fog/L as Al): 01105 Aluminum, suspended recoverable 1-7051-85 (pg/L as Al): 01107 Aluminum, recoverable-from-bottom-material, dry wt, 1-5051-85 0*9/9 as Al): 01108

1. Application 3. Interferences 1.1 This method may be used to analyze 3.1 Aluminum ionizes slightly in the nitrous water and water-suspended sediment contain­ oxide-acetylene flame; to control this effect, ad­ ing at least 100 jig/L of aluminum. Sample solu­ just the sodium-ion concentration of each stand­ tions containing more than 5,000 j*g/L need ard and sample to at least 850 mg/L. either to be diluted or to be read on a less ex­ 3.2 Individual concentrations of sodium panded scale. Sample solutions containing less (9,000 mg/L), potassium (9,000 mg/L), calcium than 100 /*g/L and brines need to be analyzed (4,000 mg/L), magnesium (4,000 mg/L), sulfate by the atomic absorption spectrometric chela- (9,000 mg/L), chloride (9,000 mg/L), nitrate tion-extraction method, provided that the in­ (9,000 mg/L), and iron (9X106 Mg/L) do not in­ terference limits discussed in that method are terfere. Greater concentrations of each constit­ not exceeded. uent were not investigated* 1.2 Suspended recoverable aluminum is calculated by subtracting dissolved aluminum 4. Apparatus from total recoverable aluminum. 4.1 Atomic absorption spectrometer 1.3 This method may be used to analyze bot­ equipped with electronic digital readout and tom material containing at least 5 /xg/g of automatic zero and concentration controls. aluminum. 4.2 Refer to the manufacturer's manual to 1.4 Total recoverable aluminum in water- optimize instrument for the following: suspended sediment needs to undergo prelim­ Grating ——————— Ultraviolet inary digestion-solubilization by method Wavelength ————— 309.3 nm 1-3485, and recoverable aluminum in bottom Source (hollow- cathode lamp) —— Aluminum materials needs to undergo preliminary Burner ———————— Nitrous oxide digestion-solubilization by method 1-5485 Oxidant ——————— Nitrous oxide before being determined. Fuel ————————— Acetylene Type of flame ———— Fuel-rich 2. Summary of method Aluminum is determined by atomic absorp­ 5. Reagents tion spectrometry by direct aspiration of the 5.1 Aluminum standard solution, 1.00 mL= sample into a nitrous oxide-acetylene flame 100 jig Al: Dissolve 0.100 g Al powder in a without preconcentration or pretreatment of the minimum of 6Af HC1. Heat to increase rate of sample other than the addition of sodium dissolution. Add 10.0 mL 6M HCL and dilute chloride to control ionization of aluminum, to 1,000 mL with demineralized water. and bis(2-ethoxyethyl)ether to enhance the 5.2 Aluminum working standards, Prepare analytical sensitivity (Ramakrishna and others, at least six working standards containing from 1967). 100 to 5,000 Mg/L of Al by appropriate dilution 63 64 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS of aluminum standard solution. Add 1.0 mL 8.2 Report aluminum, recoverable from bot­ NaCl solution and 1.0 mL bis(2-ethoxyethyl)- tom material (01108), concentrations as follows: ether for each 10 mL of working standard. less than 1,000 /ig/g, nearest 10 jtg/g; 1*000 /ig/g Prepare fresh daily. and above, two significant figures. 5.3 Bis(2-ethoxyethyl)ether. Eastman Kodak Co. Chemical No. 4738 or equivalent. 9. Precision 5.4 Sodium chloride solution, 25.4 g/L: 9.1 Precision for dissolved aluminum for 17 Dissolve 25.4 g NaCl in demineralized water and samples within the range of 40 to 811 /tg/L, may dilute to 1 L. be expressed as follows:

6. Procedure Sr=0.253X + 9.84 6.1 Add 1.0 mL NaCl solution and 1.0 mL bis(2-ethoxyethyl)ether to 10.0 mL of sample where solution and mix thoroughly. ST= overall precision, micrograms per liter, 6.2 Aspirate the blank to set the automatic and zero control. Use the automatic concentration X= concentration of aluminum, micrograms control to set the concentrations of standards. per liter. Use at least six standards. Calibrate the instru­ The correlation coefficient is 0.7779. ment each time a set of samples is analyzed and 9.2 Precision for dissolved aluminum for six check calibration at reasonable intervals. of the 17 samples expressed in terms of the per­ cent relative standard deviation is as follows: 7. Calculations 7.1 Determine the micrograms per liter of Number of Mean Relative standard deviation dissolved or total recoverable aluminum in each laboratories {percent) sample from the digital display or printer while 7 40 135 7 40 85 aspirating each sample. Dilute those samples 5 138 79 containing concentrations of aluminum that ex­ 8 144 31 ceed the working range of the method and 15 513 19 multiply by the proper dilution factors. 7 811 7.2 To determine micrograms per liter of 9.3 It is estimated that the percent relative suspended recoverable aluminum, subtract dis- standard deviation for total recoverable and solved-aluminum concentration from total- suspended recoverable aluminum and for recoverable-aluminum concentration. recoverable aluminum in bottom material will 7.3 To determine micrograms per gram of be greater than that reported for dissolved aluminum in bottom-material samples, first aluminum. determine the micrograms per liter aluminum 9.4 Precision for total recoverable aluminum in each sample as in paragraph 7.1; then expressed in terms of percent relative standard deviation for two water-suspended sediments is mL of original digest as follows: Aig/L A1X 1,000 Al Number of Relative standard deviation wt of sample (g) laboratories frO/D (percent) 12 4450 13 7 5530 33 8. Report 8.1 Report aluminum, dissolved (01106), References total-recoverable (01105), and suspended- Ramakrishna, T. V., West, P. W., and Robinson, J. W., 1967, recoverable (01107), concentrations as follows: The determination of aluminum and beryllium by less than 10,000 /ig/L, nearest 100 /ig/L; 10,000 atomic absorption spectroscopy: Analytics Chimica /xg/L and above, two significant figures. Acta, v. 39, p. 81-87. Aluminum, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Aluminum, total, 1-5473-85 (mg/kg as Al): none assigned Aluminum, total, 1-5474-85 (mg/kg as Al): none assigned

2. Summary of method method 1-5473, metals, major, total-in-sedi­ 2.1 A sediment is dried, ground, and homog­ ment, atomic absorption spectrometric, direct. enized. The sample is then treated and analyzed 2.1.2 The sample is digested with a combi­ by one of the following techniques. nation of nitric, hydrofluoric, and perchloric 2.1.1 The sample is fused with a mixture of acids in a Teflon beaker, heated on a hotplate lithium metaborate and lithium tetraborate in a at 200 °C. Aluminum is determined on the graphite crucible in a muffle furnace at 1000 °C. resulting solution by atomic absorption spec­ The resulting bead is dissolved in acidified, boil­ trometry. See method 1-5474, metals, major ing, demineralized water, and aluminum is deter­ and minor, total-in-sediment, atomic absorption mined by atomic absorption spectrometry. See spectrometric, direct. 65

Antimony, atomic absorption spectrometric, hydride

Parameters and Codes: Antimony, dissolved, 1-1055-85 (pgtL as Sb): 01095 Antimony, total, I-3055-85 (/ig/L as Sb): 01097 Antimony, suspended total, I-7055-85 (/ig/L as Sb): 01096 Antimony, total-in-bottom material, dry wt, I-5055-85 0*g/g as Sb): 01098

1. Application 3.2 Selenium and arsenic, which also form 1.1 This method may be used to analyze gaseous hydrides, do not interfere at concentra­ water and water-suspended sediment contain­ tions of 100 /ig/L. Greater concentrations were ing at least 1 jig/L of antimony. Samples con­ not tested. taining more than 15 /ig/L need to be diluted. 1.2 Suspended total antimony is calculated by 4. Apparatus subtracting dissolved antimony from total an­ 4.1 Atomic absorption spectrometer and timony. recorder. 1.3 This method may be used to analyze bottom 4.2 Refer to the manufacturer's manual to material containing at least 1 /xg/g of antimony. optimize instrument for the following: Ordinarily, a 100-mg sample of prepared bottom Wavelength —————— 217.6 nm material (method P-0520) is taken for analysis. Source (electrodeless However, if the sample contains more than 15 jxg/g discharge lamp) —— Antimony of antimony, a smaller sample needs to be used. Burner ———————— Three-slot 1.4 Ibtal antimony in water-suspended sedi­ Fuel —————————— Hydrogen ment may be determined after each sample has Diluent ———————— Nitrogen been thoroughly mixed by vigorous shaking and Carrier ———————— Nitrogen a suitable sample portion has been rapidly with­ 4.3 Stibine vapor analyzer (fig. 10) consist­ drawn from the mixture. ing of ___ 4.3.1 Beaker, Berzelius, 200-mL capacity. 2. Summary of method 4.3.2 Gas dispersion tube, coarse frit (Scien­ Organic antimony-containing compounds are tific Glass Apparatus Co. No. JG-8500 has been decomposed by adding sulfuric and nitric acids found satisfactory). and by repeatedly evaporating the sample to 4.3.3 Medicine dropper, 2-mL capacity, min­ fumes of sulfur trioxide. The antimony so liber­ imum, or automatic pipettor, 5-mL capacity. ated, together with inorganic antimony originally present, is subsequently reacted with potas­ 5. Reagents sium iodide and stannous chloride, and finally 5.1 Antimony standard solution /, 1.00 mL= with sodium borohydride to form stibina The 100 fig Sb: Dissolve 0.100 g Sb metal in a min­ stibine is removed from solution by aeration and imum amount of aqua regia. Add demineralized swept by a flow of nitrogen into a hydrogen dif­ water to increase rate of dissolution and dilute fusion flame, where it is determined by atomic to 1000 mL with demineralized water. absorption at 217.6 mn. 5.2 Antimony standard solution II, 1.00 mL=10.0 fig Sb: Dilute 50.0 mL antimony 3. Interferences standard solution I to 500.0 mL with demineral­ 3.1 Since the stibine is freed from the original ized water. sample matrix, interferences in the flame are 5.3 Antimony standard solution III, 1.0 mL— niinirnized. 0.10 fig Sb: Dilute 5.0 mL antimony standard

67 68 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS solution II to 500.0 mL with demineralized concentrated H2SO4 (sp gr 1.84) to 250 mL water. Prepare fresh before each use. demineralized water. 5.4 Hydrochloric acid, concentrated (sp gr 1.19). 6. Procedure 5.5 Nitric acid, concentrated (sp gr 1.41). 6.1 Follow instructions in paragraph 6.1.1 for water or water-suspended sediment and in 5.6 Potassium iodide solution, 15 g/100 mL: paragraph 6.1.2 for bottom material. Dissolve 15 g KI in 100 mL demineralized 6.1.1 Pipet a volume of well-mixed sample con­ water. This solution is stable when stored in an taining less than 1.5 /*g Sb (100 mL max) into amber bottle. a 200-mL Berzelius beaker and dilute to 100 mL 5.7 Sodium borohydride solution, 4 g/100 with demineralized water. mL: Dissolve 4 g NaBH4 and 2 g NaOH in 6.1.2 Weigh a portion of the prepared bottom- 100 mL demineralized water. Prepare fresh material sample containing less than 1.5 fig Sb before each use. (100 mg max); transfer to a 200-mL Berzelius 5.8 Stannous chloride solution, 4.2 g/100 mL beaker and add 100 mL demineralized water concentrated HC1: Dissolve 5 g SnCl2*2H2O in (NOTE 1). 100 mL concentrated HC1 (sp gr 1.19). This solu­ NOTE 1. Do not use more than 100 mg of bot­ tion is unstable. Prepare fresh daily. tom material; otherwise, severe bumping and 5.9 Sulfuric acid, 9M: Cautiously, and with loss of antimony may occur during the subse­ constant stirring and cooling, add 250 mL quent digestion of the sample.

Auxiliary nitrogen Burner

Gas dispersion tube Dropper

utlet tube

Rubber stopper

Hydrogen Nitrogen

200-mL Berzelius beaker or 300-mL fleaker Figure 10.—Stibine vapor analyzer METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 69

6.2 Prepare, in 200-mL Berzelius beakers, a 1,000 blank and sufficient standards containing from Sb (/ig/L)= Sb in sample mL sample 0.1 to 1.5 fig Sb by diluting 1.0 to 15.0 mL por­ tions of antimony standard solution III to 100 mL with demineralized water. 7.3 To determine the concentration of 6.3 To each beaker, add 7 mL 9M H2SO4 suspended total antimony, subtract dissolved- and 5 mL concentrated HNO3. Add a small antimony concentration from total-antimony boiling chip and carefully evaporate to fumes concentration. of SO3. Maintain an excess of HNO3 until all 7.4 Determine the concentration of anti­ organic matter is destroyed. This prevents dark­ mony in air-dried bottom material as follows: ening of the solution and possible reduction and loss of antimony. Cool, add 25 mL demineralized IAg Sb in sample Sb water, and again evaporate to fumes of SO3 to wt of sample (g) expel oxides of nitrogen. 6.4 Cool, and adjust the volume of each beaker to approx 100 mL with demineralized 8. Report water. 8.1 Report antimony, dissolved (01095), 6.5 To each beaker, add successively, with total (01097), and suspended-total (01096), con­ thorough mixing after each addition, 8 mL centrations as follows: less than 100 /ig/L, concentrated HC1, 1 mL KI solution, and 0.5 nearest microgram per liter; 100 jig/L and mL SnCl2 solution. Allow about 15 min for above, two significant figures. reaction to proceed. 8.2 Report antimony, total-in-bottom- 6.6 Attach one beaker at a time to the rub­ material (01098), concentrations as follows: less ber stopper containing the gas dispersion tube. than 100 /ig/g, nearest microgram per gram; 100 6.7 Fill the medicine dropper with 2 mL and above, two significant figures. NaBH4 solution and insert into hole in rubber stopper. 9. Precision 6.8 Add the NaBH4 solution to the sample 9.1 Precision for dissolved antimony for solution. After the absorbance has reached a seven samples expressed in terms of percent maximum and has returned to the baseline, relative standard deviation is as follows: remove the beaker. Rinse the gas dispersion Number of Mean Relative standard deviation tube in demineralized water before proceeding laboratories fafl/l) _____(percent)_____ to the next sample. Treat each succeeding sam­ 3 2.0 0 ple, blank, and standard in a like manner. 3 2.0 50 3 2.3 26 3 4.3 28 7. Calculations 3 4.3 35 7.1 Determine the micrograms of antimony 3 4.7 13 in each sample from a plot of absorbances of 3 8.0 0 standards. Exact reproducibility is not ob­ tained, and an analytical curve must be pre­ 9.2 It is estimated that the percent relative pared with each set of samples. standard deviation for total and suspended 7.2 Determine the concentration of dis­ total antimony and for total antimony in bot­ solved or total antimony in each sample as tom material will be greater than that reported follows: for dissolved antimony.

Antimony, total-in-sediment, atomic absorption spectrometric, hydride

Parameter and Code: Antimony, total, 1-5475-85 (mg/kg as Sb): none assigned

2. Summary of method hotplate at 200 °C. Antimony is determined on A sediment sample is dried, ground, and the resulting solution by atomic absorption homogenized. The sample is digested with a spectrometry. See method 1-5475, metals, combination of nitric, hydrofluoric, and per­ minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a spectrometric, hydride. 71

Arsenic, atomic absorption spectrometric, hydride

Parameters and Codes:3 Arsenic, dissolved, 1-1062-85 (/*g/L as As): 01000 Arsenic, total, I-3062-85 (^g/L as As): 01002 Arsenic, suspended total, I-7062-85 (/xg/L as As): 01001 Arsenic, totat-in-bottom-materiai, dry wt, I-5062-85 (/ig/g as As): 01003

1. Application 3. Interferences 1.1 This method may be used to analyze Since the arsine is freed from the original sam­ water and water-suspended sediment contain­ ple matrix, interferences in the flame are ing at least 1 /ig/L of arsenic. Samples contain­ minimized. ing more than 20 jig/L need to be diluted. 1.2 Suspended total arsenic is calculated by 4. Apparatus subtracting dissolved arsenic from total arsenic. 4.1 Atomic absorption spectrometer and 1.3 This method may be used to analyze bot­ recorder. tom material containing at least 1 jig/g of arsenic. 4.2 Refer to the manufacturer's manual to Ordinarily, a 100-mg sample of prepared bottom optimize instrument for the following: material (method P-0520) is taken for analysis. Grating ———————— Ultraviolet However, if the sample contains more than 10 Wavelength ————— 193.7 nm pg/g of arsenic, a smaller sample needs to be used. Source (electrodeless 1.4 Total arsenic in water-suspended sedi­ discharge ment may be determined after each sample has lamp) ————————— Arsenic been thoroughly mixed by vigorous shaking and Burner ———————— Three-slot a suitable sample portion has been rapidly Fuel —————————— Hydrogen withdrawn from the mixture. Diluent ———————— Nitrogen 1.5 Both inorganic and organic forms of Carrier ———————— Nitrogen arsenic are determined. To determine only in­ 4.3 Arsine vapor analyzer (fig. 11) consisting organic arsenic, omit the strong-acid digestion, paragraphs 6.4 and 6.5 of the procedure. of___ 4.3.1 Beaker, Berzelius, 200-mL capacity, or 2. Summary of method fleaker, 300-mL capacity. Organic arsenic-containing compounds are 4.3.2 Gas dispersion tube, coarse frit (Scien­ decomposed by adding sulfuric and nitric acids tific Glass Apparatus Co. No. JG-8500 has been and repeatedly evaporating the sample to fumes found satisfactory). of sulfur trioxide. The arsenic (V) so liberated, 4.3.3 Medicine dropper, 2-mL capacity, mini­ together with inorganic arsenic originally pre­ mum, or automatic pipettor, 5-mL capacity. sent, is subsequently reduced to arsenic (III) by potassium iodide and stannous chloride, and 5. Reagents finally to gaseous arsine by sodium borohydride 5.1 Arsenic standard solution 7, 1.00 mL= in hydrochloric acid solution. The arsine is 1.00 mg As: Dissolve 1.320 g As2O3, dried for removed from solution by aeration and swept 1 h at 110°C, in 10 mL 10M NaOH and dilute by a flow of nitrogen into a hydrogen diffusion to 1,000 mL with demineralized water. This flame, where it is determined by atomic absorp­ solution is stable. However, it should be pre­ tion at 193.7 nm. pared fresh every 6 months.

73 74 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Arsenic standard solution II, 1.00 mL= 5.7 Sodium borohydride solution, 4 g/100 10.0 jig As: Dilute 5.00 mL arsenic standard mL: Dissolve 4 g NaBH4 and 2 g NaOH in 100 solution I and 1 mL concentrated HNO3 (sp gr mL demineralized water. Prepare fresh before 1.41) to 500.0 mL with demineralized water. each use. Discard after 3 months. 5.8 Stannous chloride solution, 33.6 5.3 Arsenic standard solution III, 1.00 mL= g/lOOmL concentrated HC1: Dissolve 40g 0.10 fig As: Dilute 5.00 mL arsenic standard SnCl2-2H2O in 100 mL concentrated HC1. This solution II and 1 mL concentrated HNO3 (sp gr solution is unstable. Prepare fresh daily. 1.41) to 500.0 mL with demineralized water. 5.9 Sulfuric acid, 9M: Cautiously, and with Prepare fresh weekly. constant stirring and cooling, add 250 mL 5.4 Hydrochloric acid, concentrated (sp gr concentrated H28O4 (sp gr 1.84) to 250 mL 1.19): Use analytical-grade acid with arsenic con­ demineralized water. tent not greater than 1 X 10~6 percent. 5.5 Nitric acid, concentrated (sp gr 1.41): Use 6. Procedure analytical-grade acid with arsenic content not 6.1 Clean all glassware used in this determin­ greater than 5 X 10~7 percent. ation with dilute HC1 (1+4) and rinse with 5.6 Potassium iodide solution, 15 g/100 mL: demineralized water immediately before each usa Dissolve 15 g KI in 100 mL demineralized water. 6.2 Follow instructions in paragraph 6.2.1 for This solution is stable when stored in an amber water or water-suspended sediment and para­ bottle. graph 6.2.2 for bottom material Auxiliary nitrogen Burner

Gas dispersion tube Dropper

tube

Rubber stopper

Hydrogen Nitrogen

200-mL Berzeiius beaker or 300-ml fleaker Figure 11.—Arsine vapor analyzer METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 75 6.2.1 Pipet a volume of well-mixed sample to next sample. Test each succeeding sample, containing less than 1.0 peg As (50 mL max) in­ blank, and standard in a like manner. to a 200-mL Berzelius beaker or 300-mL fleaker and dilute to 50 mL (NOTE 1). 7. Calculations NOTE 1. If fleakers are used, maximum vol­ 7.1 Determine the micrograms of arsenic in ume can be 100 mL. Reagent volumes should the sample from a plot of absorbances of stand­ be doubled. ards. Exact reproducibility is not obtained and 6.2.2 Weigh a portion of prepared bottom- an analytical curve must be prepared with each material sample containing less than 1 /ig of As set of samples. (100 mg max) (NOTE 2); transfer to a 200-mL 7.2 Determine the concentration of dis­ Berzelius beaker or 300-mL fleaker and add 50 solved or total arsenic in each sample as follows: mL demineralized water (NOTE 1). NOTE 2. Do not use more than 100 mg of bot­ tom material to avoid severe bumping and loss 1000 As (/ig/L)=jig As in sample X of arsenic. mL sample 6.3 Prepare, in 200-mL Berzelius beakers or 300-mL fleakers, a blank, and sufficient stand­ 7.3 To determine the concentration of sus­ ards containing from 0.1 to 1.0 /tg As by dilut­ ing 1.0 to 10.0-mL portions of arsenic standard pended total arsenic, subtract dissolved-arsenic concentration from total-arsenic concentration. solution III. Dilute each to approx 50 mL. 7.4 Determine the concentration of arsenic 6.4 To each beaker, add 7 mL 9M H2SO4 in air-dried bottom-material samples as follows: and 5 mL concentrated HNO3. Add a small boiling chip or glass beads and carefully evap­ orate to fumes of SO3. Maintain an excess of jig As in sample As (jig/g)= HNO3 until all organic matter is destroyed. wt of sample (g) This prevents darkening of the solution and possible reduction and loss of arsenic. Cool, add 25 mL demineralized water, and again evapo­ 8. Report rate to fumes of SO3 to expel oxides of nitrogen 8.1 Report arsenic, dissolved (01000), total (NOTE 3). (01002), and suspended-total (01001), concentra­ NOTE 3. If only inorganic arsenic is to be de­ tions as follows: less than 10 /ig/L, nearest termined, omit steps 6.4 and 6.5. microgram per liter; 10 /*g/L and above, two sig­ 6.5 Cool, and adjust each beaker to approx nificant figures. 50 mL with demineralized water. 8.2 Report arsenic, total-in-bottom-material 6.6 To each beaker, add successively, with (01003), concentrations as follows: less than 10 thorough mixing after each addition, 8 mL /xg/g, nearest microgram per gram; 10 pglg and concentrated HC1, 4 mL KI solution, and 1 mL above, two significant figures. SnCl2 solution. Allow about 15 min for reduc­ tion of the arsenic to the tervalent state. 9. Precision 6.7 Attach one beaker at a time to the rub­ 9.1 Precision for dissolved arsenic for 14 ber stopper containing the gas dispersion tube. samples within the range of 1.8 to 43.7 /zg/L 6.8 Fill the medicine dropper with 2 mL may be expressed as follows: NaBH4 solution and insert into the hole in the rubber stopper. Alternatively, the NaBH4 solu­ Sr=0.262X+ 0.346 tion may be delivered from an automatic pipettor. where 6.9 Add the NaBH4 solution to the sample ST= overall precision, micrograms per liter, solution. After the absorbance has reached a and maximum and has returned to the baseline, X= concentration of arsenic, micrograms per remove the beaker. Rinse the gas dispersion liter. tube in demineralized water before proceeding The correlation coefficient is 0.8801. 76 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 9.2 Precision for dissolved arsenic for five of standard deviation for total and suspended the 14 samples expressed in terms of the per­ arsenic and for total arsenic in bottom material cent relative standard deviation is as follows: will be greater than that reported for dissolved arsenic. Number of Mean Relative standard deviation laboratories fcg/L) _____(percent)_____ 9.4 Precision for total arsenic for two water- 5 1.8 61 suspended sediments expressed in terms of the 7 10.9 30 percent relative standard deviation is as follows: 8 19.5 32 6 41.7 18 Number of Mean Relative standard deviation 6 43.7 35 laboratories Qig/L) _____(percent)_____ 6 16 22 9.3 It is estimated that the percent relative 9 6.1 38 Arsenic, atomic absorption spectrometric, hydride, automated

Parameters and Codes: Arsenic, dissolved, 1-2062-85 (^g/L as As): 01000 Arsenic, total, I-4062-85 (^g/L as As): 01002 Arsenic, suspended total, I-7062-85 (pg/L as As): 01001 Arsenic, total-in-bottom-material, dry wt, I-6062-85 (/*g/g as As): 01003

1. Application borohydride. The arsine is stripped from the 1.1 This method may be used to analyze solution with the aid of nitrogen and is then water and water-suspended sediment contain­ decomposed in a tube furnace placed in the ing at least 1 /xg/L of arsenic. Samples contain­ optical path of an atomic absorption spec­ ing more than 20 jig/L need to be diluted. trometer. 1.2 Suspended total arsenic is calculated by 2.2 For additional information on the deter­ subtracting dissolved arsenic from total arsenic. mination of arsenic in water, see Pierce and 1.3 This method may be used to analyze bot­ others (1976), and Fishman and Spencer (1977). tom material containing at least 1 jtg/g of arsenic (NOTE 1). For samples containing more 3. Interferences than 20 /*g/g, use less sediment. 3.1 Since the arsine is freed from the original NOTE 1. Do not use more than 100 mg sedi­ sample matrix, interferences are minimized. ment, because erratic results and large blanks 3.2 A detailed inorganic-interferences study will occur. showed that most trace elements at concentra­ 1.4 Bottom material may be analyzed by tion levels of less than 300 jig/L do not interfere this procedure after it has been prepared as (Pierce and Brown, 1976). directed in method P-0520. 1.5 Total arsenic in water-suspended sedi­ 4. Apparatus ment may be determined after each sample has 4.1 Atomic absorption spectrometer and been thoroughly mixed by vigorous shaking and recorder. a suitable portion has been rapidly withdrawn 4.2 Refer to manufacturer's manual to op­ from the mixture (NOTE 2). timize instrument for the following: NOTE 2. Do not use a sample containing more Grating ———————— Ultraviolet than 1 g/L sediment. Concentrations greater Wavelength ————— 193.7 nm than 1 g/L cause erratic results. Source (electrodeless- 1.6 Both inorganic and organic forms of discharge lamp) —— Arsenic arsenic are determined. To determine only in­ 4.3 Autotransformer, variable: Superior organic arsenic, omit the acid-persulfate diges­ Powerstat type 3 PN 1010 or equivalent. tion or the ultraviolet radiation. 4.4 Pyrometer, portable, 0°C to 1,200°C. Thermolyne Model PM-20700 or equivalent. 2. Summary of method 4.5 Stripping-condensing column, Pyrex, 2.1 Organic arsenic-containing compounds packed with 3- to 5-mm Pyrex beads (fig. 12). are decomposed either by sulfuric acid-potas­ Cooling of the condensing column is not re­ sium persulf ate digestion or by ultraviolet radi­ quired. The nitrogen gas flow rate is adjusted ation. The arsenic so liberated, together with for maximum sensitivity by analyzing a series inorganic arsenic originally present, is sub­ of identical standards. A flow rate of approxi­ sequently reduced to arsine with sodium mately 200 mL/min has been found satisfactory.

77 78 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Arsenic standard solution II, 1.00 mL= 10.0 p,g As: Dilute 5.00 mL arsenic standard solution I and 1 mL concentrated HNO3 (sp gr 1.41) to 500.0 mL with demineralized water. Discard after 3 months. 5.3 Arsenic standard solution III, 1.00 mL= 0.10 fig As: Dilute 5.00 mL arsenic standard solution II and 1 mL concentrated HNO3 to 500.0 mL with demineralized water. Prepare fresh weekly. 5.4 Arsenic working standards: Prepare daily a blank and 100 mL each of a series of arsenic working standards containing 0.15 mL concentrated HNO3 by appropriate dilution of arsenic standard solution III.

Arsenic standard Arsenic Waste solution III concentration

5. Reagents 6. Procedure 5.1 Arsenic standard solution I, 1.00 mL= 6.1 Set up manifold-acid persulfate (fig. 13) 1.00 mg As: Dissolve 1.320 g As2O3, dried for or ultraviolet radiation (fig. 14). See NOTE 2. 1 h at 110°C, in 10 mL 10M NaOH and dilute 6.2 Apply a voltage of 47 volts or more (vari­ to 1,000 mL with demineralized water. This able autotransformer) as necessary to the tube solution is stable. However, it should be furnace to maintain a constant temperature of prepared fresh every 6 months. 800 °C. Monitor the tube-furnace temperature METHODS FOB DETERMINATION OF INORGANIC SUBSTANCES 79

1(eating bath 40- foot coil O.OSGin Air 10- 1.20 mL/min ti irn co il Sample v —— 088080 — (fflKHTl O.llOin - O 22-turn coil ' i t 3.90 mL/min © Sampler Sulfuric acid 0.035 in 30/h Cooling coil 0.42 mL/min Potassium 1/2 can 114-0209-01 0.073in persulfate 2.00 mL/min Sodium 0.035in hydroxide 0.42 mL/min Potassium 0.035in iodide 0.42 mL/min Sodium 10-turn coil O.llOin borohydride 3.90 mL/min Hydrochloric 20-turn coil O.llOin acid 3.90 mL/min 20-turn coil To sa mpler 4 O.llOin Water 40- foot X^ wash 3.90 mL/min >,time delay coil rec i————— ^ eptacle To separator v,—s- Proportioning pump Figure 13.—Arsenic, acid-persulfate manifold using portable pyrometer with the thermo­ 6.4 Feed all reagents through the system, couple placed in the middle of the tube. using demineralized water in the sample line. 6.3 If bottom-material samples are being Allow the heating bath to warm to 95 °C. analyzed, weigh 100 mg or less of bottom- 6.5 Beginning with the most concentrated material sample (2.0 jig As max), transfer to a standard (NOTE 6), place a complete set of 100-mL volumetric flask, and dilute to volume standards in the first positions of the first sam­ with demineralized water. Sample as directed ple tray. Place individual standards of differing for water and water-suspended sediment sam­ concentrations in every eighth position of the ples in paragraph 6.5 (NOTE 5). remainder of this and subsequent trays. Fill re­ NOTE 5. Bottom material may be manually digested using method 1-5062 (arsenic, atomic mainder of each sample tray with unknown absorption spectrometric) if standards and samples (well mixed). blank are treated identically. Adjust pH of NOTE 6. It is best to place two or three sam­ digested solutions to between 2 and 3 before ples of the most concentrated standard at the proceeding to paragraph 6.5. beginning, since the first peak is usually low. 80 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Proportioning pump

turn coil H""^ O.llOin Sample f ^\ 3.90 mL/min Ultraviolet digestor 0.056in Ai r ———— 1.20 mL/min OdlllplVI 4 Potassium 30/h O.OSSin iodide I/?™™ 0.42 mL/min Sodium O.llOin borohydride 3.90 mL/min Hydrochloric O.llOin acid To 3.90 mL/min 40 -foot Sanipler 4 O.llOin Water •L\time delay coil 3.90 mL/min ) > rec eptacle / Tn senaratnr

Figure 14.—Arsenic, ultraviolet radiation manifold

The first standard should not be used in any of water, begin grinding cell with a steady move­ the calculations. ment from inside to outside of cell. Grind one- 6.6 Remove the sample line from the demin- half of cell at a time and regrind if necessary eralized-water wash solution when the baseline to achieve an even frosting. stabilizes and begin the analyses (NOTE 7). NOTE 7. When the analyses are complete, the 7. Calculations tubes in the manifold and the separator-con- 7.1 Prepare an analytical curve by plotting densor column should be cleaned if any sedi­ the height of each standard peak versus its ment is present. respective arsenic concentration. 6.7 With 10 mV recorder, 20 /ig/L of arsenic 7.2 Determine the concentration of dis­ will give a peak approximately 60 percent of full solved or total arsenic in each sample by com* scale. If the sensitivity drops by 30 percent or paring its peak height to the analytical curve. more, replace or treat the cell by one of the Any baseline drift that may occur must be following methods: taken into account when computing the height 6.7.1 Soak the tube furnace for 30 min in 1:1 of a sample or standard peak. water-hydrofluoric acid solution and rinse with 7.3 To determine the concentration of sus­ demineralized water. pended total arsenic, subtract dissolved-arsenic 6.7.2 Grind the cell with silicon carbide as concentration from total-arsenic concentration. follows: Mount cell with suitable cushioning in 7.4 To determine the concentration of a 3/4-in. chuck on a slowly revolving shaft. Wet arsenic in bottom-material samples, first deter­ inside of cell and apply grinding compound such mine the micrograms per liter of arsenic in each as commercial auto-valve-grinding compound. sample as in paragraph 7.2, then Using a standard speed drill and an aluminum As X 0.1 oxide-grinding wheel suitably reduced in diam­ As (A*g/g)= eter to give adequate clearance, and plenty of wt of sample (g) METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 81

8. Report Mean Relative standard deviation 8.1 Report arsenic, dissolved (01000), total _____(percent)_____ (01002), and suspended-total (01001), concentra­ 5.0 10 tions as follows: less than 10 jig/L, nearest 10.4 10 microgram per liter; 10 /ig/L and above, two sig­ 13.8 4 nificant figures. 8.2 Report arsenic, total-in-bottom-material 9.3 It is estimated that the percent relative (01003), concentrations as follows: less than 10 standard deviation for total and suspended jig/g. nearest microgram per gram; 10 pig/g and arsenic and for arsenic in bottom material will above, two significant figures. be greater than that reported for dissolved arsenic. 9. Precision 9.1 Acid-persulfate digestion: Precision, for dissolved arsenic for replicate analysis by one References operator expressed in terms of percent relative standard deviation, is as follows: Fishman, M. J., Spencer, R. R., 1977, Automated atomic absorption spectrometric determination of total arsenic Relative standard deviation in water and streambed materials: Analytical Chem­ _____(percent)_____ istry, v. 49, p. 1599-1602. Pierce, F. D., Lamoreaux, T. C., Brown, H. R., and Fraser, 5 5 R. S., 1976, An automated technique for the sub-micro- 5 gram determination of selenium and arsenic in surface waters by atomic absorption spectroscopy: Applied 9.2 Ultraviolet radiation: Precision for dis­ Spectroscopy, v. 30, p. 38-42. Pierce, F. D., and Brown, H. R., 1976, Inorganic interference solved arsenic for replicate analysis by one study of automated arsenic and selenium determination operator expressed in terms of percent relative with atomic absorption spectrometry: Analytical standard deviation is as follows: Chemistry, v. 48, p. 693-695.

Arsenic, colorimetric, silver diethyldithiocarbamate

Parameters and Codes: Arsenic, dissolved, 1-1060-85 (^g/L as As): 01000 Arsenic, total, I-3060-85 (/tg/L as As): 01002 Arsenic, suspended total, I-7060-85 (jig/L as As): 01001 Arsenic, total-in-bottom-material, dry wt, I -5060 -85 (/tg/g as As): 01003

1. Application glass wool impregnated with lead acetate so­ 1.1 This method may be used to analyze lution, and into a gas absorber containing water and water-suspended sediment contain­ silver diethyldithiocarbamate (AgDDC) dis­ ing from 5 to 200 /ig/L of arsenic. Samples solved in pyridine. Arsine reacts with AgDDC containing more than 200 /xg/L need to be to form a soluble red complex having maxi­ diluted. mum absorbance at about 535 nm. The absor- 1.2 Suspended total arsenic is calculated by bance of the solution is measured spectro- subtracting dissolved arsenic from total arsenic. photometrically, and arsenic determined by 1.3 This method may be used to analyze bot­ reference to an analytical curve prepared from tom material containing from 5 to 200 /ig/g of standards. arsenic. Usually, a 100-mg sample of prepared 2.2 Additional information on the determin­ bottom material (method P-0520) is taken for ation is given by Liederman and others (1959); analysis. If the sample contains more than 200 by Ballinger and others (1962); by Stratton and Mg/g °f arsenic, a smaller sample needs to be Whitehead (1962); and by Fresenius and used. Schneider (1964). 1.4 Total arsenic in water-suspended sedi­ ment may be determined after each sample has 3. Interferences been thoroughly mixed by vigorous shaking and 3.1 Some samples may contain sulfides; a suitable sample portion has been rapidly however, small quantities are effectively re­ withdrawn from the mixture. moved by a lead acetate scrubber. Several 1.5 Both inorganic and organic forms of metals—cobalt, nickel, mercury, silver, plati­ arsenic are determined. To determine only in­ num, copper, chromium, and molybdenum- organic arsenic, omit the strong-acid digestion, interfere with the evolution of arsine. Antimony paragraphs 6.4 and 6.5 of the procedure. salts, under the reducing conditions in the generator, form stibine, which passes into the 2. Summary of method absorber and causes high results. 2.1 Organic compounds are decomposed by 3.2 The blank and standards fade slowly on adding sulfuric and nitric acids, and by repeat­ standing, but not enough to influence results edly evaporating the samples to fumes of sulfur significantly during the first 20 min. trioxide. The arsenic (V) so liberated, together with inorganic arsenic originally present, is sub­ 4. Apparatus sequently reduced to arsenic (III) by potassium 4.1 Arsine generator, scrubber, and absorber iodide and stannous chloride, and finally to (fig. 15). gaseous arsine by zinc in hydrochloric acid solu­ 4.2 Spectrophotometer, for use at 535 nm. tion. The resultant mixture of gases is passed 4.3 Refer to the manufacturer's manual to through a scrubber consisting of borosilicate optimize instrument.

83 84 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS solution II and 1 mL concentrated HNO3 (sp gr 1.41) to 100.0 mL with demineralized water. Prepare fresh weekly. 5.4 Hydrochloric acid, concentrated (sp gr 1.19): Use analytical-grade acid with arsenic content not greater than 1X10"6 percent. 5.5 Lead acetate solution, 8.6 g/100 mL: Dissolve 10 g (CH3COO)2Pb-3H2O in 100 mL demineralized water. Keep tightly stoppered. 5.6 Nitric acid, concentrated (sp gr 1.41): Use analytical-grade acid with arsenic content not greater than 5X10~7 percent. 5.7 Potassium iodide solution, 15 g/100 mL: Dissolve 15 g KI in 100 mL demineralized water. This solution is stable when stored in an amber bottle. 5.8 Silver diethyldithiocarbamate (AgDDC) solution, 0.5 g/100 mL: Dissolve 1 g (C2H5)2 NCSSAg in 200 mL pyridine. This solution is stable when stored in an amber bottle. 5.9 Stannous chloride solution, 33.6 g/100 mL concentrated HC1: Dissolve 40 g arsenic-free SnCl2-2H2O in 100 mL concentrated HCL This solution is unstable. Prepare fresh daily. 5.10 Sulfuric acid, 9M: Cautiously, and with constant stirring and cooling, add 250 mL concentrated H2SO4 (sp gr 1.84) to 250 mL demineralized water. 5.11 Zinc: Granular zinc, about 20 mesh, with arsenic content not greater than 1X10"6 percent.

6. Procedure 6.1 Clean all glassware used in this deter­ Figure 15.—Arsine generator, scrubber, and absorber mination with warm, dilute HNO3 (1+4) and rinse with demineralized water immediately before each use. The absorbers must also be 5. Reagents rinsed with acetone and air-dried or briefly 5.1 Arsenic standard solution I, 1.00 mL= oven-dried. 1.00 mg As: Dissolve 1.320 g As2O3, dried for 6.2 Follow instructions in paragraph 6.2.1 1 h at 110°C, in 10 mL 10M NaOH and dilute for water or water-suspended sediment and in to ltOOO mL with demineralized water. This paragraph 6.2.2 for bottom material. solution is stable. However, it should be pre­ 6.2.1 Pipet a volume of well-mixed sample pared fresh every 6 months. containing less than 20 /tg As (100 mL max) into 5.2 Arsenic standard solution II, 1.00 mL= the flask of an arsine generator. Rinse the pipet 10.0 /ig As: Dilute 5.00 mL arsenic standard with demineralized water to remove adhering solution I and 1 mL concentrated HNO3 (sp gr particles and combine with the sample. Dilute 1.41) to 500.0 mL with demineralized water. the sample to approx 100 mL if less than 100 Discard after 3 months. mL is used. 5.3 Arsenic standard solution HI, 1.00 mL= 6.2.2 Weigh a portion (NOTE 1) of prepared 1.00 fig As: Dilute 10.0 mL arsenic standard bottom-material sample (method P-0520) METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 85 containing less than 20 fig As and transfer to 7.2 Determine the concentration of dis­ the flask of an arsine generator. Add approx 100 solved or total arsenic in each sample as follows: mL demineralized water. NOTE 1. The sample weight must not exceed 1000 100 mg; otherwise severe bumping and loss of As (jig/L)= X/ig As in sample arsenic may occur. mL sample 6.3 Prepare a blank and sufficient standards (20 pg As max), and adjust the volume of each 7.3 To determine the concentration of to approx 100 mL with demineralized water. suspended total arsenic, subtract dissolved- 6.4 To each flask, add 7 mL 9M H2SO4 and arsenic concentration from total-arsenic 5 mL concentrated HNO3. Add a small boiling concentration. chip and carefully evaporate to fumes of SO3. 7.4 Determine the concentration of arsenic Cool, add 25 mL demineralized water, and again in bottom-material samples as follows: evaporate to fumes of SO3 to expel oxides of nitrogen. Maintain excess of HNO3 until all fig As per sample As (/ig/g)= organic matter is destroyed. This prevents wt of sample (g) darkening of the solution and possible reduction and loss of arsenic. 8. Report 6.5 Cool, and adjust the volume to approx 8.1 Report arsenic, dissolved (01000), total 100 mL. (NOTE 2). (01002), and suspended-total (01001), concentra­ NOTE 2. If only inorganic arsenic is to be de­ tions as follows: less than 10 pg/L, nearest termined, omit steps 6.4 and 6.5* microgram per liter; 10 jig/L and above, two sig­ 6.6 To each flask add successively, with nificant figures. thorough mixing after each addition, 10 mL 8.2 Report arsenic, total-in-bottom-material concentrated HC1,4 mL KI solution, and 1 mL (01003), concentrations as follows: less than 100 SnCl2 solution. Allow about 15 min for reduc­ Mg/g» to the nearest 10 /ig/g; 100 jtg/g and above, tion of the arsenic to the tervalent state. two significant figures. 6.7 Place in each scrubber a plug of boro- silicate glass wool that has been impregnated 9. Precision with lead acetate solution. Assemble the gen­ 9.1 Precision for dissolved arsenic for 22 erator, scrubber, and absorber, making certain samples within the range of 2.7 to 109 jig/L may that all parts fit and are correctly adjusted. be expressed as follows: Add 3.00 mL silver diethyldithiocarbamate- pyridine solution to each absorber. Add glass Sr= 0.225X + 2.426 beads to the absorbers until the liquid just covers them. where 6.8 Disconnect each generator, add 6 g gran­ ST= overall precision, micrograms per liter, ular zinc, and reconnect immediately. and 6.9 Allow 30 min for complete evolution of X= concentration of arsenic, micrograms per the arsine. Warm the generator flasks for a few liter. minutes to make sure that all the arsine is The correlation coefficient is 0.9430. released, and then pour the solutions from the 9.2 Precision for dissolved arsenic for five of absorbers directly into the spectrophotometer's the 22 samples expressed in terms of the per­ cells. Determine the absorbances of the stand­ cent relative standard deviation is as follows: ards and samples against the blank without un­ necessary delay, as the color developed is not Number of Mean Relative standard deviation permanent. laboratories _____(percent) _____ 3 2.7 85 7. Calculations 12 9.8 42 7 21.0 26 7.1 Determine the micrograms arsenic in the 10 40.0 40 sample from a plot of absorbances of standards. 16 109 24 86 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 9.3 It is estimated that the percent relative Fresenius, W., and Schneider, W., 1964, Determination of standard deviation for total and suspended slight amounts of arsenic with silver diethyldithiocar­ bamate in water analysis: Journal of Analytical arsenic and for total arsenic in bottom material Chemistry, v. 203, p. 417-422. will be greater than that reported for dissolved Liederman, D., Bowen, J. E., and Milner, O. I., 1959, arsenic. Determination of arsenic in petroleum stocks and catalysts by evolution of arsine: Analytical Chemistry, References v. 31, p. 2052-5. Bafflnger, D. G., Lishka, R. J., and Gales, M. E., 1962, Stratton, G., and Whitehead, H. E., 1962, Colorimetric Application of the silver diethyldithiocarbamate method determination of arsenic in water with silver diethyl­ to the determination of arsenic: American Water Works dithiocarbamate: American Water Works Association Association Journal, v. 54, p. 1424-1428. Journal, v. 54, p. 861-4. Arsenic, total-in-sediment, atomic absorption spectrometric, hydride

Parameter and Code: Arsenic, total, 1-5475-85 (mg/kg as As): none assigned

2. Summary of method hotplate at 200 °C. Arsenic is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec- homogenized. The sample is digested with a trometry. See method 1-5475, metals, minor, combination of nitric, hydrofluoric, and per­ total-in-sediment, atomic absorption spec­ chloric acids in a Teflon beaker heated on a trometric, hydride.

87

Barium, atomic absorption spectrometric, direct

Parameters and Codes: Barium, dissolved, 1-1084-85 (jig/l as Ba): 01005 Barium, total recoverable, I -308 4 -85 fcg/L as Ba): 01007 Barium, suspended recoverable, I-7084-85 (pg/L as Ba): 01006 Barium, recoverable-from-bottom-material, dry wt, 1-5084-85 fcig/g as Ba): 01008

1. Application 4.2 Refer to the manufacturer's manual to 1.1 This method may be used to analyze optimize instrument for the following: water and water-suspended sediment contain­ Grating ———————— Visible ing at least 100 ptg/L of barium. Sample solu­ Wavelength ————— 553.6 nm tions containing more than 5000 /ig/L need to Source (hollow-cathode be diluted. lamp) ———————— Barium 1.2 Suspended recoverable barium is calcu­ Burner ———————— Nitrous oxide lated by subtracting dissolved barium from Oxidant ———————— Nitrous oxide total-recoverable barium. Fuel —————————— Acetylene 1.3 This method may be used to analyze bot­ Type of flame ———— Fuel-rich tom material containing at least 5 uglg of barium. 5. Reagents 1.4 Tbtal recoverable barium in water- 5.1 Barium standard solution, 1.00 mL= suspended sediment needs to undergo prelim­ 100 us Ba: Dissolve 0.1516 g BaCl2-2H2O, dried inary digestion-solubilization by method at 180 °C for 1 ht in demineralized water and 1-3485, and recoverable barium in bottom dilute to 1,000 mL. material needs to undergo preliminary diges­ 5.2 Barium working standards: Prepare a tion-solubilization by method 1-5485 before be­ series of at least six working standards con­ ing determined. taining from 100 to 5,000 jig/L of barium by appropriate dilution of barium standard so­ 2. Summary of method lution. Add 1.00 mL NaCl solution for each Barium is determined by atomic absorption 10 mL of working standard. Similarly prepare spectrometry. Sodium chloride is added to con­ a demineralized water blank. Prepare fresh trol ionization of barium in the flama daily. 5.3 Sodium chloride solution, 25.4 g/L: 3. Interferences Dissolve 25.4 g NaCl in demineralized water and The use of a nitrous oxide-acetylene flame vir­ dilute to 1 L. tually eliminates chemical interferences in the determination of barium. However, barium is 6. Procedure easily ionized in the nitrous oxide-acetylene 6.1 Add 1.0 mL NaCl solution to 10.0 mL flame; to control this effect, sodium chloride solu­ sample solution and mix thoroughly. tion must be added to each sample and standard. 6.2 Aspirate the blank to set the automatic zero control. Use the automatic concentration 4. Apparatus control to set the concentrations of standards. 4.1 Atomic absorption spectrometer Use at least six standards. Calibrate the instru­ equipped with electronic digital readout and ment each time a set of samples is analyzed and automatic zero and concentration controls. check calibration at reasonable intervals. 89 90 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 7. Calculations 9. Precision 7.1 Determine the micrograms per liter of 9.1 The standard deviation for dissolved dissolved or total recoverable barium in each barium within the range of 43 to 800 jig/L for sample from the digital display or printer while 17 samples was found to be independent of aspirating each sample. Dilute those samples concentration. The 95-percent confidence inter­ containing concentrations of barium that ex­ val for the average standard deviation of 93.5 ceed the working range of the method and jig/L ranged from 85.3 to 103.2 jig/L. multiply by the proper dilution factors. 9.2 Precision for dissolved barium for five of 7.2 To determine micrograms per liter of the 17 samples expressed in terms of the per­ suspended recoverable barium, subtract dis- cent relative standard deviation is as follows: solved-barium concentration from total-recover­ able-barium concentration. Number of Relative standard deviation 7.3 To determine micrograms per gram of laboratories WU _____(percent)_____ barium in bottom-material samples, first deter­ 13 43 70 mine the micrograms per liter of barium in each 17 112 53 18 294 32 sample as in paragraph 7.1, then: 9 756 7 6 800 0 mL of original digest /ig/L BaX 1,000 ~ 9.3 It is estimated that the percent relative Ba standard deviation for total recoverable and wt of sample (g) suspended recoverable barium and for recover­ able barium in bottom material will be greater 8. Report than that reported for dissolved barium. 8.1 Report barium, dissolved (01005), total- 9.4 Precision expressed in terms of percent recoverable (01007), and suspended-recoverable relative standard deviation for total recoverable (01006), concentrations as follows: less than barium for two water-suspended sediments is 1,000 /ig/L, nearest 100 j*g/L; 1,000 pg/L and as follows: above, two significant figures. 8.2 Report barium, recoverable-from- Number of Relative standard deviation bottom-material (01008), concentration as laboratories _____(percent)______follows: less than 100 pglg, nearest 10 pglg; 100 12 91.7 86 /xg/g and above, two significant figures. 10 172 40 Barium, atomic emission spectrometric, ICP

Parameter and Code: Barium, dissolved, 1-1472-85 faglL as Ba): 01005

2. Summary of method method utilizing an induction-coupled argon Barium is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 91

Beryllium, atomic absorption spectrometric, direct

Parameters and Codes: Beryllium, dissolved, 1-1095-85 fcig/L as Be): 01010 Beryllium, total recoverable, I-3095-85 (jig/L as Be): 01012 Beryllium, suspended recoverable, I-7095-85 fcg/L as Be): 01011 Beryllium, recoverable-from-bottom-material, dry wt, I-5095-85 (pg/g as Be): 01013

1* Application 3.4 Sodium and silicon at concentrations in 1.1 This method may be used to analyze wa­ excess of 1000 mg/L have been reported to ter and water-suspended sediment containing at severely depress the beryllium absorbance least 10 pig/L of beryllium. Sample solutions con­ (Environmental Protection Agency, 1979). taining more than 200 jig/L need to be diluted. 1.2 Suspended recoverable beryllium is 4. Apparatus calculated by subtracting dissolved beryllium 4.1 Atomic absorption spectrometer from total recoverable beryllium. equipped with electronic digital readout and 1.3 This method may be used to analyze bot­ automatic zero and concentration controls. tom material containing at least 0.5 /ig/g of 4.2 Refer to the manufacturer's manual to beryllium. optimize instrument for the following: 1.4 Total recoverable beryllium in water- Grating ——————— Ultraviolet suspended sediment needs to undergo prelim­ Wavelength —————— 234.9 nm inary digestion-solubilization by method Source (hollow-cathode 1-3485, and recoverable beryllium in bottom lamp) ———————— Beryllium material needs to undergo preliminary diges­ Burner ——————— Nitrous oxide tion-solubilization by method 1-5485 before be­ Oxidant ——————— Nitrous oxide ing determined. Fuel ————————— Acetylene Type of flame ———— Fuel-rich 2. Summary of method Beryllium is determined by atomic absorption 5. Reagents spectrometry. Calcium chloride is added to con­ CAUTION: Beryllium compounds and samples trol ionization of beryllium in the flame. with high concentrations of beryllium should be handled with care; they may be carcinogenic. 3. Interferences 5.1 Beryllium standard solution /, 1.00 mL= 3.1 Beryllium is slightly ionized in the ni­ 100 fig Be: Dissolve 0.1000 g Be flakes in a min­ trous oxide-acetylene flame; to control this ef­ imum of aqua regia. Heat to increase rate of fect, calcium chloride solution must be added dissolution. Add 10.0 mL of concentrated to each standard and sample. HNO3 (sp gr 1.41) and dilute to 1000 mL with 3.2 Bicarbonate ion interferes; however, this demineralized water. interference is of no consequence if samples pre­ 5.2 Beryllium standard solution II, 1.00 served by the addition of acid are used for the mL=10.0 /ig Be: Dilute 100.0 mL beryllium analysis. standard solution I to 1,000 mL with demineral­ 3.3 Aluminum at concentrations greater ized water. than 500 j*g/L has been reported to depress the 5.3 Beryllium working standards: Prepare beryllium absorbanca a series of at least six working standards 93 94 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS containing from 10 to 200 /*g/L beryllium by recoverable (01011), concentrations as follows: appropriate dilution of beryllium standard solu­ less than 1,000 pig/L to the nearest 10 Mg/L. tion II. Add 1.0 mL CaCl2 solution for each 10.0 8.2 Report beryllium, recoverable-from- mL of working standard. Similarly prepare a bottom-material (01013), as follows: less than 10 demineralized water blank. Prepare fresh daily. jig/g, nearest microgram per gram; 10 pglg and 5.4 Calcium chloride solution, 27.8 g/L: Sus­ above, two significant figures. pend 25 g CaCO3 in demineralized water and dissolve with a minimun of dilute HC1. Dilute 9. Precision to 1 L with demineralized water. 9.1 The standard deviation for dissolved beryllium within the range of 5.4 to 70 jig/L for 6. Procedure 17 samples was found to be independent of 6.1 Add 1.0 mL CaCl2 solution to 10.0 mL concentration. The 95-percent confidence inter­ sample solution and mix thoroughly. val for the average standard deviation of 4.11 6.2 Aspirate the blank to set the automatic /ig/L ranged from 3.6 to 4.9 jig/L. zero control. Use the automatic concentration 9.2 Precision for dissolved beryllium for four control to set the concentrations of standards. of the 17 samples expressed in terms of the Use at least six standards. Calibrate the instru­ percent relative standard deviation is as ment each time a set of samples is analyzed and follows: check calibration at reasonable intervals. Number of Mean Relative standard deviation laboratories frO/D _____(percent)_____ 7. Calculations 8 5.4 54 7.1 Determine the micrograms per liter of 8 20.8 19 dissolved or total recoverable beryllium in each 11 47.7 9 sample from the digital display or printer while 3 70.0 0 aspirating each sample. Dilute those samples 9.3 It is estimated that the percent relative containing concentrations of beryllium that ex­ standard deviation for total-recoverable and ceed the working range of the method and suspended recoverable beryllium and for recov­ multiply by the proper dilution factors. erable beryllium in bottom material will be 7.2 To determine micrograms per liter of greater than that reported for dissolved suspended recoverable beryllium, subtract dis- beryllium. solved-beryllium concentration from total- 9.4 Precision for total recoverable beryllium recoverable-beryllium concentration. expressed in terms of percent relative standard 7.3 To determine micrograms per gram of deviation for two water-suspended sediments is beryllium in bottom-material samples, first as follows: determine the micrograms per liter of beryllium in each sample as in paragraph 7.1, then: Number of Mean Relative standard deviation laboratories _____ (percent)_____ 4 22.5 27 mL of original digest 64.2 7 /ig/L BeX 5 1,000____ Be (Mg/g)= wt of sample (g) Reference

8. Report U.S. Environmental Protection Agency, 1979, Methods for 8.1 Report beryllium, dissolved (01010), chemical analysis of water and wastes, Cincinnati, total-recoverable (01012), and suspended- p. 210.1-1. Beryllium, atomic emission spectrometric, ICP

Parameter and Code: Beryllium, dissolved, 1-1472-85 (/*g/L as Be): 01010

2. Summary of method method utilizing an induction-coupled argon Beryllium is determined simultaneously plasma as an excitation source. See method with several other constituents on a single sam­ 1-1472, metals, atomic emission spectrometric, ple by a direct-reading emission spectrometric ICP. 95

Boron, atomic emission spectrometric, d-c plasma

Parameter and Code: Boron, dissolved, 1-1114-85 (ftg/L as B): 01020

1. Application Plasma viewing posi­ This method may be used to analyze finished tion ———————— -1 (fig. 16) water, natural water, and industrial water con­ Gas —————————— Argon taining from 10 to 1000 /xg/L of boron. Samples Sleeve pressure ——— 50 psi containing more than 1000 jig/L boron and/or Nebulizer pressure — 25 psi with specific conductances greater than 10,000 Entrance slit ———— 25X300 Mm fiS/cm need to be diluted. Exit slit ——————— 50X300 jun Voltage ——————— 1000 V 2. Summary of method Wavelength ————— 249.773 nm Boron is determined by a direct-reading emis­ Signal amplification - 40- to sion spectrometer that utilizes a d-c argon 60-percent plasma as an excitation source (Johnson and full-scale others, 1979a, b, 1980). A mixture of lithium (1000 chloride, sulfuric acid, and glycerin is added to samples and standards to provide a common 5. Reagents background matrix and to compensate for 5.1 Boron standard solution I, 1.00 mL=100 viscosity changes. The liquid mixture is then jig B: Dissolve 0.5720 g high-purity H3BO3> converted by a ceramic nebulizer into a fine dried over desiccant for 24 h, in demineralized aerosol and introduced into the plasma via a water and dilute to 1000 mL. Store in plastic plastic spray chamber and Pyrex injection tube. bottle. Boron is determined on the basis of the average 5.2 Boron standard solution II, 1.00 of two replicate exposures, each of which is per­ mL=l(KO pig B: Dilute 100,0 mL boron stand* formed on a 10 second integrated intensity. ard solution I to 1000 mL with demineralized Calibration is performed by standardization water. Store in plastic bottle. with a high- standard solution and a blank. 5.3 Boron working standard, 1.00 mL=1.00 pg B: Dilute 100.0 mL boron standard solution 3. Interferences II to 1000 ™T, with demineralized water. Store Stray-light effects in a high-resolution, single- in plastic bottle. element, d-c argon plasma emission spectrom­ 5.4 Glycerin, USP. eter are found to be negligible. 5.5 Lithium chloride, LiCl, reagent-grade. 5.6 Matrix modifier. Dissolve 367 g LiCl in 4. Apparatus 1000 mL demineralized water. Transfer to a 4.1 Spectrometer, Spectrometrics, Spectro- Teflon beaker and add, with stirring, 10.0 mL span IV with d-c argon plasma or equivalent, concentrated H2SO4. Heat the solution to 75 to with Echelle optics, printer, autosampler, and 80°C on a hotplate (asbestos padded) and slowly peristaltic pump. add 25 mL methyl alcohol. Stir rapidly for one 4*2 Refer to manufacturer's manual to op­ hour to volatilize of excess methyl alcohol and timize instrument for the following: any trimethyl borate that forms. Repeat the 97 98 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Excitation NOTE 1. Because of thermal instability in­ region herent with the high-resolution spectrometer, repeak the analytical line if the boron standard drifts more than 3 percent.

7. Calculations The computer system is designed so that the blank and the 1000 /*g/L of boron working Plasma standard are used to establish a two-point calibration curve. The system will convert in­ strument-intensity readings to analytical con­ Figure 16.—Plasma position on entrance slit for ooron centrations. The printer display includes the blank and working-standard instrument intens­ ity readings, blank and standard concentra­ process two more times. Allow the solution to tions, sample instrument intensity readings, cool, transfer to a 4-L polyethylene container, sample concentrations, average of sample and add with stirring 2000 mL glycerin. In a concentrations, and standard deviation. Teflon beaker slowly add, with stirring, 400 mL concentrated H2SO4 to 400 mL demineralized 8. Report water. With stirring and cooling, add 50 mL Report boron, dissolved (01020), concentra­ methyl alcohol. The heat generated should be tions as follows: less than 100 j*g/L, nearest 10 sufficient to volatilize excess methyl alcohol and /ig/L; 100 jig/L and above, two significant any trimethyl borate. When the acid has figures. reached room temperature, add the acid slowly, with stirring (in a hood), to the glycerin-LiCl 9. Precision mixture. Dilute to 4,000 mL with demineralized Precision based on 12 determinations by a water. single operator expressed in terms of standard 5.7 Methyl alcohol, reagent-grade. deviation and percent relative standard devi­ 5.8 Sulfuric acid, concentrated (sp gr 1.84), ation is as follows: Ultrex or equivalent.

Mean Standard deviation Relative standard deviation 6. Procedure (percent) 6.1 Pipet 10.0 mL sample into a disposable 30.8 1.8 5.8 plastic test tube. 40.8 1.8 4.4 6.2 Pipet 100 mL demineralized-water blank 215 5.0 2.3 425 1.3 0.3 and working standard into plastic bottles. 6.3 Add 2.0 mL matrix modifier to the sam­ ple and 20.0 mL to the blank and working References standard. 6.4 Place plastic caps on the tube and bot­ Johnson, G. W., Taylor, H. E., and Skogerboe, B. K, 1979a, tles and mix well. Determination of trace elements in natural waters by 6.5 Refer to manufacturer's manual for com­ the D.C. Argon-plasma, multielement atomic emission spectrometer (DCP-MAES) technique: Spectrochimica puter-operating procedure. Use the prepared Acta, v. 34B, p. 197-212. blank and working standard for instrument ___1979b, Evaluation of spectral interferences associated calibration and all subsequent recalibrations. with a direct current plasma-multielement atomic emis­ 6.6 Refer to manufacturer's manual for auto- sion spectrometer {DCP-MAES) system: Applied Spec- sampler-operating procedures. Pour samples in troscopy, v. 33, p. 451-456. ___1980, Characterization of an interelement enhance­ autosampler tray, positioning a blank and work­ ment effect in a dc plasma atomic emission spec- ing standard after every five samples for recali- trometry system: Applied Spectroscopy, v. 34, bration. Begin analysis (NOTE 1). p. 19-24. Boron, colorimetric, azomethine H, automated-segmented flow

Parameter and Code: Boron, dissolved 1-2115-85 (/*g/L as B): 01020

1. Application 300 g NH4C2H3O2 in 1,000 mL of demineral- This method may be used to determine con­ ized water. Adjust the pH to 6.35 with 6N sul- centrations of boron in unacidified water in the furic acid and filter. range of 10 to 400 /ig/L. Sample solutions con­ 5.2 Azomethine H synthesis: Dissolve 18 g taining more than 400 /ig/L boron need to be H-acid (8-amino-l-naphthol-3,6-disulphonic diluted. acid) in 1,000 mL of demineralized water with gentle heating. Filter, with suction, through 2. Summary of method Whatman No. 40 filter paper. Neutralize the The condensation product of H-acid (8-amino- solution to pH 7 with 2M KOH. While stirring l-napthol-3,6-disulphonic acid) and salicylalde- continuously, add concentrated HC1 (sp gr 1.19) hyde is azomethine H, which forms a yellow until the pH is about 1.5. To the resulting mix­ complex with boron. The absorbance of this ture, add 20 mL salicylaldehyde and stir vigor­ complex is measured colorimetrically at 410 nm ously overnight (12 h). Centrifuge (2,000 rpm, (Basson and others, 1969; Basson and others, 20 min) to separate the azomethine H (orange 1974; Spencer and Erdmann, 1979). Inter­ product) and wash 2 to 3 times with ethanol. ferences from iron and zinc are minimized by Dry to constant weight at 100° C for 3 h and addition of diethylenetriamine pentaacetic acid store in a desiccator. (DTPA). Interferences from bicarbonate are 5.3 Azomethine H reagent: Dissolve 4.5 g eliminated by careful acidification to pH 3 to 5. azomethine H and 10 g ascorbic acid (analytical grade) in 500 mL of demineralized water with 3. Interferences gentle heating. Filter, with suction, through Iron, zinc, and bicarbonate interfere at con­ Whatman No. 40 filter paper. Store in a dark centrations above 400 /ig/L, 2000 /ig/L, and 150 plastic bottle. Hydrolysis of this compound, mg/L, respectively in the absence of pretreat- and, consequently, of baseline drift, is mini­ ment with DTPA and acidification. mized by placing this reagent bottle in a beaker containing a mixture of ice and water during 4. Apparatus analysis. This reagent should be prepared daily 4.1 Technicon AutoAnalyzer consisting of a for optimal results. sampler, proportioning pump, manifold, colori­ 5.4 Boron standard solution /, 1.00 mL= meter, voltage stabilizer, recorder, and printer. 0.100 mg B: Dissolve 0.5720 g high-purity 4.2 With this equipment the following H3BO3, dried over desiccant for 24 h, in demin­ operating conditions have been found satisfac­ eralized water and dilute to 1000 mL. Store in tory for the range 10 to 400 /ig/L: plastic bottle. Absorption cell ——— 50 mm 5.5 Boron standard solution //, 1.00 mL= Wavelength ————— 410 nm 0.010 mg B: Dilute 100.0 mL boron standard Cam —————————— 30/h(2/l) solution I to 1,000 mL with demineralized water. Store in plastic bottle. 5. Reagents 5.6 Boron standard solution III, 1.00 mL= 5.1 Ammonium acetate buffer. Dissolve 0.001 mg B: Dilute 100.0 mL boron standard 99 100 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS solution II to 1,000 mL with demineralized 6. Procedure water. Store in plastic bottle. 6.1 Set up manifold (fig. 17). 5.7 Boron working standards: Prepare a 6.2 Initially feed reagents with demineral­ blank and 500 mL each of a series of boron ized water in the sample line through the working standards by appropriate quantitative system and allow approx 30 min for stabili­ dilution of the boron standard solutions (II and zation of the baseline and instrument warmup. III) as follows: Adjust baseline to read 5 chart divisions on the recorder (25 j*g/L on printer). It is necessary to Boron standard solutions Boron concentration ______(mL)______include the reference channel in the manifold to 0.0 0.0 compensate for baseline drift due to hydrolysis 5.0 of III 10.0 of the azomethine H. 15.0 of III 30.0 6.3 Place a complete set of standards and a 25.0 of III 50.0 50.0 of III 100.0 blank in the first positions of the first sample 100.0 of III 200.0 tray, beginning with the most concentrated 15.0 of II 300.0 20.0 of II standard. Place individual standards of differ­ 400.0 ing concentrations in every eighth position of 5.8 Brij-35 solution, 30-percent aqueous solu­ the remainder of this and subsequent sample tion (Baker Cat. No. C706 or equivalent). trays. Fill remainder of each sample tray with 5.9 DTPA reagent, 0.05M: Suspend 19.7 g samples. Use plastic sample cups to avoid pos­ DTPA in appro* 900 mL demineralized water. Add sible boron contamination from glass con­ 5Af NaOH until pH is 5 to 6, and continue stir­ tainers. ring until all the DTPA dissolves. Add 6 mL 30- 6.4 Begin analysis. When the peak from the percent Brij-35 solution; dilute to 1 liter and filter. highest standard appears on the recorder,

ID mL/min

0 045 in 0 60 Waste To sample r4 *- 0.090 2.90 wash rece 0.030 0 32 Air 20-turn coils 1 0040 0.62 —— Water '(JU* 0.030 0.32 |g|(JL^'(JLr \ —— DTPA 0.040 0.62 0035 042 37-turn delay coil 157-0225-F To waste < ~^J±- Colorimeter R eference channel 410 nm __._50 mm cells S ample channel To waste

0 035 0 42 }> 0.040 0.62 0.030 0 32 —— DTPA 0.030 0 32 Air f \ f \ 1 . ksuu (JD t fcgJI 20-turn co is f ^ * Sampler * Sampler 4 0.065 1.60 ———————— 30/h 37-turn » Itebubbler 0.045 080 delay coil <— waste 2/ 1 cam 157-0225-F 0.051 1.00 To

Figure 17.—Boron, azomethine H manifold METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 101 adjust the STD CAL control until the printer values of 16 and 329 jig/L and standard devi­ reads 425 ptg/L on the 0- to 500-^g/L range. ations of 3 and 5 jig/L respectively. 9.2 Precision also may be expressed in terms 7. Calculations of the percent relative standard deviation as 7.1 Obtain concentration of sample direct­ follows: ly from the printer and correct for the baseline reading. Number of Mean Relative standard deviation 7.2 Alternatively, prepare an analytical replicates _____(percent)______curve by plotting the height of each standard 12 16 19 peak, minus the baseline drift, versus the re­ 12 329 2 spective boron concentration. Obtain the boron concentration of each sample by comparing its References corrected reading to the analytical curve. Basson, W. D., Bohmer, R. G., and Stanton, D. A., 1969, 8. Report Automated procedure for the determination of boron 8.1 Report boron, dissolved (01020), concen­ in plant tissue: Analyst, v. 94, p. 1135-1141. trations as follows: less than 100 j*g/L, nearest Basson, W. D., Pille, P. P., and DuPreez, A. L., 1974, 10 /ig/L; 100 jug/L and above, two significant Automated in situ preparation of azomethine H and the figures. subsequent determination of boron in aqueous solution: Analyst, v. 99, p. 168-170. Spencer, R. R., and Erdmann, D. E., 1979, Azomethine H 9. Precision colorimetric method for determining dissolved boron in 9.1 Analysis of 12 replicates of two test sam­ water: Environmental Science and Technology, v. 13, ples by a single laboratory resulted in mean p. 954-56.

Boron, colorimetric, curcumin

Parameters and Codes: Boron, dissolved, 1-1112-85 fcig/L as B): 01020 Boron, total recoverable, 1-3112-85 (pg/L as B): 01022 Boron, suspended recoverable, 1-7112-85 (pg/L as B): 01021

1. Application Filter the final solution or pass the original sam­ 1.1 This method may be used to analyze ple through a column of strongly acidic cation- water and water-suspended sediment contain­ exchange resin in the hydrogen form to remove ing at least 100 jig/L of boron. The optimum the interfering cations. The latter procedure range for the method on undiluted or unconcen- enables application of the method to waters and trated samples is from 100 to 1,000 /ig/L. effluents of high hardness or solids content. 1.2 Suspended recoverable boron is calcu­ lated by subtracting dissolved boron from total 4. Apparatus recoverable boron. 4.1 Evaporating dish, 100- to 150-mL capaci­ 1.3 Total recoverable boron in water-sus­ ty, of Vycor glass, platinum, or other suitable pended sediment needs to undergo a prelimi­ material. nary digestion-solubilization by method 1-3485 4.2 Ion-exchange column, 50-cm long by before being determined. 1.3-cm diameter. 4.3 Spectrometer, for use at 540 nm, and 2. Summary of method cells with a minimun light-path length of 1 cm. 2.1 When a sample of water containing 4.4 Refer to manufacturer's manual to op­ boron is acidified and evaporated in the pres­ timize instrument. ence of curcumin, a red-colored product, called 4.5 Water bath, 55±2°C. rosocyanine, is formed. The rosocyanine is ex­ tracted into a suitable solvent and the red color, 5. Reagents which has a maximum absorbance at 540 nm, 5.1 Boron standard solution /, 1.00 mL=100 is measured spectrometrically. jig B: Dissolve 0.5720 g high-purity H3BO3, 2.2 The method is identical to that found in dried over desiccant for 24 h, in demineralized "Standard Methods for the Examination of water and dilute to 1000 mL. Store in plastic Water and Wastewater" (American Public bottle. Health Association and others, 1980). 5.2 Boron standard solution II, 1.00 L=1.00 /ig B: Dilute 10.0 mL boron standard solution 3. Interferences I to 1,000 mL with demineralized water. Store 3.1 Nitrate-nitrogen concentrations greater in plastic bottle. than 20 mg/L interfere. 5.3 Cation-exchange resin: Load the column 3.2 Significantly high results are possible with a strongly acidic cation-exchange resin. when the total of calcium and magnesium hard­ Backwash the column with demineralized water ness exceeds 100 mg/L as calcium carbonate. to remove entrained air bubbles. Henceforth, Moderate hardness levels also can cause a make certain the resin remains covered with considerable percentage error in the low boron liquid at all times. Pass 50 mL 2Af HC1 through range. The interference arises from the insolu­ the column at a rate of 0.2 mL/min of acid per bility of the hardness salts in 95-percent ethanol milliliter of resin in column and then wash it free and consequent turbidity in the final solution. of acid with demineralized water. The frequency 103 104 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS of regeneration depends on the mineral content usually sufficient for complete drying and of the samples. removal of HC1. Keep drying time constant for 5.4 Curcumin reagent: Dissolve 40 mg fine­ standards and samples. ly ground curcumin (Eastman No. 1179 or 6.7 After the dishes cool to room tempera­ equivalent) and 5.0 g oxalic acid in 80 mL ture, add 10.0 mL 95-percent ethanol to each 95-percent ethanol. Add 4.2 mL concentrated dish, stirring gently with a polyethylene rod to HC1 (sp gr 1.19) and dilute to 100 mL with ensure complete dissolution of the red-colored ethanol. The reagent is stable for several days product. if stored in a refrigerator. 6.8 Wash the contents of each dish into a 5.5 Ethanol, 95-percent. 25-mL volumetric flask using 95-percent 5.6 Hydrochloric acid, 2M: Mix 166 mL ethanol and adjust to volume with ethanol. Mix concentrated HC1 (sp gr 1.19) with demineral- by repeated inversion (NOTE 3). ized water and dilute to 1 L. NOTE 3. If the final sample solution is turbid, filter through No. 30 Whatman filter paper or 6. Procedure equivalent. 6.1 Precautions: Exercise close control of 6.9 Determine the absorbance of samples variables, such as volumes and concentrations and standards against the blank. Complete all of samples, standards, and, reagents, as well as absorbance readings within 1 h of drying the time and temperature of drying. Use evaporat­ samples. ing dishes identical in shape, size, and compo­ sition to insure equal evaporation time. 7. Calculations Increasing the time of evaporation results in 7.1 Determine the micrograms boron in the intensification of the resulting color. sample solution from a plot of absorbances of 6.2 For samples having high hardness (100 standards. mg/L CaCO3 or more), proceed as follows 7.2 Determine the dissolved or total-recover­ (NOTE 1): Pipet 25 mL of sample solution or able boron concentration in micrograms per liter of a smaller sample of known high boron con­ as follows: tent diluted to 25 mL onto the resin column. Ad­ just the rate of flow through the column to 1,000 X jig B in sample. about 2 drops per second and collect the effluent B —————- ——— -———— in a 50-mL volumetric flask. Wash the column mL sample with small portions of demineralized water un­ til the flask is full to the mark and mix. 7.3 To determine micrograms per liter of NOTE 1. For samples containing less than 100 suspended recoverable boron, subtract dis- mg/L hardness as CaCO3, start with paragraph solved-boron concentration from total-recover­ 6.3. able-boron concentration. 6.3 Pipet 1.00 mL of sample solution con­ taining less than 1.0 jig B into an evaporating 8. Report dish (NOTE 2). Report boron, dissolved (01020), total-recover­ NOTE 2. If the sample contains more than able (01022), and suspended-recoverable (01021), 1,000 Mg/L B, make an appropriate dilution with concentrations as follows: less than 1,000 /tg/L, demineralized water, so that a 1.00-mL portion nearest 100 /tg/L; 1,000 /*g/L and above, two sig­ contains approx 0.50 jig B. nificant figures. 6.4 Prepare in evaporating dishes a blank and sufficient standards (1.0 fig B max) and ad­ 9. Precision just the volume of each to exactly 1.0 mL with 9.1 The standard deviation for dissolved demineralized water. boron within the range of 65 to 643 pglL for 16 6.5 Add 4.0 mL curcumin reagent to each samples was found to be independent of con­ and swirl each dish gently to mix contents. centration. The 95-percent confidence interval 6.6 Float the dishes on a water bath set at for the average standard deviation of 63.4 pg/L 55±2°C and let them remain for 80 min, a time ranged from 54.2 to 76.3 /ig/L. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 105 9,2 Precision for dissolved boron for four 9.3 It is estimated that the percent relative of the 16 samples expressed in terms of the standard deviation for total recoverable and percent relative standard deviation is as suspended recoverable boron will be greater follows: than that reported for dissolved boron.

Number of Mean Relative standard deviation laboratories _____(percent)____ Reference 4 65 37 5 98 60 American Public Health Association and others, 1980, 4 320 20 Standard methods for the examination of water and 6 643 10 wastewater (15th ed.): Washington, D.C., p. 257.

Boron, colorimetric, dianthrimide Parameters and Codes: Boron, dissolved, 1-1110-85 <^g/L as B): 01020 Boron, total recoverable, 1-3110-85 OiQ/L as B): 01022 Boron, suspended recoverable, 1-7110-85 (pg/L as B): 01021 Boron, recoverable-from-bottom-material, dry wt, 1-5110-85 (/*g/g as B): 01023

1. Application 3. Interferences 1.1 This method may be used to analyze 3.1 Traces of moisture will precipitate the water and water-suspended sediment contain­ reagent and interfere in the determination; ing between 20 and 1,000 /*g/L of boron. Sam­ therefore, precautionary measures given in the ple solutions containing more than 1,000 jig/L procedure must be followed precisely. Nitrate need to be diluted. and bicarbonate interfere with color develop­ 1.2 Suspended recoverable boron is calcu­ ment and must be removed by volatilization as lated by subtracting dissolved boron from total nitric acid and carbon dioxide in the presence recoverable boron. of sulfuric acid. Organic matter in high concen­ 1.3 This method may be used to analyze bot­ trations chars and causes a discoloration of the tom material containing at least 10 /*g/g of complex, but this interference is easily recog­ boron. If the sample solution prepared for nized; small quantities of organic material cause analysis contains more than 250 jig boron, a por­ no trouble. Some success in removal of the tion of it needs to be diluted before analysis. organic-material interference has been obtained 1.4 Total recoverable boron in water-sus­ by heating the sample in the presence of pended sediment needs to undergo preliminary hydrogen peroxide for 1 to 2 h, but all nascent digestion-solubilization by method 1-3485, and oxygen must be volatilized before the dian­ recoverable boron in bottom material needs to thrimide is added to the sample. When perox­ undergo preliminary digestion-solubilization by ide digestion is used, the final color complex method 1-5485 before being determined. should be compared with standard boron solu­ 1.5 This method is not suitable for samples tions similarly treated. Oxidizing and reducing containing high concentrations of oxidizing or constituents also interfere. Do not use glass­ reducing materials or dissolved organic matter. ware cleaned with chromic-sulfuric acid. However, it is not affected by buffering mate­ 3.2 Some boric acid is probably volatilized during evaporation of the sample in the pres­ rials or high concentrations of total salts. ence of sulfuric acid. Prolonged heating or temperatures higher than that recommended 2. Summary of method volatilize an excessive amount of boron and Boron, when heated with 1,1'-dianthrimide in decrease the sensitivity of the test. The loss of concentrated sulfuric acid, gives a colored com­ boron is proportional to the boron content of the plex (Ellis and others, 1949; Rainwater, 1959). sample or standard; hence, such loss in no way The color change ranges from greenish yellow affects the linearity of the color development if to blue. The reaction producing the blue color the heating is uniform. Nonlinearity of the depends on the temperature and duration of concentration-versus-absorbance curve can heating and on the concentrations of reagent result from weak reagents. The standards in and of boron. Maximum color development is step 6.2 of the procedure act as a check on achieved after the reaction has proceeded for 3 linearity of the reaction and on the suitability h at 90 °C. of the working reagent. 107 108 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 4. Apparatus add 10.0 mL concentrated H2SO4, Mix careful­ 4.1 Oven, 90 °C: Uniformity of temperature ly with a stirring rod or test-tube mixer. throughout the oven is imperative. 6.8 Determine the absorbance of each sam­ 4.2 Spectrometer, for use at 620 run. ple and standard against the blank. 4.3 Refer to the manufacturer's manual to optimize instrument. 7. Calculations 7.1 Determine the micrograms boron in each 5. Reagents sample solution from a plot of absorbances of 5.1 Boron standard solution I, 1.00 mL=100 standards. fig B: Dissolve 0.5720 g high-purity H3BO3, 7.2 Determine the dissolved or total-recover­ dried over desiccant for 24 h, in demineralized able-boron concentration in micrograms per liter water and dilute to 1000 mL. Store in plastic as follows: bottle. 5.2 Boron standard solution II, 1.00 mL= 1,000 X Mg B in sample 1.0 jig B: Dilute 10.0 mL boron standard solu­ B tion I to 1,000 mL with demineralized water. mL sample Store in plastic bottle. 5.3 1,1 '-Dianthrimide (or1,1 '-iminodianthra- 7.3 To determine micrograms per liter of quinone) solution I, 200 mg per 50 mL concen­ suspended recoverable boron, subtract dis- trated H2SO4: Dissolve 200 mg l.l'-dianthri- solved-boron concentration from total-recover­ mide in 50 mL concentrated H2SO4 (sp gr 1.84). able-boron concentration. The reagent is stable for a long period if the con­ 7.4 Determine the boron concentration in tainer is sealed and refrigerated. Store in Teflon micrograms per gram in bottom material as bottle. follows: 5.4 l,l'-Dianthrimide solution II, (1 + 19): Dilute 1 volume of l,r-dianthrimide solution I Mg B in sample X mL of original digest with 19 volumes of concentrated H2SO4 (sp gr B(/ig/g)= 1.84). The reagent is stable for a long period if wt of sample (g)XmL sample the container is sealed and refrigerated. Store in Teflon bottle. 8. Report 5.5 Sulfuric acid, concentrated (sp gr 1.84). 8.1 Report boron, dissolved (01020), total- recoverable (01022), and suspended-recoverable 6. Procedure (01021), concentrations as follows: less than 100 6.1 Pipet a volume of sample solution con­ jig/L, nearest 10 jig/L; 100 /ig/L and above, two taining less than 5.0 Mg B (5.0 mL max) into a significant figures. Pyrex test tube, and adjust volume to 5.0 mL. 8.2 Report boron, recoverable-from-bottom- 6.2 Prepare a blank of demineralized water material (01023), concentrations as follows: less and sufficient standards, and adjust the volume than 100 jig/g, nearest 10 ng/g; 100 jig/g and of each to 5.0 mL. above, two significant figures. 6.3 Cautiously add 1.0 mL concentrated H2SO4 and mix by swirling the contents of the 9. Precision tube. Use of a test-tube-vibrating mixer is 9.1 The standard deviation for dissolved helpful. boron within the range of 20 to 530 /*g/L for 16 6.4 Evaporate for at least 40 h in an oven samples was found to be independent of concen­ at 90 °C. At the end of the evaporation, the solu­ tration. The 95-percent confidence interval for tion volume should be between 1.0 and 0.5 mL. the average standard deviation of 37.2 jig/L 6.5 Add 5.0 mL l,l'-dianthrimide solution II ranged from 31.2 to 46.1 j*g/L. and mix by swirling. 9.2 Precision for dissolved boron for five of 6.6 Heat in oven for 3 h at 90 °C. the 16 samples expressed in terms of the per­ 6.7 Immediately after cooling, with caution cent relative standard deviation is as follows: METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 109 Number of Mean Relative standard deviation recoverable boron in bottom material will be laboratories (percent) greater than that reported for dissolved boron. 5 20 105 6 101 17 5 222 24 References 3 423 3 4 530 12 Ellis, G. H., Zook, £. G.t and Baudisch, Oskar, 1949, Colon* metric determination of boron using l.l'-dianthrimide: Analytical Chemistry, v. 21, p. 1345-8. 9.3 It is estimated that the percent relative Rainwater, F. H.t 1959, Determination of boron with 1,1'* standard deviation for total recoverable and dianthrimide: Am«rirjm Water Works Association Jour­ suspended recoverable boron and for total nal, v. 51, p. 1046-50.

Bromide, titrimetric, hypochlorite oxidation

Parameter and Code: Bromide, dissolved, 1-1125-85 (mg/L as Br): 71870

1. Application 3. Interferences This method may be used to analyze any Iron, manganese, and organic material in­ natural or treated water or brine containing at terfere with the basic reactions of the method, least 1.0 mg/L of bromide. Highly concentrated but their interferences are removed by prelim­ brines may require dilution. inary treatment with calcium oxide.

2. Summary of method 4. Apparatus 2.1 The determination of bromide involves 4.1 Buret, 10-mL capacity. the determination of bromide and iodide collect­ 4.2 Iodine flasks, 250-mL capacity. ively, and then the determination of iodide alone; bromide is calculated by difference. 5. Reagents Bromide and iodide are oxidized to bromate and 5.1 Acetic acid, 2.2M: Mix 125 mL glacial iodate, respectively, by hypochlorite, and the HC2H3O2 (sp gr 1.069) with demineralized excess hypochlorite is subsequently decom­ water and dilute to 1 L. posed with sodium formate (Kolthoff and 5.2 Bromine water, saturated: Add to ap- others, 1969). prox 250 mL demineralized water slightly more liquid Br2 than will dissolve when mixed. Store 3OC1-1 + Br'1 l + 3C1'1 in a glass-stoppered, actinic-glass bottle. 5.3 Calcium carbonate, powder, CaCO3. 3OC1-1 + I-1 1 + 3CH 5.4 Calcium oxide, anhydrous powder, CaO. 5.5 Hydrochloric acid, 6M: Mix 50 mL Iodine equivalent to the combined iodate and concentrated HC1 (sp gr 1.19) with demineral­ bromate is then liberated by addition of ized water and dilute to 100 mL. potassium iodide to an acid solution. 5.6 Methyl red indicator solution, 0.01 g/100 mL: Dissolve 0.01 g water-soluble methyl red BrOg1 + 6I-1 + 6H+1 -» 3I2 + 3H2O + Br-1 in 100 mL demineralized water. 5.7 Potassium fluoride, crystals, KF*2H2O. lOg1 + 5I-1 + 6H+1 -* 3I2 + 3H2O 5.8 Potassium hypochlorite solution, 4.4 g/L: Dissolve 6.2 g KOH in 100 mL demineralized The liberated iodine is titrated with standard water; then saturate the solution with bromine- thiosulfate with use of starch as the indicator. free C12 while continually cooling and stirring. Store in a glass-stoppered, actinic-glass bottle. I2 + 2S2O§2 -> S4Oe2 + 2I-1 Prepare fresh daily. 5.9 Potassium iodide, crystals, lO^-free: 2.2 Iodide alone is determined by oxidation The KI can be tested for IO§X by dissolving to iodate with bromine in a buffered solution. about 0.1 g in 5 mL demineralized water, acidi­ Iodine equivalent to the iodate is then liberated fying with 1 or 2 drops concentrated H2SO4 (sp from added potassium iodide and titrated with gr 1.S4), sand adding 2 to 3 mL starch indicator thiosulfate as in the combined determination. solution. Immediate appearance of a blue color 111 112 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS indicates the presence of lOjj1; slow color form­ 6. Procedure ation is due to atmospheric oxidation. 6.1 Remove soluble iron, manganese, and 5.10 Sodium acetate solution, 165 g/L: organic matter by adding a slight excess of CaO Dissolve 273 g NaC2H3O2-3H2O in demineral- to approx 400 mL sample; mix, let stand about ized water and dilute to 1 L. 1 h, and filter through a dry, moderately reten­ 5.11 Sodium chloride, crystals: Free from I'1, tive filter paper. Discard the first 75 mL of lOg1, Br-1, and BrOg1. The NaCl can be tested filtrate. for lOg1 and BrOjj1 by dissolving about 0.1 g 6.2 For the combined Br~x and I'1 determin­ in 5 mL demineralized water, acidifying with 1 ation, pipet a volume of the filtrate containing or 2 drops concentrated H2SO4 (sp gr 1.84), and less than 5.0 mg Br'1 and I'1 (100.0 mL max) adding 2 to 3 mL starch indicator solution. Im­ into a 250-mL iodine flask, and adjust the mediate appearance of a blue color indicates volume to approx 100 mL. presence of lOjj1 or BrOjj1; slow color formation 6.3 Prepare a blank of approx 100 mL is caused by atmospheric oxidation. demineralized water, and carry it through the 5.12 Sodium formate solution, 50 g/100 mL: procedure along with the sample. Dissolve 50 g NaHCO2 in hot demineralized 6.4 Add sufficient NaCl to produce a 3.0 g water and dilute to 100 mL. Prepare fresh daily. Cl"1 content. 5.13 Sodium molybdate solution, 1.0 g/100 6.5 Add a drop of methyl red indicator solu­ mL: Dissolve 1.2 g Na2MoO4-2H2O in demin­ tion, and make the solution just acidic with 6M eralized water and dilute to 100 mL. HC1. 5.14 Sodium thiosulfate solution, 0.10AT: 6.6 Add 10 mL KC1O solution, 0.5 mL 6M Dissolve 25.0 g Na2S2O3-5H2O in carbon diox­ HC1, and sufficient CaCO3 to produce an excess ide-free, demineralized water; add 1 g Na2CO3 of approx 0.1 g. and dilute to 1 L. 6.7 Heat the solution to boiling and main­ 5.15 Sodium thiosulfate standard solution, tain this temperature for about 8 min. 0.010JV: Dilute 100.0 mL O.lOtf Na2S2O3 solu­ 6.8 Reduce the excess KC1O by adding 2 mL tion to 950 mL with carbon dioxide-free, NaHCO2 solution, taking precaution to wash demineralized water and standardize against down the sides of the flask with a small amount KIO3 as follows: Dry approx 0.5 g KIO3 for 2 of hot water. Keep the solution hot for an addi­ h at 180 °C. Gool and dissolve 0.3567 g in tional 8 Tnfn. demineralized water, and dilute to 1,000 mL. 6.9 Cool and add several drops of Na2MoO4 Pipet 25.00 mL of the KIO3 solution into a solution. If any iron precipitates at this point, 250-mL iodine flask; then add successively 75 add 0.5 g KF-2H2O. mL demineralized water and 0.5 g KI crystals. 6.10 Add approx 1 g KI and 10 mL 3.6M After solution is complete, add 10 mL 3.6M H2SO4, and let stand 5 min in the dark. H2SO4. Allow the stoppered flask to stand 5 6.11 Titrate the liberated I2 with O.OIN min in the dark, and then titrate with standard Na2S2O3 standard solution, adding 2 to 3 mL Na2S2O3 solution, adding 2 mY. starch indicator starch indicator solution as the end point is ap­ solution as the end point is approached (light proached. Disregard a return of the blue color straw color). after the end point has been reached. 6.12 For the I"1 determination, pipet a 0.25 volume of filtrate (step 6.1) containing less Normality of Na2S2O3= than 5.0 mg I'1 (100.0 mL max) into a 250-mL Na2S2O3 iodine flask, and adjust the volume to approx 100 mL. 5.16 Starch indicator solution, stable or 6.13 Prepare a blank of 100.0 mL demineral­ "thyodene," powdered (Fisher No. T138 or ized water and carry through the procedure equivalent). along with the sample. 5.17 Sulfuric acid, 3.6M: CAUTIOUSLY add 6.14 Add a drop of methyl red indicator solu­ 200 mL concentrated H2SO4 (sp gr 1.84) to tion, and make the solution just acidic with demineralized water, cool, and dilute to 1 L. 3.6M H2S04. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 113 6.15 Add 15.0 mL NaC2H3O2 solution, 5.0 where mL 2.2M HC2H3O2, and sufficient bromine epL= equivalents per liter, water to produce a light-yellow color; mix and allow to stand 5 min. mL^= titrant volume for blank determin­ 6.16 Reduce the excess Br2 by adding ation, NaHCO2 solution drop by drop until the yellow mLt= titrant volume for combined determin­ tinge in the sample disappears; then add an ex­ cess of 1 mL. ation, 6.17 Wash the sides of the flask with a small and amount of water, and blow out Br2 vapors with .= titrant volume for I-1 determination. a syringe and a glass tube inserted into the mouth of the flask. If any iron precipitates at 8. Report this point, add 0.5 g KI-2H2O. Report bromide, dissolved (71870), concentra­ 6.18 Add approx 1 g KI and 10 mL 3.6Af H2SO4, and let stand 5 min in the dark. tions as follows: less than 10 mg/L, one decimal; 6.19 Titrate the liberated I2 with 0.01CW 10 mg/L and above, two significant figures. Na2S2O3 standard solution, adding 2 to 3 mL starch indicator solution as the end point is ap­ 9. Precision proached (light-straw color). Disregard a return Single-operator precision of this method (American Society for Testing and Materials, of the blue color after the end point has been 1984) may be expressed as follows: reached.

7. Calculations S0 = 0.0044X 7.1 Determine 1 in epL as follows: where Br-i+I-i(epL)= S0= single-operator precision, milligrams per liter, 1,000 0.01 —————— X —— X (mLrmL6) and mL sample 6 X= concentration of bromide, milligrams per 7.2 Determine I'1 in epL as follows: liter. References I~1„(epL)=————— T 1,000 X ——0.01 X(mL,-mLb). mL sample 6 American Society for Testing and Materials, 1984, Annual book of ASTM standards, section 11, water: Phila­ delphia, v. 11.01, p. 482-90. 7.3 Determine Br"1 in mg/L as follows: Kolthoff, I* MM Sandell, E, B., Meehan, E. J., and Bracken- stein, S., 1969, Quantitative chemical analysis (4th ed.): Br-1(mg/L)=79.91X[epL (I~i+ Br'M-epL I"1 New York, Macmillan, 1199 p.

Bromide, ion-exchange chromatographic, automated

Parameters and Codes: Bromide, dissolved, 1-2057-85 (mg/L as Br): 71870 Bromide, dissolved, 1-2058-85 (mg/L as Br): 71870

2. Summary of method measured using an electrical-conductivity Bromide is determined sequentially with cell. See method 1-2057, anions, ion-ex­ six other anions by ion-exchange chroma- change chromatographic, automated, and tography. Ions are separated based on their method 1-2058, anions, ion-exchange chro­ affinity for the exchange sites of the resin. matographic, low ionic-strength water, The separated anions in their acid form are automated.

115

Bromide, ion-exchange chromatographic-electrochemical, automated

Parameter and Code: Bromide, dissolved, 1-2128-85 (mg/L as Br): 71870

1. Application containing greater than 2,000 mg/L of chloride 1.1 This method may be used to analyze at­ must first be diluted. mospheric precipitation and natural water con­ 3.2 Sulfite elutes at almost the same time as taining at least 0.01 mg/L of bromide. Samples bromide, however, this interference will not af­ containing more than 1 mg/L need to be diluted. fect bromide since any sulfite in the sample will 1.2 Analyses need to be performed on have had time to oxidize to sulfate before anal­ filtered and unacidified samples. ysis. For example, 10 mg/L of sulfite usually ox­ idizes to sulfate within 120 h. 2. Summary of method Bromide is determined with an ion chromato- 4. Apparatus graph using an ion-exchange resin in combin­ 4.1 Ion Chromatograph, Dionex Model 12 or ation with a specific eluent to separate the equivalent, using the following operating con­ anions. After the solution has passed through ditions: the separator column, the sample stream flows Sample loop ————— 200 ML through an electrochemical cell, where a fixed Eluent flow rate —— 138 mL/h (30 potential is applied. Any electroactive species percent of such as bromide having an oxidation-reduction full capacity) potential near the applied potential will gen­ Sample pump flow rate 50 percent of erate a current, which is directly proportional full capacity to the concentration of the electroactive 4.1.1 Precolumn, 4X50 mm, fast-run, anion- species. resin column (Dionex P/N 030831 or equivalent) placed before the separator column to protect 3. Interferences the separator column from being fouled by par- 3.1 Chloride is an interference. When chlor­ ticulates or species strongly retained by the ion- ide ion passes through the detector, a current exchange resin. generates because of the formation of silver 4.1.2 Separator column, 4X250 mm, fast-run, chloride on the surface of the silver-working anion separator column packed with low-capac­ electrode. The eluent stream, which removes ity, pellicular, anion-exchange resin (Dionex P/N silver chloride, generates a negative peak. The 030830 or equivalent) that is styrene divinyl- higher the chloride concentration, the longer it benzene based. This has been found to be suit­ takes for the peak to return to baseline condi­ able for resolving fluoride, chloride, nitrite, tions. The effects of chloride at various levels orthophosphate, bromide, nitrate, and sulfate. of bromide are shown in tables 5 and 6. Chloride 4.2 Pulse damper, installed just before the interferes with bromide if the chloride-to- injection valve to reduce flow pulsation. bromide ratio is greater than 1,000:1 for the 4.3 Electrochemical detector, Dionex or analytical range of 0.01 to 0.1 mg/L of bromide. equivalent, consisting of cell and potentiostat. A similar interference is present when the 4.3.1 The electrochemical cell is installed after chloride-to-bromide ratio exceeds 5,000:1 for the the separator ion-exchange column. The cell 0.1 to 1.0 mg/L analytical range. Samples is composed of a silver-working electrode, a 117 118 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Table 5.—Recovery of bromide in the presence of chloride for 0.01 to 0.09 mg/L bromide

Chloride (mg/L) 10 20 30 50 70 90 Bromide Recovery of bromide (mg/L) (percent) 0.01 100 90 50 40 10 0 .02 100 100 65 50 50 35 .03 100 100 100 80 67 40 .05 100 100 100 100 80 80 .07 100 100 100 100 100 86 .09 100 100 100 100 100 100

Table 6.—Recovery of bromide in the presence of chloride for 0.01 to 0.09 mg/L bromide

Chloride (mg/L)

500 700 1000 1500 2000 2500 Bromide Recovery of bromide (mg/L) (percent) 0.1 100 80 70 10 0 0 .2 100 100 100 75 50 10 .3 100 100 100 100 70 17 .4 100 100 100 100 100 28 .5 100 100 100 100 100 50 .6 100 100 100 100 100 53 .7 100 100 100 100 100 57 .8 100 100 100 100 100 60 .9 100 100 100 100 100 61 stainless steel counter electrode and a Ag/AgCl Applied potential — 0.10 V (NOTE 2) reference electrode (NOTE 1). CAUTION: Select mode MEAS - ON Samples containing oil and grease damage the Select mode +/- — + membrane. Off set multiplier —— XI uA Meter select ———— Out Put NOTE 1. It is necessary to refill the reference Output range ———— 100 nA/V electrode with NaCl solution saturated with NOTE 2. The applied potiential setting of the AgCl and to replace the ion-exchange membrane potentiostat that gives the optimum sensitivi­ and membrane gasket when the potentiostat ty for bromide will vary with age and condition cannot be zeroed (high detector output). This of the reference electrode, and needs to be de­ happens when the AgCl in the reference elec­ termined. trode cell is depleted and (or) the membrane is 4.4 Autosampler, Technicon IV or equiv­ damaged. It is important not to introduce any alent, using a proportioning pump to deliver air bubbles while refilling the reference electrode water to the wash receptacle. and replacing the membrane; this causes a loss 4.5 Integrator, Spectra Physics SP-4100 or of sensitivity. The silver-working electrode equivalent, using the following operating con­ needs to be cleaned once a month. Polish the ditions: surface with a small amount of toothpaste on Bromide Bromide a Kimwipe to remove the gray tarnish, and then 0.01 to 0.1 mg/L 0.1 to 1.0 mg/L rinse with deionized water. It is desirable to Input range 1V 10V have a spare reference electrode to avoid Chart speed 1 cm/min 1 cm/min Calibration 0 (linear) 2 (quadratic fit) downtime. If there is difficulty in refilling the PT (Peak threshold) 60,000 1,500 reference electrode, contact the manufacturer. AT (Attenuation) 512 128 PH (Peak height) 1 1 4.3.2 The potentiostat operating conditions PW (No. of data 60 60 are as follows: samples per bunch) METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 119 4.6 For additional information refer to the starts the integrator at the beginning of each manufacturer's instruction manual. sample injection. 6.3 Press the LEVEL key of the integrator, 5. Reagents which causes the display of the input voltage. 5.1 Bromide standard solution /, 1.00 mL= Level the integrator at 10 mV or display 1000 1.00 mg Br-1: Dissolve 1.2877 g NaBr in demin- by adjusting coarse dial of potentiostat. eralized water and dilute to 1,000 mL. 6.4 Press the PT EVAL (peak threshold 5.2 Bromide standard solution II, 1.00 mL= evaluation) key for integrator to evaluate the 0.01 mg Br-1: Dilute 10.0 mL bromide stand­ detector signal for noise and drift. ard solution I to 1,000 mL with demineralized 6.5 Create an information file in the in­ water. tegrator by pressing the DIALOG key. Create 5.3 Bromide standard solution III, 1.00 File 1 for bromide concentrations between 0.1 mL= 0.001 mg Br-1: Dilute 100 mL bromide to 1.0 mg/L using a quadratic fit. Create File standard solution II to 1,000 mL with 2 for bromide concentrations less than 0.1 mg/L demineralized water. using a single-point calibration with intercept of zero. 5.4 Bromide working standards: Prepare 6.6 Place a complete set of standards in the 1,000 mL each of a series of bromide working first positions of the tray, beginning with the standards by appropriate quantitative dilution least concentrated standard, followed by sam­ of bromide standard solutions II and III. ples. Place individual standards of differing concentrations in every tenth position of the re­

Bromide standard solutions Bromide concentration mainder of the tray. ______(mL)______(mg/L)______10 of III 0.01 7. Calculations 50 of III .05 The integrator automatically computes the 10 of II .1 50 of II .5 concentration of bromide in each sample by 100 of II 1.0 comparing its peak height or peak area to the analytical curve. Retention time for bromide is approximately 5.4 min. 5.5 Eluent, 0.003M sodium bicarbonate- 0.0024M sodium carbonate (NOTE 3): Dissolve 8. Report 0.2520 g NaHCO3 and 0.2544 g Na2CO3 in Report bromide, dissolved (71870), concentra­ demineralized water and dilute to 1 L. tions as follows: less than 1.0 mg/L, nearest 0.01 NOTE 3. Eluent concentration may be varied mg/L; 1.0 mg/L and above, two significant slightly to obtain the same retention times for figures. each anion when a new separator column is used. The NaHCO3 is subject to thermal 9. Precision and accuracy decomposition and must be weighed without 9.1 Analysis of six test samples 10 times prior drying. each by a single operator over a period of one month resulted in the following: 6. Procedure 6.1 Set up ion chromatographic system Standard deviation Relative standard deviation according to manufacturer's instructions. (mg/L) _____(percent)______Equilibrate the column with eluent until a 0.005 1.6 stable baseline is obtained. Allow approx 30 min .005 2.2 .005 2.2 for equilibration. .008 2.6 6.2 Enter appropriate program into the .008 1.6 main program controller of the ion chromato- .002 4.7 graph according to the manufacturer's instruc­ tion. The system is configured so that the ion 9.2 Recovery of bromide added to ten water chromatograph, controls the autosampler and samples resulted in the following: 120 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Chloride Bromide Bromide Bromide References present present added found Recovery Fishman, M. J., and Pyen, G. S., 1979, Determination of (mg/L) (mg/L) (mg/L) (mg/L) (percent) selected anions in water by ion chromatography: U.S. 31 0.59 0.5 1.13 108 Geological Survey Water-Resources Investigations, 263 .49 .5 1.03 108 79-101, 30 p. 63 .33 .3 .65 107 Johnson, E. LM and Gathers, E., 1981, Applications of 56 .30 ,3 .61 103 simultaneous detection in 1C: 23rd Rocky Mountain 2.28 .22 .3 .51 97 Conference, Denver, Colorado. 5.95 .040 .05 .089 98 4.59 .037 .05 .086 98 Small, H., Stevens, T. S., and Bauman, W. C., 1975, Novel 4.78 .031 .03 .062 103 ion exchange chromatographic method using conduc- 4.89 .029 .01 .039 100 timetric detection: Analytical Chemistry, v. 47, 5.05 .031 .03 .064 110 p. 1801-09. Bromide, colorimetric, fluorescein, automated-segmented flow

Parameter and Code: Bromide, dissolved, 1-2129-85 (mg/L as Br): 71870

1. Application Absorption cell ——— 50 mm This method may be used to analyze natural Wavelength ————— 520 nm water containing from 0.010 to 0.40 mg/L of Cam —————————— 30/h (2/1) bromide. Samples containing greater concentra­ tions need to be diluted. 5. Reagents 5.1 Bromide standard solution /, 1.00 mL= 2. Summary of method 0.100 mg Br'1: Dissolve 0.149 g KBr, dried The sample is buffered to pH 5.6 with an overnight over concentrated H2SO4, in acetic acid buffer solution and then reacted with demineralized water and dilute to 1,000 mL with chloramine T to oxidize the bromide to hypo- demineralized water. bromous acid. The hypobromous acid formed 5.2 Bromide standard solution II, 1.00 mL= then reacts with fluorescein to form the pink 0.010 mg Br-1: Dilute 100.0 mL bromide stand­ eosin (tetrabromo fluorescein), which is propor­ ard solution I to 1,000 mL with demineralized tional to the bromide concentration. water. 5.3 Bromide working standards: Prepare a Br-1 + HOC1 -* BrOH + Cl'1 blank and 1000 mL each of a series of bromide working standards by appropriate quantitative BrOH + Fluorescein -*> Tetrabromo dilution of bromide standard solution II as Fluorescein (pink) follows:

3. Interferences Bromide standard solution I Bromtde concentration ______

J_ O.OSOIn I Air O.32mL/m in 0.051 In Waste 1.OOmL/m n 20 M O.OSOin Air 50-Turn Turn 0.32mL/m in coil coil col Sample t fvmmn nnnnmci«jr V 0.080 In

> > k I 2.50mL/m in Sampler 4 Buffer 30/h 0.045in 2/1cam o.8OmL/m in O.OIOIn Chloraminc O.O5mL/m tin O.OIOin Fluorescei trimeter To 0.05 mL/r nin nm Wast<* sampler mm cell 1 O.IOOin Water wash 3.40 mL/rnin ^T receptacle 0.051 in Waste L-]= 1.00mL/min | Recorder Proportioning pump

Figure 18.—Bromide, fluorescein manifold METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 123 7.2 Compute the apparent bromide concen­ of percent relative standard deviation is as tration of each sample by comparing its peak follows: height to the analytical curve. Any baseline drift that may occur must be taken into account Number of Concentration Relative standard deviation when computing the height of a sample or replicates (mg/L) ______(percent)_____ standard peak. 10 , 0.010 15.0 10 ' .050 10.0 7.3 Compute the iodide concentration of 10 .100 5.0 each sample in accordance with method I- 2371. 10 .350 2.0 7.4 Compute the bromide concentration as 10 .550 1.8 follows: 10 .860 2.0 Br-1(mg/L)= References mg/L apparent concentration-mg/L iodide concentration Marti, V. C., and Arozarena, C. E., 1981, Automated deter­ mination of bromide in water: Proceedings Pittsburgh 8. Report Conference, No. 734. Thomas, L. C., and Chamberlin, G. J.f 1980, Colorimetric Report bromide, dissolved (71870), concentra­ chemical analytical methods, 9th: England, The Tinto­ tions as follows: less than 0.1 mg/L, two meter Ltd., p. 111-12. decimals; 0.1 mg/L and above, two significant Stenger, V. A., and Kolthorf, I. M., 1935, The detection and figures. colorimetric estimation of micro quantities of bromide: Journal of the American Chemical Society, v. LV11, p. 831-3. 9. Precision Zitomer, F. and Lambert, J. L., 1963, Spectrophotometric Single-operator precision for dissolved determination of bromide ion in water: Analytical bromide for six samples expressed in terms Chemistry, v. 35, p. 1731-34.

Cadmium, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Cadmium, dissolved, 1-1136-85 0*g/L as Cd): 01025 Cadmium, total recoverable, 1-3136-85 (j*g/L as Cd): 01027 Cadmium, suspended recoverable, 1-7136-85 (/ig/l as Cd): 01026

1. Application optimize instrument for the following: 1.1 This method may be used to analyze Grating ———————— Ultraviolet water and water-suspended sediment contain­ Wavelength ————— 228.8 nm ing from 1 to 25 jtg/L of cadmium. Sample solu­ Source (hollow-cathode tions containing more than 25 /ig/L need either or electrodeless-dis- to be diluted prior to chelation-extraction or to charge lamp) ——— Cadmium be analyzed by the atomic absorption spectro­ Oxidant ———————— Air metric direct method. Fuel —————————— Acetylene 1.2 Suspended recoverable cadmium is cal­ Type of flame ———— Oxidizing culated by subtracting dissolved cadmium from 4.3 Different burners may be used according total recoverable cadmium. to manufacturers' instructions. 1.3 Total-recoverable cadmium in water- suspended sediment needs to undergo a prelim­ 5. Reagents inary digestion-solubilization by method 1-3485 5.1 Ammonium pyrrottdine dithiocarbamate before being determined. solution, 1 g/100 mL: Dissolve 1 g APDC in 100 1.4 If the iron concentration of the sample mL demineralized water. Prepare fresh daily. solution exceeds 25,000 /ig/L, determine cad­ 5.2 Cadmium standard solution 7,1.00 mL= mium by the atomic absorption spectrometric 100 jig Cd: Dissolve 0.1000 g Cd splatters in a direct method. TnininrniTn of dilute HNO3. Heat to increase rate of dissolution. Add 10 mL concentrated HNO3 2. Summary of method (sp gr 1.41) and dilute to 1000 mL with demin­ Cadmium is determined by atomic absorption eralized water. spectrometry following chelation with am­ 5.3 Cadmium standard solution II, 1.00 monium pyrrolidine dithiocarbamate (APDC) mL= 0.50 /*g Cd: Dilute 5.0 mL cadmium stand­ and extraction with methyl isobutyl ketone ard solution I and 1 mL concentrated HNO3 (sp (MIBK). The extract is aspirated into the air- gr 1,41) to 1,000 mL with demineralized water. acetylene flame of the spectrometer. 5.4 Cadmium standard solution III, 1.00 mL—0.05 /ig Cd: Immediately before use, dilute 3. Interferences 10.0 mL cadmium standard solution II to 100.0 Concentrations of iron greater than 25,000 mL with acidified water. This standard is used /tg/L interfere by depressing the cadmium ab­ to prepare working standards at time of sorption. analysis. 5.5 Citric odd-sodium citrate buffer solution: 4. Apparatus Dissolve 126 g citric acid monohydrate and 44 4.1 Atomic absorption spectrometer g sodium citrate dihydrate in demineralized equipped with electronic digital readout and water and dilute to 1 L with demineralized automatic zero and concentration controls. water. See NOTE 3 before preparation. 4.2 Refer to the manufacturer's manual to 5.6 Methyl isobutyl ketone (MIBK).

125 126 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.7 Potassium hydroxide, lOAf: Dissolve 56 analyzed and check calibration at reasonable g KOH in demineralized water, cool, and dilute intervals. to 100 mL. 5.8 Potassium hydroxide solution, 2.5M: 7. Calculations Dissolve 14 g KOH in demineralized water and 7.1 Determine the micrograms per liter of dilute to 100 mL (NOTE 1). dissolved or total recoverable cadmium in each NOTE 1. Alternately, a 2.5Af NH4OH solution sample from the digital display or printer while may be used. Add 167 mL concentrated aspirating each sample. Dilute those samples NH4OH (sp gr 0.90) to 600 mL demineralized containing concentrations of cadmium that ex­ water. Cool and dilute to 1 L. ceed the working range of the method; repeat 5.9 Water, acidified: Add 1.5 mL concen­ the chelation-extraction and multiply by the trated HNO3 (sp gr 1.41) to 1 L of deminer­ proper dilution factors. alized water. 7.2 To determine the micrograms per liter of suspended recoverable cadmium, subtract dis- 6. Procedure solved-cadmium concentration from total- 6.1 Clean all glassware used in this deter­ recoverable-cadmium concentration. mination with warm, dilute HNO3 (1+9) and rinse with demineralized water immediately 8. Report before use. Report cadmium, dissolved (01025), total- 6.2 Pipet a volume of sample solution con­ recoverable (01027), and suspended-recoverable taining less than 2.5 /*g Cd (100 mL max) into (01026), concentrations as follows: less than 10 a 200-mL volumetric flask, and adjust the pg/L, nearest microgram per liter, 10 pig/L and volume to approx 100 mL. above, two significant figures. 6.3 Prepare a blank of acidified water and sufficient standards, and adjust the volume 9. Precision of each to approx 100 mL with acidified 9.1 Precision for dissolved cadmium for 22 water. samples within the range of 2 to 17 pglL may 6.4 With a pH meter, adjust the pH of each be expressed as follows: solution to 2.7 (NOTES 2 and 3) with 2.5M KOH. Shake for 3 min. ST=0.213X- 0.111 NOTE 2. For water-suspended sediment sam­ ples which have been digested, add 1 to 2 mL where lOAf KOH or concentrated NH4OH (sp gr 0.90) ST= overall precision, micrograms per liter, before pH adjustment. and NOTE 3. If an automated titration system is X— concentration of cadmium, micrograms used to adjust the pH, add 2.5 mL citric acid- per liter. sodium citrate buffer solution prior to pH The correlation coefficient is 0.6914. adjustment. This will prevent over-shooting the 9.2 Precision for dissolved cadmium for four end point in poorly buffered samples. of the 22 samples expressed in terms of the per­ 6.5 Add 2.5 mL APDC solution and mix. cent relative standard deviation is as follows: 6.6 Add 10.0 mL MIBK and shake vigorous­ ly for 3 min. Number of Mean Relative standard deviation 6.7 Allow the layers to separate and add laboratories frO/U _____(percent)_____ demineralized water until the ketone layer is 6 2.0 32 completely in the neck of the flask. 11 4.6 24 6 10.2 17 6.8 Aspirate the ketone layer within 1 h. 12 17.2 34 Aspirate the ketone layer of the blank to set the automatic zero control. Use the automatic con­ 9.3 It is estimated that the percent relative centration control to set the concentrations of standard deviation for total recoverable and standards. Use at least six standards. Calibrate suspended recoverable cadmium will be greater the instrument each time a set of samples is than that reported for dissolved cadmium. Cadmium, atomic absorption spectrometric, direct

Parameters and Codes: Cadmium, dissolved, 1-1135-85 fcg/L as Cd): 01025 Cadmium, total recoverable, 1-3135-85 fcig/L as Cd): 01027 Cadmium, suspended recoverable, 1-7135-85 (jig/L as Cd): 01026 Cadmium, recoverable-from-bottom-material, 1-5135-85 (j*g/g as Cd): 01028

1. Application chromium (10,000 ^g/L each) do not interfere. 1.1 This method may be used to analyze Greater concentrations of each constituent were water and water-suspended sediment contain­ not investigated. ing at least 10 ftg/L of cadmium. Sample solu­ 3.2 Calcium at concentrations greater than tions containing more than 250 /ig/L need either 1,000 mg/L suppresses the cadmium absorp­ to be diluted or to be read on a less expanded tion. At 2,000 mg per liter of calcium, the sup­ scale. Sample solutions containing less than 10 pression is approximately 19 percent. fig/L need to be analyzed by the atomic absorp­ tion spectrometric chelation-extraction method, 4. Apparatus providing that the interference limits discussed 4.1 Atomic absorption spectrometer in that method are not exceeded. equipped with electronic digital readout and 1.2 Suspended recoverable cadmium is automatic zero and concentration controls. calculated by subtracting dissolved cadmium 4.2 Refer to the manufacturer's manual to from total recoverable cadmium. optimize instrument for the following: 1.3 This method may be used to analyze bot­ Grating T——————— Ultraviolet tom material containing at least 1 jig/g of Wavelength ————— 228.8 nm cadmium. Source (hollow-cathode 1.4 Total recoverable cadmium in water- lamp) ———————— Cadmium suspended sediment needs to undergo prelim­ Oxidant -——————— Air inary digestion-solubilization by method Fuel —————————— Acetylene 1-3485, and recoverable cadmium in bottom Type of flame ———— Oxidizing material needs to undergo preliminary diges­ 4.3 The Perkin-Elmer, flathead, single-slot tion-solubilization by method 1-5485 before be­ burner allows a working range of 10 to 250 /tg/L. ing determined* Different burners may be used according to manufacturers' instructions. 2. Summary of method Cadmium is determined by atomic absorption 5. Reagents spectrometry by direct aspiration of the sam­ 5.1 Cadmium standard solution 1, 1.00 mL= ple into an air-acetylene flame without precon- 100 fig Cd: Dissolve 0.1000 g Cd splatters in a centration or pretreatment of the sample. minimun of dilute HNO3. Heat to increase rate of dissolution. Add 10 mL concentrated HNO3 3. Interferences (sp gr 1.41) and dilute to 1,000 mL with demin- 3.1 Individual concentrations of sodium eralized water. (9,000 mg/L), potassium (9,000 mg/L)v magnes­ 5.2 Cadmium standard solution II, 1.00 ium (4,500 mg/L), sulfate (9,000 mg/L), chloride xnL= 1.0 /ig Cd: Dilute 10.0 mL cadmium stand­ (9,000 mg/L), nitrate (100 mg/L), iron (4X106 ard solution I and 1 mL concentrated HNO3 (sp jig/L), and cobalt, nickel, copper, zinc, lead, and gr 1.41) to 1,000 mL with demineralized water. 127 128 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Cadmium working standards: Prepare a (01026), concentrations as follows: less than series of at least six working standards contain­ 1,000 /*g/L, nearest 10 pglL; 1,000 pg/L and ing from 10 to 250 jtg/L of cadmium by appro­ above, two significant figures. priate dilution of cadmium standard solutions 8.2 Report cadmium, recoverable-from- I and II with acidified water. Prepare fresh daily. bottom-material (01028), concentrations as 5.4 Water, acidified: Add 1.5 mL concen­ follows: less than 10 jig/g, nearest microgram trated HNO3 (sp gr 1.41) to a liter of demineral- per gram; 10 j*g/g and above, two significant ized water. figures.

6. Procedure 9. Precision Aspirate the blank (acidified water) to set the 9.1 The standard deviation for dissolved cad­ automatic zero control. Use the automatic con­ mium within the range of 2.8 to 18.4 /ig/L for centration control to set the concentrations of 21 samples was found to be independent of standards. Use at least six standards. Calibrate concentration. The 95-percent confidence inter­ the instrument each time a set of samples is val for the average standard deviation of 3.57 analyzed and check calibration at reasonable in­ /*g/L ranged from 3.24 to 3.95 j*g/L. tervals. 9.2 Precision for dissolved cadmium for five of the 21 samples expressed in terms of the 7. Calculations percent relative standard deviation is as 7.1 Determine the micrograms per liter of follows: dissolved or total recoverable cadmium in each sample from the digital display or printer while Number of Mean Relative standard deviation laboratories _____(percent)______aspirating each sample. Dilute those samples containing cadmium concentrations that exceed 12 2.8 124 17 4.8 50 the working range of the method and multiply 15 10.7 19 by the proper dilution factors. 15 15.7 24 7.2 Tb determine micrograms per liter sus­ 5 18.4 71 pended recoverable cadmium, subtract dissolved- cadmium concentration from total-recoverable- 9.3 It is estimated that the percent relative cadmium concentration. standard deviation for total recoverable and 7.3 Tb determine micrograms per gram of suspended recoverable cadmium and for recov­ cadmium in bottom-material samples, first erable cadmium from bottom material will be determine the micrograms per liter of cadmium greater than that reported for dissolved in each sample as in paragraph 7.1; then cadmium. 9.4 Precision for total recoverable cadmium mL of original digest expressed in terms of the percent relative stand­ CdX ard deviation for two water-suspended sediment 1^000 Cd mixtures is as follows: wt of sample (g)

Number of Mean Relative standard deviation 8. Report laboratories ____(percent) ____ 8.1 Report cadmium, dissolved (01025), total- 13 5.4 43 recoverable (01027), and suspended-recoverable 15.8 25 Cadmium, atomic absorption spectrometric, graphite furnace

Parameter and Code: Cadmium, dissolved, 1-1137-85 (/*g/L as Cd): 01025

1. Application form reduces the effects of many interferences. 1.1 This method may be used to determine Calcium (25 mg/L), magnesium (8 mg/L), sodium ' cadmium in low ionic-strength water and pre­ (20 mg/L), sulfate (34 mg/L), and chloride (25 cipitation. With deuterium background correc­ mg/L) do not interfere. Greater concentrations tion and a 20-jiL sample, the method is of these constituents were not investigated. applicable in the range from 0.02 to 1.0 jtg/L. 3.2 Precipitation samples usually contain With Zeeman background correction and a very low concentrations of cadmium. Special 20-/iL sample, the method is applicable in the precautionary measures must be employed dur­ range from 0.1 to 3.0 Mg/L. Sample solutions ing both sample collection and laboratory that contain cadmium concentrations exceeding determination to prevent contribution from the upper limits must be diluted or preferably contamination. be analyzed by the atomic absorption spec­ trometric direct or chelation- extraction method 4. Apparatus or by the atomic emission spectrometric ICP 4.1 Atomic absorption spectrometer, for use method. at 228.8 nm and equipped with background cor­ 1.2 The analytical range and detection limits rection, digital integrator to quantitate peak can be increased or possibly decreased by vary­ areas, graphite furnace with temperature pro­ ing the volume of sample injected or the instru­ grammer, and automatic sample injector. The mental settings. Purification of reagents and programmer must have high-temperature ramp­ use of ASTM Type 1 water (Method D-1193, ing and stopped-flow capabilities. American Society for Testing and Materials, 4.1.1 Refer to the manufacturer's manual to 1984) may result in lower detection limits. optimize instrumental performance. The analyt­ ical ranges reported in paragraph 1.1 are for a 2. Summary of method 20-pL sample with 5 /xL of matrix modifier Cadmium is determined by atomic absorption (NOTE 1). spectrometry in conjunction with a graphite fur­ NOTE 1. A 20-/iL sample generally requires 30 nace containing a graphite platform (Hinder- s to dry. Samples that have a complex matrix berger and others, 1981). A sample is placed on may require a longer drying and charring time. the graphite platform and a matrix modifier is 4.1.2 Graphite furnace, capable of reaching added. The sample is then evaporated to dry- temperatures sufficient to atomize the element ness, charred, and atomized using high-temper­ of interest. Warning: dial settings frequently ature ramping. The absorption signal generated are inaccurate and newly conditioned furnaces during atomization is recorded and compared require temperature calibration. with standards. 4.1.3 Graphite tubes and platforms. Pyrolyt- ically coated graphite tubes and solid pyrolytic 3. Interferences graphite platforms are recommended. 3.1 Interferences in low ionic-strength sam­ 4.2 Lab ware. Many trace metals at very ples, such as precipitation, normally are quite low concentrations have been found to sorb low. In addition, the use of the graphite plat­ very rapidly to glassware. To preclude this, 129 130 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS fluorinated ethylene propylene (FEP) or Teflon than 0.005 absorbance-seconds, purify the solu­ labware may be used. Alternately, glassware, tion by chelation with ammonium pyrrolidine particularly flasks and pipets, may be treated dithiocarbamate (APDC) and extraction with with silicone anti-wetting agent such as Surfacil methyl isobutyl ketone (MIBK) (NOTE 3). (Pierce Chemical Co., Rockford, IL, 61105) ac­ Analyze 20 /*L of the purified solution. Repeat cording to the manufacturer's instructions. extractions until the cadmium level is reduced Autosampler cups must be checked for contam­ to the acceptable level. DO NOT ADD ACID ination. Lancer (1831 Olive St., St. Louis, MO, TO THE PURIFIED MATRIX MODIFIER 63103) polystyrene disposable cups have been SOLUTION. found to be satisfactory after acid rinsing. NOTE 3. To purify matrix modifier solution, Alternately, reuseable Teflon or FEP cups may pour the solution into a Teflon or FEP con­ be used. tainer. Add 0.25g APDC for each liter of solu­ 4.3 Argon, standard, welder's grade, com­ tion. While stirring, adjust the solution to pH mercially available. Nitrogen may also be 2.9 by dropwise addition of concentrated HNO3 used if recommended by the instrument (sp gr 1.41). Transfer portions of the solution manufacturer. to a separatory funnel, add 100 mL MIBK/liter of solution, and shake vigorously for at least 5 5. Reagents min. Frequently, vent the funnel in a hood. Col­ 5.1 Cadmium standard solution I, 1.00 mL= lect the extracted solution in the FEP container. 1,000 /zg Cd: Dissolve 1.0000 g Cd splatters in Repeat the extraction with 50 mL MIBK/liter a minimum of dilute HNO3. Heat to increase of solution. Because MIBK can dissolve some rate of dissolution. Add 10 mL high-purity plastic autosampler cups, boil the solution for concentrated HNO3 (sp gr 1.41), Ultrex or at least 10 min in a silicone-treated or acid- equivalent, and dilute to 1,000 mL with Type rinsed container covered with a watchglass to 1 water. remove MIBK. 5.2 Cadmium standard solution II, 1.00 5.6 Nitric acid, concentrated, high-purity, mL= 10.0 /ig Cd: Dilute 10.0 mL cadmium (sp gr 1.41): J. T. Baker "Ultrex" brand HNO3 standard solution I to 1,000 mL (NOTE 2). has been found to be adequately pure; however, NOTE 2. Use acidified Type 1 water (paragraph each lot must be checked for contamination. 5.7) to make dilutions. All standards must be Analyze acidified Type 1 water for cadmium. stored in sealed Teflon or FEP containers. Each Add an additional 1.5 mL of concentrated container must be rinsed twice with a small HNO3/liter of water, and repeat analysis. The volume of standard before being filled. Stand­ integrated signal should not increase by more ards stored for 6 months in FEP containers than 0.001 absorbance-seconds. yielded values equal to those of freshly prepared 5.7 Water, acidified, Type 1: Add 1.5 mL standards. high-purity, concentrated HNO3 (sp gr 1.41) to 5.3 Cadmium standard solution III, 1.00 each liter of water. mL= 0.100 /ig Cd: Dilute 10.0 mL cadmium 5.8 Water, Type 1 standard solution II to 1,000 mL. This stand­ ard is used to prepare working standards serial­ 6. Procedure ly at time of analysis. 6.1 Systematically clean and rinse work 5.4 Cadmium standard solution IV, 1.00 areas with deionized water on a regular sched­ mL= 0.001 Mg Cd: Dilute 10.0 mL cadmium ule. Use a laminar flow hood or a "clean room" standard solution III to 1,000 mL. This stand­ environment during sample transfers. Ideally, ard also is used to prepare working standards the autosampler and the graphite furnace serially at time of analysis. should be in a clean environment. 5.5 Matrix modifier solution, 40g 6.2 Soak autosampler cups at least over­ NH4H2PO4/L: Add 40.0 g NH4H2PO4 to 950 night in a 1+1 solution of Type 1 water and mL Type 1 water, mix, and dilute to 1,000 mL. high-purity nitric acid. Analyze 20 j*L of matrix modifier for cadmium 6.3 Rinse the sample cups twice with sam­ contamination. If the cadmium reading is more ple before filling. Place cups in sample tray and METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 131

Relative standard cover. Adjust sampler so that only the injection Number of Mean Standard deviation deviation tip contacts the sample. replicates (MO/L) to/u (percent) 6.4 In sequence, inject 20-piL aliquots of 4 0.50 0.115 23 blank and working standards plus 5 /*L of 12 1.60 .060 3.8 modifier each and analyze. Analyze the blank 6 2.10 .089 4.2 and working standards twice. Construct the 14 3.14 .074 2.4 analytical curve from the integrated peak areas 9.3 The precision and bias for the Zeeman (absorbance-seconds). Generally, the curve background correction were tested on deionized should be linear to a peak-absorbance (peak- water and tap water (specific conductance 280 height) value of 0.40 absorbance units. /iS/cm). A known amount of cadmium was 6.5 Similarly, inject and analyze the samples added to each sample, and single-operator preci­ twice. Every tenth sample cup should contain sion and bias for six replicates are as follows: either a standard or a reference material. Relative 6.6 Restandardize as required. Minor changes Amount Amount Standard standard of values for known samples usually indicate added found deviation deviation Recovery deterioration of the furnace tube, contact rings, (percent) (percent) and/or platform. A major variation usually indi­ Deionized water cates either autosampler malfunction or residue 2.6 2.25 0.05 2.2 87 buildup from a complex matrix in a previous 3.25 2.77 .05 1.8 85 sample. 5.0 4.53 .15 3.3 91 5.2 4.42 .17 3.8 85 6.5 5.63 .08 1.4 87 7. Calculations Determine the micrograms per liter of cad­ Tap water mium in each sample from the digital display 2.6 2.05 .08 3.9 79 or printer output. Dilute those samples contain­ 3.25 2.55 .41 7.9 80 ing concentrations of cadmium that exceed the 5.00 4.52 .12 2.7 90 5.2 3.90 .15 3.8 75 working range of the method; repeat the analy­ 6.5 5.22 .41 7.9 80 sis, and multiply by the proper dilution factors. 9.4 The precision and bias for the deuterium 8. Report background method were tested on deionized Report cadmium, dissolved (01025), concen­ water and tap water (specific conductance 280 trations as follows: less than 1.0 jug/L, nearest /iS/cm). A known amount of cadmium was 0.01 /ig/L for deuterium background correction added to each sample, and single-operator preci­ or nearest 0.1 /ig/L for Zeeman background cor­ sion and bias for six replicates are as follows: rection; 1.0 jig/L and above, two significant figures for both deuterium background correc­ Relative Amount Amount Standard standard tion and Zeeman background correction. added found deviation deviation Recovery _____(fig/L) _____ QiQ/L) ____ (percent) (percent) 9. Precision Deionized water 9.1 Analysis of five samples six times each 2.6 2.55 0.31 12 98 by a single operator using deuterium back­ 3.25 2.72 .15 5.5 84 5.0 4.70 .30 6.4 94 ground correction is as follows: 5.2 4.97 .44 8.9 96 6.5 5.83 .33 5.6 90 Mean Standard deviation Relative standard deviation (M9/L) _____(percent)______Tap water 0.030 0.004 6.9 .106 .004 4.0 2.6 3.03 1.0 33 117 .249 .009 3.4 3.25 2.83 .25 8.8 87 .499 .010 2.0 5.0 4.53 .27 6.0 91 1.005 .013 1.3 5.2 4.23 .21 5.0 81 6.5 5.48 .15 2.7 84 9.2 Analysis of four samples by a single operator using Zeeman background correction 9.5 Interlaboratory precision for dissolved is as follows: cadmium for 16 samples within the range of 132 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 0.62 to 16.2 Aig/L, without regard to type of Cooksey, M., and Barnett, W. B., 1979, Matrix modification background correction and use of matrix modi­ and the method of additions in flameless atomic absorp­ tion: Atomic Absorption Newsletter, v. 18, p. 101-5. fiers, if any, may be expressed as follows: Fernandez, F. J., Beatty, M. M., and Barnett, W. B., 1981, Use of the L'vov platform for furnace atomic absorp­ ST= 0.282X + 0.022 tion applications: Atomic Spectroscopy, v. 2, p. 16-21. Hinderberger, £. J., Kaiser, M. L., and Koirtyohann, S. R., where 1981, Furnace atomic absorption analysis of biological ST= overall precision, micrograms per liter, samples using the L'vov platform and matrix modific­ ation: Atomic Spectroscopy, v. 2, p. 1-11. and Manning, D. C., and Slavin, W., 1983, The determination X= concentration of cadmium, micrograms of trace elements in natural waters using the stabilized per liter. temperature platform furnace: Applied Spectroscopy, The correlation coefficient is 0.9157. v. 37, p. 1-11. Ottaway, J. M., 1982, A revolutionary development in graphite furnace atomic absorption: Atomic Spectro­ References scopy, v. 3, p. 89-92. Slavin, W., Carnrick, G. R., and Manning, D. C., 1982, American Society for Testing and Materials, 1984, Annual Magnesium nitrate as a matrix modifier hi the stabil­ book of ASTM standards, section 11, water: Philadel­ ized temperature platform furnace: Analytical Chem­ phia, v. 11.01, p. 39-41. istry, v, 54, p. 621-4. Cadmium, atomic emission spectrometric, ICP

Parameter and Code: Cadmium, dissolved, 1-1472-85 0*g/L as Cd): 01025

2. Summary of method metric method utilizing an induction-coupled Cadmium is determined simultaneously argon plasma as an excitation source. See with several other constituents on a single method 1-1472, metals, atomic emission spec­ sample by a direct-reading emission spectro­ trometric, ICP. 133

Cadmium, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Cadmium, total, 1-5474-85 (mg/kg as Cd): none assigned

2. Summary of method hotplate at 200 °C. Cadmium is determined on A sediment sample is dried, ground, and the resulting solution by atomic absorption homogenized. The sample is digested with a spectrometry. See method 1-5474, metals, ma­ combination of nitric, hydrofluoric, and per­ jor and minor, total-in-sediment, atomic absorp­ chloric acids in a Teflon beaker heated on a tion spectrometric, direct. 135

Calcium, atomic absorption spectrometric, direct

Parameters and Codes: Calcium, dissolved, 1-1152-85 (mg/L as Ca): 00915 Calcium, total recoverable, 1-3152-85 (mg/L as Ca): none assigned Calcium, suspended recoverable, 1-7152-85 (mg/L as Ca): 81357 Calcium, recoverable-from-bottom-material, dry wt 1-5152-85 (mg/kg as Ca): 00917

1. Application recoverable calcium in bottom material needs 1.1 This method may be used to analyze at­ to undergo preliminary digestion-solubilization mospheric precipitation, water, brines, and by method 1-5485 before being determined. water-suspended sediment. 1.2 Two analytical ranges for calcium are in­ 2. Summary of method cluded: from 0.01 to 5.0 mg/L and from 1.0 to 2.1 Calcium is determined by atomic absorp­ 60 mg/L. Sample solutions containing calcium tion spectrometry (Fishman and Downs, 1966). concentrations greater than 60 mg/L need to be Lanthanum chloride is added to mask inter­ diluted. ferences. 1.3 Suspended recoverable calcium is calcu­ 2.2 This procedure may be automated by the lated by subtracting dissolved calcium from addition of a sampler, a proportioning pump, total recoverable calcium. and a strip-chart recorder or printer or both 1.4 This method may be used to analyze bot­ (fig. 19). tom material containing at least 10 mg/kg of calcium. 3. Interferences 1.5 Total recoverable calcium in water-sus­ 3.1 Phosphate, sulfate, and aluminum inter­ pended sediment needs to undergo preliminary fere but are masked by the addition of lanthan­ digestion-solubilization by method 1-3485, and um. Silica also reportedly interferes. Because

lirator Water k Long O.OSlin mixing coil 2.52 mL/min > O.OSlin Sample i * i 2.52 mL/min Air , O -E>3- O.OSlin Sampler t 2.52 mL/min PS- 3 Lanthanum O.OSSin chloride 0.42 mL/min ste Water To samplei' 4 O.OSlin 2.52 mL/min wash rece ptaclt!

Figure 19.—Calcium manifold

137 138 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS low calcium values result if the pH of the sam­ of standard. Similarly, prepare a demineralized ple is above 7, standards are prepared in hydro­ water blank. chloric acid solution and samples are preserved 5.3 Lanthanum chloride solution, 87 g/L: in the field with use of nitric acid solution. Mix 29 g of La2O3 with a few milliliters of Concentrations of magnesium greater than demineralized water to form a slurry. Slowly 1,000 mg/L also cause low calcium values. add 250 mL concentrated HC1 (sp gr 1.19) while 3.2 Nitrate interferes, but in the presence of stirring (reaction may be violent) to dissolve the lanthanum chloride-hydrochloric acid solution La2O3. Dilute to 500 mL with demineralized at least 2,000 mg/L can be tolerated. The addi­ water. tion of nitric acid to the sample causes no prob­ lem in the following procedure. 6. Procedure 6.1 Add 1.0 mL of LaCl3 solution per 10.0 4. Apparatus mL of sample solution. 4.1 Atomic absorption spectrometer 6.2 Aspirate the blank to set the automatic equipped with electronic digital readout and zero control. Use the automatic concentration automatic zero and concentration controls. control to set the concentrations of standards. 4.2 Refer to the manufacturer's manual to Use at least six standards. Calibrate the instru­ optimize instrument for the following: ment each time a set of samples is analzyed and Grating ———————— Visible check calibration at reasonable intervals. Wavelength ————— 422.7 nm Source (hollow-cathode 7. Calculations lamp) ———————— Calcium 7.1 Determine the milligrams per liter of dis­ Oxidant ———————— Air solved or total recoverable calcium in each sam­ Fuel —————————— Acetylene ple from the digital display or printer while Type of flame ———— Slightly aspirating each sample. Dilute those samples reducing containing calcium concentrations that exceed 4.3 The 50-mm (2-in.), flathead burner allows the working range of the method and multiply a working range of 0.01 to 5.0 mg/L. This by the proper dilution factors. burner, rotated 90°, allows a working range of 7.2 To determine milligrams per liter of 1.0 to 60 mg/L. suspended recoverable calcium, subtract dis- 4.4 Different burners may be used according solved-calcium concentration from total-re­ to manufacturers' instructions. A nitrous ox­ coverable-calcium concentration. ide-acetylene flame will provide two to five 7.3 To determine milligrams per kilogram of times greater analytical sensitivity and freedom calcium in bottom-material samples, first deter­ from chemical interferences; however, sodium mine the milligrams per liter of calcium in each or potassium chloride must be added to control sample as in paragraph 7.1; then ionization of calcium. mL of original digest mg/L CaX 1000 "" Ca (mg/kg)=- 5. Reagents wt of sample (kg) 5.1 Calcium standard solution, 1.00 mL= 0.500 mg Ca: Suspend 1.250 g CaCO3, dried at 8. Report 180°C for 1 h before weighing, in demineralized 8.1 Report calcium, dissolved (00915), total- water and dissolve cautiously with a minimum recoverable (none assigned), and suspended- of dilute HC1. Dilute to 1,000 mL with demin­ recoverable (81357), concentrations as follows: eralized water. less than 1.0 mg/L, two decimals; 1.0 to 10 5.2 Calcium working standards: Prepare mg/L, one decimal; 10 mg/L and above, two sig­ at least six working standards containing nificant figures. either from 0.01 to 5.0 mg/L or from 1.0 to 8.2 Report calcium, recoverable-from-bot- 60 mg/L of calcium by diluting the calcium tom-material (00917), concentrations as follows: standard solution. To each working standard less than 1,000 mg/kg, nearest 10 mg/kg; 1,000 add 1.0 mL of LaCl3 solution for each 10 mL mg/kg and above, two significant figures. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 139 9. Precision 9.3 Precision for dissolved calcium within 9.1 Precision for dissolved calcium for 37 the range of 0.05 to 5.0 mg/L in terms of the per­ samples within the range of 0.84 to 184 mg/L cent relative standard deviation by a single may be expressed as follows: operator is as follows:

Number of Mean Relative standard deviation ST= 0.087X- 0.249 replicates (mg/L) _____(percent)_____ 8 0.052 40.4 where 8 1.02 5.9 8 1.85 10.3 ST= overall precision, milligrams per liter, 8 5.05 1.0 and 9.4 It is estimated that the percent relative X= concentration of calcium, milligrams per standard deviation for total recoverable and liter. suspended recoverable calcium and for recover­ The correlation coefficient is 0.8632. able calcium from bottom material will be 9.2 Precision for dissolved calcium for five greater than that reported for dissolved of the 37 samples expressed in terms of the per­ calcium. cent relative standard deviation is as follows:

Number of Mean Relative standard deviation laboratories (mg/L) _____(percent)____ Reference 20 0.84 24 14 10.7 6 Fishman, M. J., and Downs, 3. CM 1966, Methods for 45 50.1 8 analysis of selected metals in water by atomic absorp­ 23 110 8 tion: U.S. Geological Survey Water-Supply Paper 36 184 10 1540-C, p. C26-C28.

Calcium, atomic absorption spectrometric, direct-EPA

Parameter and Code: Calcium, total recoverable, 1-3153-85 (mg/L as Ca): 00916

1. Application at least 2,000 mg/L can be tolerated. The addi­ 1.1 This method may be used to analyze tion of nitric acid to the sample as a preserv­ water-suspended sediment. Sample solutions ative at the time of collection causes no problem containing from 0.1 to 60 mg/L of calcium may in the following procedure. Samples should be be analyzed without dilution; whereas, those evaporated just to dryness following nitric acid containing more than 60 mg/L need to be digestion to avoid any possible nitrate in­ diluted. terference. 1.2 For ambient water, analysis may be made on a measured portion of the acidified 4. Apparatus water-suspended sediment sample. 4.1 Atomic absorption spectrometer 1.3 For all other waters, including domestic equipped with electronic digital readout and and industrial effluent, the atomic absorption automatic zero and concentration controls. procedure must be preceded by a digestion- 4.2 Refer to the manufacturer's manual to solubilization as specified below. In cases where optimize instrument for the following: the analyst is uncertain about the type of sam­ Grating ———————— Visible ple, the digestion-solubilization procedure must Wavelength ————— 422.7 nm be used. Source (hollow-cathode lamp) ———————— Calcium 2. Summary of method Oxidant ———————— Air 2.1 Calcium is determined by atomic absorp­ Fuel —————————— Acetylene tion spectrometry (Fishman and Downs, 1966). Type of flame ———— Slightly reducing Lanthanum chloride is added to mask inter­ 4.3 Different burners may be used according ferences. to manufacturers' instructions. A nitrous ox­ 2.2 Effluent samples must undergo a pre­ ide-acetylene flame provides 2 to 5 times greater liminary nitric acid digestion followed by a sensitivity and freedom from chemical inter­ hydrochloric acid solubilization. ferences; however, sodium or potassium chloride must be added to control ionization of calcium. 3. Interferences 3.1 Phosphate, sulfate, and aluminum in­ 5. Reagents terfere but are masked by the addition of 5.1 Calcium standard solution, 1.00 mL= lanthanum. Silica reportedly also interferes. 0.500 mg Ca: Suspend 1.250 g CaCO3, dried at Because low calcium values result if the pH of 180°C for 1 h before weighing, in demineralized the sample is above 7, standards are prepared water and dissolve cautiously with a minimum in hydrochloric acid solution and samples are of dilute HCL Dilute to 1,000 mL with demin­ preserved in the field with use of nitric acid solu­ eralized water. tion. Concentrations of magnesium greater than 5.2 Calcium working standards: Prepare a 1,000 mg/L also cause low calcium values. series of at least six working standards contain­ 3.2 Nitrate interferes, but in the presence of ing from 0.1 to 60 mg/L of calcium by dilution lanthanum chloride-hydrochloric acid solution, of calcium standard solution. To each working 141 142 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS standard add 1.0 mL of LaCl3 solution for each filter with hot, 0.3M HC1. Dilute to the original 10 mL of standard. volume with demineralized water. 5.3 Hydrochloric acid, 6M: Dilute 500 mL 6.8 Add 1.0 mL lanthanum chloride solution concentrated HC1 (sp gr 1.19) to 1 L with per 10.0 mL of sample. demineralized water. 6.9 Aspirate the blank to set the automatic 5.4 Hydrochloric acid, 0.3M: Dilute 25 mL zero control. Use the automatic concentration concentrated HC1 (sp gr 1.19) to 1 L with demin­ control to set the concentrations of standards. eralized water. Use at least six standards. Calibrate the instru­ 5.5 Lanthanum chloride solution, 87 g/L: ment each time a set of samples is analyzed and Mix 29 g La2O3 with a few milliliters of demin­ check calibration at reasonable intervals. eralized water to form a slurry. Slowly add 250 mL concentrated HC1 (sp gr 1.19) while stirring 7. Calculations (reaction may be violent) to dissolve the La2O3. Determine the milligrams per liter of total Dilute to 500 mL with demineralized water. recoverable calcium in each sample from the 5.6 Nitric acid, concentrated (sp gr 1.41). digital display or printer while aspirating each sample. Dilute those samples containing 6. Procedure calcium concentrations that exceed the working 6.1 Transfer the entire sample to a beaker. range of the method and multiply by the proper 6.2 Rinse the sample bottle with 3 mL con­ dilution factors. centrated HNO3 for each 100 mL of sample and add to the beaker. Prepare a blank using 3 mL 8. Report concentrated HNO3 per 100 mL demineralized Report calcium, total-recoverable (00916), water. concentrations as follows: less than 10 mg/L, 6.3 Evaporate samples and blank to dryness one decimal; 10 mg/L and above, two significant on a hotplate, making sure the samples do not figures. boil. 6.4 Cool and add an additional 3 mL concen­ 9. Precision trated HNO3 to the beaker. Cover with a It is estimated that the percent relative stand­ watchglass, return to the hotplate, and gently ard deviation for total recoverable calcium over reflux the sample. the range of the method will be greater than 8 6.5 Continue heating, adding additional acid percent. as necessary, until the digestion is complete (in­ dicated by a light-colored residue). Evaporate References just to dryness. 6.6 Add 6 mL 6M HC1 solution per 100 mL Fishman, M. J., and Downs, S. C., 1966, Methods for of original sample and warm the beaker to dis­ analysis of selected metals in water by atomic absorp­ solve the residue. tion: U.S. Geological Survey Water-Supply Paper 1540-C, p. C26-C28. 6.7 Wash the watchglass and beaker with U.S. Environmental Protection Agency, 1979, Methods for demineralized water and filter the sample chemical analysis of water and wastes: Cincinnati, U.S. (Whatman No. 41 or equivalent), rinsing the Environmental Protection Agency, p. 215.1-1. Calcium, atomic emission spectrometric, ICP

Parameter and Code: Calcium, dissolved, 1-1472-85 (mg/L as Ca): 00915

2. Summary of method method utilizing an induction-coupled argon Calcium is determined simultaneously plasma as an excitation source. See method with several other constituents on a single sam­ 1-1472, metals, atomic emission spectrometric, ple by a direct-reading emission spectrometric ICP. 143

Calcium, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Calcium, total, 1-5473-85 (mg/kg as Ca): none assigned Calcium, total, 1-5474-85 (mg/kg as Ca): none assigned

2. Summary of method See method 1-5473, metals, major, total in 2.1 A sediment sample is dried, ground, sediment, atomic absorption spectrometric, and homogenized. The sample is then treated direct. and analyzed by one of the following tech­ 2.1.2 The sample is digested with a combina­ niques. tion of nitric, hydrofluoric, and perchloric acids 2.1.1 The sample is fused with a mixture of in a Teflon beaker heated on a hotplate at lithium metaborate and lithium tetraborate in 200 °C. Calcium is determined on the resulting a graphite crucible in a muffle furnace at solution by atomic absorption spectrometry. 1000 °C. The resulting bead is dissolved in acidi­ See method 1-5474, metals, major and minor, fied, boiling, demineralized water, and calcium is total-in-sediment, atomic absorption spectro­ determined by atomic absorption spectrometry. metric, direct. 145

Carbon dioxide, calculation

Parameter and Code: Carbon dioxide, dissolved, 1-1160-85 (mg/L as CO2): 00405

1. Application equations (1) and (3) and their corresponding This method may be applied to any sample equilibrium-constant expressions as follows: for which measured values of pH and bicar­ bonate ion are available. J5£9s! = 2.6X10-3 (5) 2. Summary of method [C02] 2.1 Carbon dioxide concentration is calcu­ lated from measured values of pH and bicar­ [H+1] [HCO;1] bonate ion. The pH is determined potentio- R = i——11__aj = l ? x 10_4 (6) metrically (method 1-1586) and the bicarbonate [HgCOg] ion by electrometric titration (method 1-1030). 2.2 Gaseous carbon dioxide hydrolyzes Multiply equations (5) and (6): slightly: CO2(aq) + H2O -* H2CO3 (1) = 4.4 X10-7 (7) IC02] The hydrolysis constant expression is: and solving for [CO2]:

(2) [co2] [C02] = (2) 4.4X10-7 The square brackets denote concentrations in moles per liter. This equation can then be used to determine Carbonic acid is a weak acid and dissociates the CO2 concentration when [HCO§1] and by steps: [H+ 1], or pH, of the sample have been deter­ mined. Equation (8) can be rearranged to HCOg 1 (3) simplify the calculation, since both CO2 and bicarbonate [HCO^1] concentrations are usually g1 * R+ 1 + C0§2 (4) expressed in units of milligrams per liter rather than of moles per liter, and hydrogen-ion con­ Only the two equilibria represented by equ­ centrations normally as pH units: ations (1) and (3), however, are usually of sig­ nificance in determining CO2 concentrations. mg CO2/L = 1.60X10<6-°-PH>Xmg HCOgVLO) When the pH of a water is sufficiently high to permit the existence of CO§2, the concentration For convenience in making the calculations, of free CO2 that can coexist is negligibly small. the values of 1.60X10<6-°-PH> may be tabulated for a range of pH values (table 7). The CO2 concentrations can, therefore, be cal­ 2.3 For additional information on the theory culated within experimental accuracy from of this method see De Martini (1938), Langelier 147 148 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Table 7.—Values of 1.60x10<6-°-PH) 7. Calculations 7.1 Calculate mg/L CO2 as follows: pH 1.60x10<6-°-PH> PH 1.60x10<6-°-PH» 6.0 1.60 7.6 0.040 mg/L CO2 = 1.60X10<6-°-PH>Xmg/L HCOg1 6.2 1.00 7.8 .025 6.4 .633 8.0 .016 6.6 .399 8.2 .010 7.2 The calculated values of the variable 6.8 .252 8.4 .006 1.60X10<6-°-PH> are shown in table 7. 7.0 .160 8.6 .004 7.2 .100 8.8 .003 7.4 .063 9.0 .002 8. Report Report carbon dioxide, dissolved, calculation (1936), Larson and Buswell (1942), and Moore (00405), concentrations as follows: less than 10 (1939). mg/L, one decimal; 10 mg/L and above, two sig­ nificant figures. 3. Interferences 3.1 The values of the constants ^nydr an^ 9. Precision KI vary with temperature and with both the Precision data are not available for this concentration and nature of the dissolved method. solutes. Therefore, the accuracy of the calcul­ ation depends on the reliability of values of References l^hydr and K± for a particular sample. For prac­ tical purposes and for most samples containing De Martini* F. E., 1938, Corrosion and the Langelier calcium less than SOO mg/L of solutes, a value for carbonate saturation index: American Water Works Association Journal v. 30, p. 85. (KhydrXKi> of 4.54X10-7 has been recom­ Langelier, W. FM 1936, The analytical control of anti- mended and was used in calculating the con­ corrosion water treatment: American Water Works stant factor of equation (9). Association Journal, v. 28 p. 1500. 3.2 Carbon dioxide is easily lost from solu­ Larson, T. E., and Buswell, A. N., 1942, Calcium carbonate tion, and precautions must be taken to prevent saturation and alkalinity interpretations: American Water Works Association Journal, v. 34, p. 1667. or minimize such losses when collecting the Moore, E. W., 1939, Graphic determination of carbon diox­ sample. The pH and bicarbonate must be deter­ ide and three forms of alkalinity: American Water mined in the field at the time of collection. Works Association Journal, v. 31, p. 51. Chloride, colorimetric, ferric thiocyanate Parameter and Code: Chloride, dissolved, 1-1187-85 (mg/L as Cl): 00940

1. Application 5. Reagents This method may be used to determine dis­ 5.1 Chloride standard solution /, 1.00 mL— solved chloride in water containing from 0.1 to 1.00 mg Cl"1: Dissolve 1.648 g primary stand­ 10 mg/L of chloride ion. It is particularly useful ard NaCl crystals, dried at 180 °C for 1 h, in for the analysis of low-dissolved- solids-content demineralized water and dilute to 1,000 mL. water when low chloride concentrations must be 5.2 Chloride standard solution II, 1.00 mL= determined accurately. 0.010 mg Cl"1: Dilute 5.0 mL chloride standard solution I to 500.0 mL with demineralized 2. Summary of method water. 2.1 Chloride is determined by measurement 5.3 Ferric ammonium sulfate solution, 22.8 of the color developed by the displacement of g/L: Dissolve 41.4 g FeNH4(SO4)2-12H2O in 570 the thiocyanate ion from mercuric thiocyanate mL concentrated HNO3 (sp gr 1.41) and dilute by chloride ion in the presence of ferric ion; an to 1 L with demineralized water. intensely colored ferric thiocyanate complex is 5.4 Mercuric thiocyanate solution, 3 g/L: formed: Dissolve 3 g Hg(SCN)2 in 1 L 95-percent ethanol (denatured alcohol formula No. 3A is 2C1'1 + Hg(SCN)2 also satisfactory). Stir for 1 h to saturate the solvent; allow undissolved thiocyanate to set­ HgCl2 + 2Fe(SCN)+2 tle, and then filter through a Pyrex-wool plug or a 0.45-/*m membrane filter. 2.2 The color is stable for at least 2 h and is proportional to the chloride-ion concentration. 6. Procedure The color has a maximum absorbance at 6.1 Pipet a volume of sample containing less 460 nm. than 0.250 mg of Cl'1 (25.0 mL max) into a 2.3 For additional information see ASTM 50-mL beaker and adjust the volume to 25*0 mL Method D 512-81, "Standard Methods of with demineralized water. Testing for Chloride Ion in Water" (American 6.2 Prepare a demineralized-water blank and Society for Testing and Materials, 1984). at least five standards containing from 0.0025 to 0.250 mg Cl'1, and adjust the volume of each 3. Interferences to 25.0 mL. Bromide, iodide, cyanide, thiosulfate, and 6.3 Add 2.0 mL FeNH4(SO4)2 solution and nitrite interfere. Color, depending upon its spec­ stir. The samples will be essentially colorless at tral absorbance, may interfere with the this point. photometric measurement. 6.4 Add 2.0 mL Hg(SCN)2 solution and stir. 6.5 After at least 10 min, but within 2 h, 4. Apparatus read the absorbance of each standard and 4.1 Spectrometer for use at 460 nm. sample against the blank at 460 nm, and, 4.2 Refer to manufacturer's manual to op­ when necessary, make corrections for water timize instrument. color. 149 150 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 7. Calculations 7.1 Determine the milligrams chloride from a plot of absorbances of standards containing where known amounts of Cl"1. S^overall precision, milligrams per liter, 7.2 Determine the chloride concentration in and milligrams per liter as follows: X=concentration of Cl"1, milligrams per liter. 1 000 9.2 Precision for one reference sample ex­ Cl-1 (mg/L)=——-———XmgCH pressed hi terms of the percent relative stand­ mL sample ard deviation is as follows: 8. Report Report chloride, dissolved (00940), concentra­ Number of Mean Relative standard deviation tions of less than 10 mg/L to the nearest 0.1 laboratories (mp/L) _____(percent)____ mg/L. 1.4 33

9. Precision Reference 9.1 Data published by the American Socie­ American Society for Testing and Materials, 1984, Annual ty for Testing and Materials (1984) indicate the book of ASTM standards, section 11, water: overall precision of the method to be Philadelphia, v. 11.01, p. 392-400. Chloride, colorimetric, ferric thiocyanate, automated-segmented flow Parameter and Code: Chloride, dissolved, 1-2187-85 (mg/L as Cl): 00940

1. Application 5. Reagents This method may be used to determine con­ 5.1 Chloride standard solution /, 1.00 mL= centrations of chloride in surface, domestic, and 0.50 mg Cl'1: Dissolve 0.8242 g primary stand­ industrial water in the range of 10 to 100 mg/L ard NaCl crystals, dried at 180° C for 1 h, in or 0.1 to 10.0 mg/L. The latter range can be at­ demineralized water and dilute to 1,000 mL. tained by interchanging the sample and diluent 5.2 Chloride working standards; Prepare a pump tubes. blank and 500 mL each of a series of chloride working standards by appropriate quantitative 2. Summary of method dilution of the chloride standard solution I, as This method is based on the displacement of follows: thiocyanate from mercuric thiocyanate by chloride and on the subsequent reaction of the Chloride standard solution Chloride concentration liberated thiocyanate ion with ferric ion to form (mL) (mg/L) the intensely colored ferric thiocyanate com­ 0.0 oo 5.0 5.0 plex. The absorbance of this complex is then 10.0 10.0 measured colorimetrically (O'Brien, 1962; Zall 20.0 20.0 and others, 1956). 30.0 30.0 50.0 50.0 60.0 60.0 Hg(SCN)2 + 2CH -> HgCl2 + 2SCN-1 80.0 80.0 100.0 100.0 SCN-1 + Fe+3 -> Fe(SCN)+2 5.3 Ferric nitrate stock solution, 121 g/L: 3. Interferences Dissolve 202 g Fe(NO3)3-9H2O in approx 500 Bromide, iodide, cyanide, thiosulfate, and mL demineralized water. Add 225 mL concen­ nitrite interfere. Color, depending upon its spec­ trated HN03 (sp gr 1.41) and dilute to 1 L, tral absorbance, may interfere with the photo­ Filter and store in an amber-colored container. metric measurement. 5.4 Mercuric thiocyanate stock solution, 4.17 g/L in methanol: Dissolve 4.17 g Hg(SCN)2 4. Apparatus in 500 mL methanol, dilute to 1 L with 4.1 Technicon AutoAnalyzer II, consisting methanol, and filter. of a sampler, proportioning pump, cartridge 5.5 Chloride color reagent: Add 150 mL fer­ manifold, colorimeter, voltage stabilizer, ric nitrate stock solution and 150 mL mercuric recorder, and printer. thiocyanate stock solution to demineralized 4.2 With this equipment the following water and dilute to 1 L. Add 1 mL/L of Brij-35 operating conditions have been found satisfac­ solution. Use amber bottle for storage. tory for the ranges from 10 to 100 mg/L and from 0.1 to 10.0 mg/L: 6. Procedure Absorption cell ——— 15 mm 6.1 Set up manifold (fig. 20). Wavelength ————— 480 nm 6.2 Allow colorimeter and recorder to warm Cam —————————— 60/h (6/1) for at least 30 min.

151 152 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

To sampler 4 Water wash -«- 0.073in receptacle 2.00 mL/min 0.040in Waste 0.60 mL/min 0.030in Air 0.32 mL/min O.OSOin Air 0.32 mL/min 14-turn coil 5-turn coil 0.025in Sample .23 mL/min

O.OSlin Diluent water 1.00 mL/min Sampler 4 Colorimeter 60/h 480 nm Color reagent 15-mm celL O.OSlin 6/lcam .00 mL/min

0.056 in Waste 1.20 mL/min Recorder Proportioning pump

Figure 20.—Chloride, ferric thiocyanate manifold

6.3 Adjust baseline to read zero scale divi­ 7. Calculations sions on the recorder with all reagents, but with 7.1 Prepare an analytical curve by plotting demineralized water in the sample line. the height of each standard peak versus its 6.4 Place a complete set of standards and a respective chloride concentration. blank in the first positions of the first sample 7.2 Compute the chloride-ion concentration tray, beginning with the most concentrated of each sample by comparing its peak height to standard. Place individual standards of differing the analytical curve Any baseline drift that may concentrations in approximately every eighth occur must be taken into account when com­ position of the remainder of this and subsequent puting the height of a sample or standard peak sample trays. Fill remainder of each tray with unknown samples. (NOTE 1). 8. Report NOTE 1. The sample cups should remain Report chloride, dissolved (00940), concentra­ sealed in their packages until just prior to use to tions as follows: less than 10 mg/L, one decimal; avoid contamination. Handle cups carefully to 10 mg/L and above, two significant figures. avoid contamination from perspiration on hands. 6.5 Begin analysis. When the peak from 9. Precision most concentrated working standard appears 9.1 Precision for 20 samples within the on the recorder, adjust the STD CAL control range of 0.3 to 246 mg/L may be expressed as until the flat portion of the peak reads full scale. follows: METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 153

Number of Mean Relative standard deviation ST=0.027X + 0.786 laboratories (mg/L) _____(percent)_____ 7 0.31 81 where 16 1.50 33 19 25.7 3 ST= overall precision, milligrams per liter, 9 58.8 3 6 122 6 and 12 246 3 X = concentration of chloride, milligrams per liter. References

O'Brien, J. E., 1962, Automatic analysis of chlorides in The correlation coefficient is 0.8935. sewage: Wastes Engineering, v. 33, p. 670-672. 9.2 Precision for six of the 20 samples ex­ Zall, D. M., Fisher, D., and Garner, M. Q., 1956, Photometric pressed in terms of the percent relative stand­ determination of chlorides in water: Analytical ard deviation is as follows: Chemistry, v. 28 p. 1665-1668.

Chloride, colorimetric, ferric thiocyanate, automated-discrete Parameter and Code: Chloride, dissolved, 1-2188-85 (mg/L as Cl): 00940

1. Application Wavelength ——— 480 nm This method may be used to determine con­ Absorption cell — 1 cm2, flow-through, centrations of chloride in surface, domestic, and temperature- industrial water in the ranges of 0.1 to 10.0 controlled mg/L and 10.0 to 500 mg/L. Samples contain­ Reaction temper­ ing greater concentrations need to be diluted. ature ————— 37 °C or ambient Sample volumes - 0.35 mL with 0.050 2. Summary of method mL of diluent for 2.1 This method is based on the displace­ 0.1 to 10.0 mg/L ment of thiocyanate from mercuric thiocyanate and 0.035 mL by chloride and on the subsequent reaction of with 0.065 mL of the liberated thiocyanate ion with ferric ion to diluent for 10.0 form the intensely colored ferric thiocyanate to 500 mg/L complex. The absorbance of this complex is then Reagent volumes 0.90 mL color measured colorimetrically (O'Brien, 1962; Zall reagent for 0.1 to and others, 1956). 10.0 mg/L and 1.4 mL color Hg(SCN)2 + 2C1-1 -* HgCl2 + 2SCN-1 reagent for 10.0 to 500 mg/L SCN'1 + Fe+3 -» Fe(SCN)+2 (NOTE 1)

NOTE 1. Sample-to-diluent ratio and reagent 2.2 For additional information see ASTM volumes must be optimized for each instrument Method D512-81, "Standard Methods of Test according to manufacturer's specifications. for Chloride Ion in Water" (American Society for Testing and Materials, 1984). 5. Reagents 5.1 Chloride standard solution I, 1.00 mL= 3. Interferences 10.00 mg Cl"1: Dissolve 16.485 g primary Bromide, iodide, cyanide, thiosulfate, and standard NaCl crystals, dried at 180 °C for nitrite interfere. Color, depending upon its spec­ 1 h, in demineralized water and dilute to tral absorbance, may interfere with the 1,000 mL. photometric measurement. 5.2 Chloride standard solution II, 1.00 mL= 0.10 mg Cl'1: Dilute 10.0 mL chloride standard 4. Apparatus solution I to 1,000 mL with demineralized 4.1 Discrete analyzer system, American water. Monitor IQAS or equivalent. 5.3 Chloride working standards, low range: 4.2 With this equipment the following Prepare a blank and 1,000 mL each of a series operating conditions have been found satisfac­ of chloride working standards by appropriate tory for the ranges from 0.1 to 10.0 mg/L and dilution of the chloride standard solution II as from 10,0 to 500 mg/L. follows: 155 156 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Chloride standard solution II Chloride concentration (ml) (mg/L) and for the high range use 10, 40, 80, 300, and 500 mg/L. Fill remainder of turntable with 00 000 1.00 .10 5.00 .50 6.3 Begin analysis. Printer will acknowledge 10.0 1.00 parameter and concentration range selected, 50.0 5.00 listing each sample-cup number and correspond­ 100.0 10.00 ing concentration. During each run the cathode- 5.4 Chloride working standards, high-range: ray tube (CRT) display will identify a plot of Prepare 1,000 mL each of a series of chloride standards and samples, and list blank and working standards by appropriate dilution of reagent optical densities with slope calculations. the chloride standard solution I, as follows: 7. Calculations Chloride standard solution II Chloride concentration Obtain the milligrams per liter of chloride in (mL) (mg/L) each sample from the printer. 4X) 40 8.0 80 30.0 300 8. Report 50.0 500 Report chloride, dissolved (00940), concentra­ tions as follows: less than 10 mg/L, one decimal; 5.5 Ferric nitrate stock solution, 121 g/L: 10 mg/L and above, two significant figures. Dissolve 202 g Fe(NO3)3-9H2O in approx 500 mL demineralized water. Add 225 mL concen­ 9. Precision trated HNO3 (sp gr 1.41) and dilute to 1 L. Precision expressed in terms of the standard Filter and store in an amber-colored container. deviation and percent relative standard devia­ 5.6 Mercuric thiocyanate stock solution, tion for replicate analysis by a single operator saturated: Add approx 5 g Hg(SCN)2 to 1 L is as follows: methanol. Mix thoroughly for 0.5 h and let stand. Remove excess Hg(SCN)2 by filtration. Mean Std. Deviation Relative standard deviation CAUTION—Poisonous. (mg/L) (mg/L) ____(percent)_____ 5.7 Chloride color reagent: Add 150 mL fer­ 0.38 0.06 16 ric nitrate stock solution and 150 mL mercuric 5.72 .07 1.2 thiocyanate stock solution to demineralized 15.0 .08 .5 21.4 1.0 4.7 water and dilute to 1 L. Store in amber bottle. 177 1.3 .7 Prepare fresh daily. References 6. Procedure 6.1 Set up analyzer and computer-card American Society for Testing and Materials, 1984, Annual assignments according to manufacturer's in­ book of ASTM Standards, section 11, water: Phila­ structions. delphia, v. 11.01, p. 392-400. 6.2 Place five standards and a blank, begin­ O'Brien, J. E., 1962, Automatic analysis of chlorides in sewage: Wastes Engineering, v. 33, p. 670-672. ning with the lowest concentration, in the first Zall, D. M., Fisher, D., and Garner, M. Q., 1956, Photometric positions on the sample turntable. For the low determination of chlorides in water: Analytical range use 0.10, 0.50,1.00, 5.00, and 10.0 mg/L, Chemistry, v. 28, p. 1665-1668. Chloride, titrimetric, mercurimetric

Parameter and Code: Chloride, dissolved, 1-1184-85 (mg/L as Cl): 00940

1. Application 3. Interferences This method may be used to determine chlor­ The method is not subject to interference from ide in water containing at least 0.1 mg/L of any of the anions and cations normally found chloride. Samples containing lower concen­ in natural waters; as much as 1,000 mg/L of trations need to be concentrated by nitrate, sulfate, phosphate, magnesium, and evaporation. calcium and 1X106 pg/L of aluminum do not in­ terfere. One thousand /*g/L of zinc, lead, nickel, 2. Summary of method ferrous, and chromous ions affect the colors of 2.1 Mercuric and chloride ions form a highly the solution, but not the accuracy of the titra­ stable, soluble complex. tion. Nickel ion at a concentration of 1X105 /xg/L is purple in neutral solution, green in acid Hg+2 + 2C1-1 ^ HgCl2 solution, but gray at the chloride end point. Cop­ per ion is tolerable up to 50,000 /xg/L. Chromate and ferric ions, if present at concentrations ex­ Thus, the chloride in a sample may be titrated ceeding 10,000 /*g/L, must be reduced to their with a standard solution of a soluble mercuric lower valence state prior to titration. The addi­ salt such as mercuric nitrate. The equivalence tion of dilute fresh hydroquinone solution point is detected by adding a small amount of insures reduction of these ions. Sulfite ion inter­ diphenylcarbazone to the sample. A slight ex­ feres at concentrations above 10 mg/L; the addi­ cess of mercuric ions, above that required to tion of a small amount of 30-percent hydrogen complex all of the chloride, reacts with this in­ peroxide eliminates sulfite interference. Bromide dicator to form a blue-violet complex (Dubsky and iodide are titrated with the chloride and Trtilek, 1933, 1934; Clarke, 1950). 2.2 The optimum pH range for the titration 4. Apparatus is between 3.0 and 3.6. If the titration is made 4.1 Buret, 5-, 10-, or 25-mL capacity. in a solution whose pH is less than 3.0, the 4.2 Fluorescent lamp, white. results will be high, and if in a solution of pH 4.3 Stirrer, magnetic. greater than 3.6, the results will be low (Clarke, 1950; Thomas, 1954). The proper pH for the 5. Reagents titration is easily obtained by adding bromo- 5.1 Chloride standard solution, 1.00 mL= phenol blue indicator and carefully adding dilute 1.00 mg Cl"1: Dissolve 1.648 g primary stand­ nitric acid or sodium hydroxide to adjust the ard NaCl crystals, dried at 180 °C for 1 h, in sample to the desired pH. demineralized water and dilute to 1,000 mL. 2.3 Two standard mercuric nitrate solutions 5.2 Hydrogen peroxide, 30-percent. are required. A dilute solution should be used 5.3 Hydroquinone solution, 1 g/100 mL: to titrate samples containing less than 200 Dissolve 1.0 g purified hydroquinone in demin­ mg/L chloride; a more concentrated mercuric eralized water and dilute to 100 mL. nitrate solution should be used to titrate sam­ 5.4 Mercuric nitrate standard solution I, ples containing more than 200 mg/L. 1.00 mL ol.OO mg Cl"1: Dissolve 4.832 g 157 158 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Hg(NO3)2-H2O in 25 mL demineralized water with attendant improvement in precision. Refer acidified with 0.25 mL concentrated HNO3 (sp to specific manufacturer's manual for detaila Re­ gr 1.41) and dilute to 1,000 mL. Filter, if neces­ agents are identical to those specified for the vis­ sary, and standardize by titrating 10.00 mL ual determination using the mercurimetric chloride standard solution diluted to 50 mL with method. demineralized water. 5.5 Mercuric nitrate standard solution II, 7. Calculations 1.00 mL 00.500 mg CH: Dissolve 2.416 g Hg(NO3)2'H2O in 25 mL demineralized water CH (mg/L) - acidified with 0.25 mL concentrated HNO3 (sp 1,000 X (mL titrant-mL blank) gr 1.41) and dilute to 1,000 mL. Filter, if neces­ mT, sample sary, and standardize by titrating 10.00 mL X (mg Cl per mL titrant) chloride standard solution diluted to 50 mL with demineralized water. 8. Report 5.6 Mixed indicator solution: Dissolve 0.5 g Report chloride, dissolved (00940), concentra­ crystalline diphenylcarbazone (Eastman Kodak tions as follows: less than 10 mg/L, one decimal; Na 4459) and 0.05 g bromophenol blue (Eastman 10 mg/L and above, two significant figures. Kodak No. 752) in 75 mL ethanol (methyl alcohol or specially denatured alcohol No. 3A are also 9. Precision suitable), and dilute to 100 mL with the alcohol 9.1 Precision for 36 samples within the range Store in a brown bottle; discard after 6 months. of 0.29 to 243 mg/L may be expressed as follows: 5.7 Nitric acid, 0.05M: Dilute 3.0 mL concen­ trated HNO3 (sp gr 1.41) to 1 L with demineral­ Sr = 0.045X4- 0.581 ized water. 5.8 Sodium hydroxide solution, 0.05M: where Dissolve 2.0 g NaOH in demineralized water and ST= overall precision, milligrams per liter, dilute to 1 L. and X= concentration of chloride, milligrams per 6. Procedure liter. 6.1 Pipet a volume of sample containing less than 20 mg CH (50.0 mL max) into a 125-mL The correlation coefficient is 0.8862. Erlenmeyer flask, and adjust the volume to ap- 9.2 Precision for seven of the 36 samples ex­ pressed in terms of the percent relative standard prox 50 mL. If the sample contains less than 0.1 deviation is as follows: mg/L of CH, evaporate an appropriate volume to 50 mL. Number of Mean Relative standard deviation 6.2 Place the flask on a magnetic stirrer and laboratories (mp/L) ____(percent)____ add 10 drops mixed indicator solution. 7 0.29 59 11 1.92 40 6.3 If a blue, blue-violet, or red color develops, 17 9.25 18 add 0.05M HNO3 by drops until the color 20 26.4 7 changes to yellow. Add 1.0 mL excess acid. If a 16 58.0 5 15 120 4 yellow or orange color forms when the mixed in­ 18 243 5 dicator is added, add 0.05M NaOH solution by drops until the color changes to blue violet; then References add 0.05M HNO3 by drops until the color Clarke, F. E., I960, Determination of chloride in water changes to yellow; then add 1 mL excess. Analytical Chemistry, v. 22, p. 553-5, 1458. 6.4 Titrate the solution with mercuric nitrate Dubsky, J. V.t and Tttilek, J., 1933, Microvolumetric analysis standard solution I or II until a blue-violet color using diphenylcarbazide and diphenylcarbazone as in­ persists throughout the solution. dicators (mercurimetry): Mikrochemie, v. 12, p, 315. 6.5 Determine a blank correction by similar­ ___1934, Mercurimetric determination of iodide using diphenylcarbazone as indicator Mikrochemie; v. 15, pi 95. ly titrating 50 mL demineralized water. Thomas, J. K, 1954, Mercurimetric determination of chlorides: 6.6 Alternatively, the end point of the titra- American Water Works Association Journal, v. 46, tion may be determined spectrophotometrically, PL 257-62. Chloride, titrimetric, Mohr

Parameter and Code: Chloride, dissolved, 1-1183-85 (mg/L as Cl): 00940

1. Application constant of chromic acid is small, and, therefore, 1.1 This procedure is recommended for water the chromate ion reacts with hydrogen ions. containing concentrations of chloride between 10 and 2000 mg/L, although it can be used CrO;2 + H+ 1 satisfactorily for measuring chloride concentra­ tions up to 5,000 mg/L. 1.2 Two titrant solutions of different concen­ The solution should not be too alkaline because trations are recommended. The more dilute of the limited solubility of silver hydroxide titrant is used when the chloride concentration (Collins, 1928). Calcium carbonate can be used is less than 200 mg/L. However, the end point to adjust the pH of acidic waters without is not as sharp as when a more concentrated danger of making the solution too alkaline. titrant is used, and the latter is recommended Detection of the end point is facilitated by il­ when the chloride concentration of the sample luminating the titration with yellow light or by exceeds 200 mg/L. In high-chloride waters, the viewing the titration through yellow goggles or voluminous precipitate tends to mask the end a filter. point, and the maximum amount of chloride 2.2 Additional information on the principle that can be titrated satisfactorily is about 50 of the determination is given by Kolthoff and mg. Excessive sample dilution decreases both others (1969). the precision and accuracy of the determination. Sample aliquots of less than 10 mL are not 3. Interferences recommended. Iodide and bromide titrate stoichiometrical- ly as chloride. Phosphate, sulfide, and cyanide 2. Summary of method interfere. Sulfide and cyanide can be removed 2.1 In the well-known Mohr method for by acidifying and boiling the sample, and then determination of chloride, the solution is satur­ adjusting the pH with calcium carbonate. ated with silver chloride at the equivalence Hydrogen sulfide can often be removed by pass­ point and contains equal concentrations of ing pure air through the sample. Sulfite in­ silver and chloride ions. When potassium chro- terferes but can be oxidized readily to sulf ate mate is used as an indicator, a slight excess of with hydrogen peroxide. silver precipitates as red-silver chromate. The following reactions occur: 4. Apparatus 4.1 Buret, 25-mL capacity. + Cl'1 ^ AgCl 4.2 Yellow light (or filter).

CrO;2 - Ag2Cr04 5. Reagents 5.1 Chloride standard solution, 1.00 mL= The pH for the titration should be between 7.0 1.00 mg CH: Dissolve 1.648 g primary stand­ and 10.5. In an acid medium, the sensitivity of ard NaCl crystals, dried at 180 °C for 1 h, in the method is decreased; the second ionization demineralized water and dilute to 1,000 mL. 159 160 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Potassium chromate indicator solution, 8. Report 5 g/100 mL: Dissolve 5 g K2CrO4 in 100 mL Report chloride, dissolved (00940), concentra­ demineralized water. Add silver standard solu­ tions as follows: less than 10 mg/L, one decimal; tion II until a small amount of red Ag2CrO4 10 mg/L and above, two significant figures. precipitates. Allow to stand overnight and filter to remove the Ag2CrO4. 9. Precision 5.3 Silver standard solution /, 1.00 mL o 9.1 Precision for 37 samples within the 5.00 mg CH. Pulverize approx 30 g AgNO3 range of 0.22 to 244 mg/L may be expressed as crystals in a clean mortar and dry at 105 to follows: 120°C. Discoloration of the crystals indicates decomposition caused by excessive drying tem­ perature or impurities. Dissolve 23.96 g dried = 0.036X + 0.532 AgNO3 in demineralized water and dilute to 950 mL. Standardize by titrating 25.00 mL chloride standard solution diluted to 50 mL. Store in a light-proof bottle where 5.4 Silver standard solution II, 1.00 mL o 0.50 mg Cl"1: Dilute 100 mL silver standard ST= overall precision, milligrams per liter, solution I with demineralized water to 1,000 mL. and Check the titer of the reagent by titrating 10.00 X = concentration of chloride, milligrams per mL chloride standard solution. Store in light- liter. proof bottle. The correlation coefficient is 0.8550. 9.2 Precision for seven of the 37 samples ex­ 6. Procedure pressed in terms of the percent relative stand­ 6.1 Pipet a volume of sample containing less ard deviation is as follows: than 50 mg CH (50.00 mL max) into a porce­ lain evaporating dish, and adjust the volume to approx 50 mL. Number of Mean Relative standard deviation laboratories (mg/L) _____(percent)_____ 6.2 Add 10 drops K2CrO4 indicator solution. 12 0.22 100 6.3 With constant stirring, titrate with silver 7 .29 72 standard solution I or II until the pink-red 10 8.59 13 Ag2CrO4 persists for 10 to 15 sec. 21 46.0 4 13 95.8 3 6.4 Determine a blank correction by similar­ 12 123 6 ly titrating 50 mL demineralized water. The nor­ 16 244 5 mal blank correction with silver standard solu­ tion II is 0.05 or 0.10 mL. No blank correction is required with the more concentrated titrant. References 7. Calculations Collins, W. D.. 1928, Notes on practical water analysis: U.S. Cl-1 (mg/L) = Geological Survey Water-Supply Paper 596-H, 1,000 X (mL titrant-mL blank) p. 235-266. mL sample Kolthoff, I. M., Sandell, E. B., Meehan, E. J., and Bruckens- tein, S., 1969, Quantitative chemical analysis [4th ed.]: X (mg CH per mL titrant) New York, MacMillan, 1199 p. Chloride, ion-exchange chromatographic, automated

Parameters and Codes: Chloride, dissolved, 1-2057-85 (mg/L as Cl): 00940 Chloride, dissolved, 1-2058-85 (mg/L as Cl): 00940

2. Summary of method in their acid form are measured using an elec­ Chloride is determined sequentially with six trical-conductivity cell. See method 1-2057, other anions by ion-exchange chromatography. anions, ion-exchange chromatographic, auto­ Ions are separated based on their affinity for the mated, and method 1-2058, anions, ion-exchange exchange sites of the resin. The separated anions chromatographic, precipitation, automated. 161

Chromium, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Chromium, dissolved, 1-1238-85 faglL as Cr): 01030 Chromium, total recoverable, I-3238-85 faQlL as Cr): 01034 Chromium, suspended recoverable, I -7238-85 (/*g/L as Cr): 01031

1. Application methyl isobutyl ketone (MIBK) is 3.1. At this 1.1 This method may be used to analyze water pH, however, manganese is also partially ex­ and water-suspended sediment containing from tracted. The manganese-APDC complex is 1 to 25 /ig/L of chromium. Samples containing unstable and decomposes to a fine suspension more than 25 /xg/L need either to be diluted prior of manganese oxides that clogs the atomizer- to chelation-extraction or to be analyzed by the burner. If the pH of the sample is adjusted to atomic absorption spectrometric direct method. 2.4 prior to chelation and extraction, less man­ 1.2 Suspended recoverable chromium is ganese is extracted, and there is only a slight calculated by subtracting dissolved chromium loss in extraction efficiency for chromium. If the from total recoverable chromium. extract is not clear after standing overnight, it 1.3 Total recoverable chromium in water- must be centrifuged. suspended sediment needs to undergo a prelim­ 3.2 Concentrations of iron greater than inary digestion-solubilization by method 1-3485 5,000 jug/L interfere by suppressing the before being determined. chromium absorption. 1.4 If the iron concentration of the sample exceeds 5,000 /tg/L, determine chromium by the 4. Apparatus atomic absorption spectrometric direct method. 4.1 Atomic absorption spectrometer equipped with electronic digital readout and 2. Summary of method automatic zero and concentration controls. 2.1 Chromium is determined by atomic ab­ 4.2 Refer to the manufacturer's manual to sorption spectrometry. Any trivalent chromium optimize instrument for the following: present is oxidized by potassium permanganate Grating ———————— Ultraviolet to the hexavalent state. The oxidized chromium, Wavelength ————— 357.9 nm together with hexavalent chromium originally Source (hollow-cathode present, is chelated with ammonium pyrrolidine lamp) ———————— Chromium dithiocarbamate (APDC) and extracted with Oxidant ———————— Air methyl isobutyl ketone (MIBK). The extract is Fuel —————————— Acetylene aspirated into the air-acetylene flame of the Type of flame ———— Reducing spectrometer (Midgett and Fishman, 1967). 4.3 Different burners may be used according 2.2 Excess permanganate is reduced with to manufacturers' instructions. sodium azide, which must not be present in ex­ cess because it interferes with subsequent pH 5. Reagents adjustment and chelation. 5.1 Ammonium pyrrolidine dithiocarbamate solution, 1.0 g/100 mL: Dissolve 1.0 g APDC in 3. Interferences demineralized water and dilute to 100 mL. 3,1 The optimum pH for the extraction of Prepare fresh daily. the hexavalent chromium-APDC complex by 5.2 Bromophenol blue indicator solution, 0.1 163 164 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS g/100 mL: Dissolve 0.1 g bromophenol blue in adjust the volume of each to approx 100 mL 100 mL 50-percent ethanol. with the acidified demineralized water. 5.3 Chromium standard solution I, 1.00 6.4 Add KMnO4 solution by drops to blank, mL=100 fig Cr+6: Dissolve 0.2829 g primary standards, and samples until a faint-pink color standard K2Cr2O7, dried for 1 h at 180 °C, in persists. demineralized water and dilute to 1,000 mL. 6.5 Heat on a steam bath for 20 min. If the 5.4 Chromium standard solution II, 1.00 color disappears, add KMnO4 solution by drops mL=2.00 jig Cr+3 Pipet 5.0 mL chromium to maintain a slight excess. standard solution I into an Erlenmeyer flask. 6.6 While blanks, samples, and standards Add approximately 15 mg Na2SO3 and 0.5 mL are still on the steam bath, add NaN3 solution concentrated HNO3 (sp gr 1.41). Gently by drops until KMnO4 color just disappears. evaporate just to dryness; strong heating re- Heat for about 2 min between each addition and oxidizes the Cr. Add 0.5 mL concentrated avoid adding any excess. Continue heating for HNO3 and again evaporate to dryness to 5 min after adding the last drop of sodium azide destroy any excess sulfite. Dissolve the residue solution. in 1 mL concentrated HNO3 with warming. 6.7 Transfer to a water bath and cool to Cool, transfer to a 250-mL volumetric flask, and room temperature. dilute to the mark with demineralized water. 6.8 Remove from the water bath and filter 5.5 Chromium standard solution III, 1.00 through Whatman No. 40 filter paper any sam­ mL=0.50 fig Cr+3: Dilute 25.0 mL chromium ple that has a brownish precipitate or coloration standard solution II to 100 mL with that may interfere with the pH adjustment. demineralized water. Prepare immediately 6.9 Add 2.0 mL IM NaOH and 2 drops before use. bromophenol blue indicator solution. Continue 5.6 Methyl isobutyl ketone (MIBK). the addition of IM NaOH by drops to all sam­ 5.7 Potassium permanganate solution, 0.32 ples and standards in which the indicator g/100 mL: Dissolve 0.32 g KMnO4 in demin­ change from yellow to blue has not occurred. eralized water and dilute to 100 mL. Allow to Add 0.12M H2SO4 by drops until the blue stand several days and decant if necessary. color just disappears; then add 2.0 mL in ex­ 5.8 Sodium azide solution, 0.10 g/100 mL: cess. The pH at this point should be 2.4 (NOTE Dissolve 0.10 g NaN3 in 100 mL demineralized 1). water. NOTE 1. The pH adjustment in paragraph 6.9 5.9 Sodium hydroxide solution, IM: Dis­ may be made with a pH meter instead of with solve 40 g NaOH in demineralized water and an indicator, in which case the filtration called dilute to 1 L. for in paragraph 6.8 will not be necessary. 5.10 Sulfuric acid, 0.12M: Cautiously, add 6.5 6.10 Add 5.0 mL APDC solution and shake mL concentrated H2SO4 (sp gr 1.84) to for 3 min. The pH at this point should be 2.8. demineralized water and dilute to 1 L. 6.11 Add 10.0 mL MIBK and shake vigorous­ ly for 3 min. 6. Procedure 6.12 Allow the layers to separate and then add 6.1 Clean all glassware used in this deter­ demineralized water until the ketone layer is mination with warm, dilute HNO3 (1 + 9) and completely in the neck of the flask. rinse with demineralized water immediately 6.13 Stopper and allow to stand overnight. before use. The Cr+6-APDC complex is stable for at least 6.2 Pipet a volume of sample solution con­ 36 h. taining less than 2.5 /xg Cr (100 mL max) into 6.14 Aspirate the ketone layer of the blank to a 200-mL volumetric flask, and adjust the set the automatic zero control. Use the auto­ volume to approx 100 mL. The pH must be 2.0 matic concentration control to set the concen­ or less. Add concentrated HNO3 if necessary. trations of standards. Use at least six 6.3 Acidify a liter of demineralized water standards. Calibrate the instrument each time with 1.5 mL concentrated HNO3 (sp gr 1.41). a set of samples is analyzed and check calibra­ Prepare a blank and at least six standards, and tion at reasonable intervals. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 165 7. Calculations val for the average standard deviation of 13.2 7.1 Determine the micrograms per liter of Mg/L ranged from 11.2 to 16.1 /*g/L. dissolved or total recoverable chromium in each 9.2 Precision for dissolved chromium for sample from the digital display or printer while seven of the 14 samples expressed in terms of aspirating each sample. Dilute those samples the percent relative standard deviation is as containing chromium concentrations that ex­ follows: ceed the working range of the method; repeat the chelation-extraction and multiply by the Number of Relative standard deviation proper dilution factors. laboratories (Mfl/L) _____(percent)____ 7.2 To determine the micrograms per liter of 4 5.75 66 suspended recoverable chromium, subtract dis- 3 9.67 6 solved-chromium concentration from total- 12 12.9 113 11 18.7 66 recoverable-chromium concentration. 3 20.0 39 3 44.3 9 8. Report 9 47.8 55 Report chromium, dissolved (01030), total- 9.3 It is estimated that the percent relative recoverable (01034), and suspended-recoverable (01031), concentrations as follows: less than 100 standard deviation for total recoverable and suspended recoverable chromium will be greater ptg/L, the nearest microgram per liter; 100 jig/L and above, two significant figures. than that reported for dissolved chromium.

9. Precision 9.1 The standard deviation for dissolved Reference chromium within the range of 5.8 to 47.8 /*g/L Midgett, M. R., and Fishman, M. J., 1967, Determination for 14 samples was found to be independent of of total chromium in fresh waters by atomic absorp­ concentration. The 95-percent confidence inter­ tion: Atomic Absorption Newsletter, v. 6, p. 128-131.

Chromium, atomic absorption spectrometric, direct

Parameters and Codes: Chromium, dissolved, 1-1236-85 faglL as Cr): 01030 Chromium, total recoverable, 1-3236-85 0*g/L as Cr): 01034 Chromium, suspended recoverable, t-7236-85 (/xg/L as Cr): 01031 Chromium, recoverable-from-bottom-material, 1-5236-85 0*g/g as Cr): 01029

1. Application absorption of the chromium. These in­ 1.1 This method may be used to analyze water terferences are eliminated in solutions contain­ and water-suspended sediment containing at ing about 18,000 mg/L of ammonium chloride least 10 Mg/L of chromium. Sample solutions (Barnes, 1966, and Giammarise, 1966). Samples containing more than 400 fig/L need to be adjusted to this concentration of ammonium diluted. Sample solutions containing less than chloride show no interferences from 7 X105 ngTL 10 /xg/L and brines need to be analyzed by the of iron and 10,000 /*g/L each of nickel and atomic absorption spectrometric chelation- cobalt, or from 1,000 mg/L of magnesium. extraction method, providing that the inter­ 3.2 Individual concentrations of sodium ference limits discussed in that method are not (8,000 mg/L), calcium (4,000 mg/L), nitrate (100 exceeded. mg/L), sulfate (8,000 mg/L), and chloride (10,000 1.2 Suspended recoverable chromium is mg/L) do not interfere. Greater concentrations calculated by subtracting dissolved chromium of each constituent were not investigated. from total recoverable chromium. 1.3 This method may be used to analyze bot­ 4. Apparatus tom material containing at least 1 jig/g of 4.1 Atomic absorption spectrometer chromium. Sample solutions containing more equipped with electronic digital readout and than 400 jig/L need to be diluted. automatic zero and concentration controls. 1.4 Total recoverable chromium in water- 4.2 Refer to the manufacturer's manual to suspended sediment needs to undergo prelim­ optimize instrument for the following: inary digestion-solubilization by method Grating ———————— Ultraviolet 1-3485, and recoverable chromium in bottom Wavelength ————— 357.9 nm. material needs to undergo preliminary Source (hollow-cathode digestion-solubilization by method 1-5485 lamp) ——————— Chromium before being determined. Oxidant ———————— Air Fuel —————————— Acetylene 2. Summary of method Type of flame ———— Reducing Chromium is determined by atomic absorp­ 4.3 The 102-xnm, flathead, single-slot burner tion spectrometry by direct aspiration of the allows a working range of 10 to 400 jtg/L. Dif­ sample solution into an air-acetylene flame. Am­ ferent burners may be used according to monium chloride is added to the sample to mask manufacturers1 instructions. certain interferences. 3. Interferences 5. Reagents 3.1 Iron, nickel, and cobalt at 100 jxg/L and 5.1 Ammonium chloride solution, 200 g/L: magnesium at 30 mg/L, in the prepared sam­ Dissolve 200 g NH4C1 in demineralized water ple solution, interfere by suppressing the and dilute to 1 L. 167 168 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Chromium standard solution /, 1.00 mL— (01031), concentrations as follows: less than 100 /ig Cr: Dissolve 0.2829 g primary standard 1,000 Mg/L. nearest 10 /ig/L: 1,000 pgFL and K2Cr2O7> dried for 1 h at 180 °C, in demineral­ above, two significant figures. ized water and dilute to 1,000 mL. 8.2 Report chromium, recoverable-from- 5.3 Chromium standard solution II, 1.00 mL= bottom-material (01029), concentrations as 1.00 fig Cr: Dilute 10.0 mL chromium standard follows: less than 10 pg/g, nearest microgram solution I to 1,000 mL with demineralized water. per gram; 10 to 100 j*g/g, nearest 10 Mg/g; 100 5.4 Chromium standard working solutions: and above, two significant figures. Prepare a series of at least six standard working solutions containing from 10 to 400 /xg/L of 9. Precision chromium by diluting chromium standard solu­ 9.1 The standard deviation for dissolved tion II. Tb each standard working solution, add chromium within the range of 6.7 to 55 /ig/L for 1.0 mL of NH4C1 solution for each 10 mL of 23 samples was found to be independent of con­ standard. Similarly, prepare a demineralized centration. The 95-percent confidence interval water blank. for the average standard deviation of 7.2 /*g/L 6. Procedure ranged from 6.7 to 7.9 /ig/L. 6.1 Add 1.0 mL NH4C1 solution to 10.0 mL 9.2 Precision for dissolved chromium for five sample solution and mix thoroughly. of the 23 samples expressed in terms of the per­ 6.2 Aspirate the blank to set the automatic cent relative standard deviation is as follows: zero control Use the automatic concentration control to set the concentrations of standards. Number of Relative standard deviation Use at least six standards. Calibrate the instru­ laboratories WM _____(percent)_____ ment each time a set of samples is analyzed and 6 6.7 77 23 10.9 54 check calibration at reasonable intervals. 23 18.7 46 13 30.2 19 7. Calculations 6 55.0 19 7.1 Determine the rnicrograms per liter of dis­ solved or total recoverable chromium in each 9.3 It is estimated that the percent relative sample from the digital display or printer while standard deviation for total recoverable and aspirating each sample Dilute those samples suspended recoverable chromium and for containing chromium concentrations that exceed recoverable chromium from bottom material the working range of the method and multiply will be greater than that reported for dissolved by the proper dilution factors. chromium. 7.2 Tb determine the micrograms per liter of 9.4 Precision for total recoverable chromium suspended recoverable chromium, subtract dis- expressed in terms of percent relative standard solved-chromium concentration from total- deviation for two water-suspended sediment recoverable-chromium concentration. mixtures is as follows: 7.3 Tb determine micrograms per gram of chromium in bottom-material samples first deter­ Number of Mean Relative standard deviation mine the micrograms per liter of chromium in laboratories fcg/L) _____(percent)_____ each sample as in paragraph 7.1; then 8 31.6 22 11 27.3 38 mL of original digest CrX Cr (Mg/g) = 1.000_____ References wt of sample (g) Barnes, L., Jr., 1966, Determination of chromium in low alloy steels by atomic absorption spectrometry: Analytical 8. Report Chemistry, v. 38, p. 1083-1085. Giammarise, A., 1966, The use of ammonium chloride in 8.1 Report chromium, dissolved (01030), total- analyses of chromium samples containing iron: Atomic recoverable (01034), and suspended-recoverable Absorption Newsletter, v. 5, p. 113-115. Chromium, atomic absorption spectrometric, graphite furnace

Parameter and Code: Chromium, dissolved, 1-1235-85 (/*g/L as Or): 01030

1. Application Calcium (25 mg/L), magnesium (8 mg/L), sodium 1.1 This method may be used to determine (20 mg/L), sulfate (34 mg/L), and chloride (25 chromium in low ionic-strength water and pre­ mg/L) do not interfere. Greater concentrations cipitation. With deuterium background cor­ of these constituents were not investigated. rection and a 20-piL sample, the method is 3.2 Precipitation samples usually contain applicable in the range from 0.2 to 20 /ig/L. With very low concentrations of chromium. Special Zeeman background correction and a 20-/xL precautionary measures must be employed dur­ sample, the method is applicable in the range ing both sample collection and laboratory deter- from 0.5 to 25 /*g/L. Sample solutions that con­ mination to prevent contribution from tain chromium concentrations exceeding the contamination. upper limits must be diluted or preferably be analyzed by the atomic absorption spectro­ 4. Apparatus metric direct or chelation-extraction method. 4.1 Atomic absorption spectrometer, for use 1.2 The analytical range and detection limits at 357.9 nm and equipped with background cor­ can be increased or possibly decreased by vary­ rection, digital integrator to quantitate peak ing the volume of sample injected or the in­ areas, graphite furnace with temperature pro­ strumental settings. Purification of reagents grammer, and automatic sample injector. The and use of ASTM Type 1 water {Method programmer must have high-temperature ramp­ D-1193, American Society for Testing and ing and stopped-flow capabilities. Materials, 1984) may result in lower detection 4.1.1 Refer to the manufacturer's manual to limits. optimize instrumental performance. The ana­ lytical ranges reported in paragraph 1.1 are for 2. Summary of method a 20-jtL sample with 5 /*L of matrix modifier Chromium is determined by atomic absorp­ (NOTE 1). tion spectrometry in conjunction with a graph­ NOTE 1. A 20-jtL sample generally requires ite furnace containing a graphite platform 30 s to dry. Samples that have a complex matrix (Hinderberger and others, 1981). A sample is may require a longer drying and charring time. placed on the graphite platform and a matrix 4.1.2 Graphite furnace, capable of reaching modifier is added. The sample is then evapo­ temperatures sufficient to atomize the element rated to dryness, charred, and atomized using of interest. Warning: dial settings frequently high-temperature ramping. The absorption sig­ are inaccurate and newly conditioned furnaces nal generated during atomization is recorded require temperature calibration. and compared with standards. 4.1.3 Graphite tubes and platforms. Pyrolytically coated graphite tubes and solid 3. Interferences pyrolytic graphite platforms are recommended. 3.1 Interferences in low ionic-strength sam­ 4.2 Lab ware. Many trace metals at very low ples, such as precipitation, normally are quite concentrations have been found to sorb very low. In addition, the use of the graphite plat­ rapidly to glassware. To preclude this, fluori- form reduces the effects of many interferences. nated ethylene propylene (FEP) or Teflon 169 170 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS labware may be used. Alternately, glassware, (sp gr 1.41): J. T. Baker "Ultrex" brand HNO3 particularly flasks and pipets, may be treated has been found to be adequately pure; however, with silicone anti-wetting agent such as Surfacil each lot must be checked for contamination. (Pierce Chemical Co., Rockford, IL, 61105) ac­ Analyze acidified Type 1 water for chromium. cording to the manufacturer's instructions. Add an additional 1.5 mL of concentrated Autosampler cups must be checked for con­ HNO3/liter of water, and repeat analysis. In­ tamination. Lancer (1831 Olive St., St. Louis, tegrated signal should not increase by more MO, 63103) polystyrene disposable cups have than 0.001 absorbance-seconds. been found to be satisfactory after acid rinsing. 5.7 Water, acidified, Type 1: Add 1.5 mL Alternately, reuseable Teflon or FEP cups may high-purity concentrated HNO3 (sp gr 1.41) to be used. each liter of water. 4.3 Argon, standard, welder's grade, com­ 5.8 Water, Type 1 mercially available. Nitrogen may also be used if recommended by the instrument manu­ 6. Procedure facturer 6.1 Systematically clean and rinse work areas with deionized water on a regular sched­ 5. Reagents ule. Use a laminar flow hood or a "clean room" 5.1 Chromium standard solution I, 1.00 environment during sample transfers. Ideally, mL=1,000 pg Cr: Dissolve 2.8290 g primary the autosampler and the graphite furnace standard K2Cr2O7, dried for 1 h at 180 °C, in should be in a clean environment. Type 1 water. Add 10 mL high-purity, concen­ 6.2 Soak autosampler cups at least over­ trated HNO3 (sp gr 1.41), Ultrex or equivalent, night in a 1 + 1 solution of Type 1 water and and dilute to 1,000 mL with Type 1 water. high-purity nitric acid. 5.2 Chromium standard solution II, 1.00 6.3 Rinse the sample cups twice with sam­ mL=10.0 fig Cr: Dilute 10.0 mL chromium ple before filling. Place cups in sample tray and standard solution I to 1,000 mL (NOTE 2). cover. Adjust sampler so that only the injection NOTE 2. Use acidified Type 1 water (para­ tip contacts the sample. graph 5.7) to make dilutions. All standards 6.4 In sequence, inject 20-/*L aliquots of must be stored in sealed Teflon or FEP con­ blank and working standards plus 5 /iL of tainers. Each container must be rinsed twice modifier each and analyze. Analyze the blank with a small volume of standard before being and working standards twice. Construct the filled. Standards stored for 6 months in FEP analytical curve from the integrated peak areas containers yielded values equal to those of (absorbance-seconds). Generally, the curve freshly prepared standards. should be linear to a peak-absorbance (peak* 5.3 Chromium standard solution III, 1.00 height) value of 0.40 absorbance units. mL=1.00 jig Cr: Dilute 100.0 mL chromium 6.5 Similarly, inject and analyze the samples standard solution II to 1,000 mL. This stand­ twice. Every tenth sample cup should contain ard is used to prepare working standards serial­ either a standard or a reference material. ly at time of analysis. 6.6 Restandardize as required. Minor 5.4 Chromium standard solution IV, 1.00 changes of values for known samples usually in­ mL=0.01 fig Cr: Dilute 10.0 mL chromium dicate deterioration of the furnace tube, contact standard solution III to 1,000 mL. This stand­ rings, and/or platform. A major variation usual­ ard also is used to prepare working standards ly indicates either autosampler malfunction or serially at time of analysis. residue buildup from a complex matrix in a 5.5 Matrix modifier solution, 4.0 g previous sample. Mg(NO3)2/L, Suprapur MCB reagent or equivalent: Add 6.9 g Mg(NO3)2-6H2O to 950 7. Calculations mL Type 1 water, mix, and dilute to 1,000 mL. Determine the micrograms per liter of chrom­ DO NOT ADD ACID TO THE PURIFIED ium in each sample from the digital display or MATRIX MODIFIER SOLUTION. printer output. Dilute those samples containing 5.6 Nitric acid, concentrated, high-purity, concentrations of chromium that exceed the METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 171 working range of the method; repeat the anal­ 9.4 The precision and bias for the deuterium ysis, and multiply by the proper dilution factors. background method were tested on deionized water and tap water (specific conductance 280 8. Report /iS/cm). A known amount of chromium was Report chromium, dissolved (01030), concen­ added to each sample, and single-operator preci­ trations as follows: less than 10.0 fig/L, nearest sion and bias for six replicates are as follows: 0.1 /tg/L; 10 pg/L and above, two significant figures for both deuterium background correc­ Relative Amount Amount Standard standard tion and Zeeman background correction. added found deviation deviation Recovery (pg/L) (/*g/L) 0*g/L) (percent) (percent) 9. Precision Deionized water 9.1 Analysis of one sample 15 times by a 2.2 2.22 0.41 18.5 101 single operator using deuterium background 4.4 4.79 .28 5.8 109 correction is as follows: 8.0 8.09 .46 5.7 101 8.5 7.92 .56 7.1 93 16 15.45 .91 5.9 97 Mean Standard deviation Relative standard deviation fog/L)

Mean Standard deviation Relative standard deviation 9.5 The standard deviation from interlabor- WL) (MQ/L) (percent) atory data, without regard to type of back­ 7.30 0.17 2.3 ground correction and use of matrix modifiers, 11.63 .18 1.5 17.53 .16 .9 if any, for dissolved chromium within the range 23.63 .20 .8 of 4.6 to 30.8 jtg/L for 16 samples, was found to be independent of concentration. The 9.3 The precision and bias for the Zeeman 95-percent confidence interval for the average background correction were tested on deionized standard deviation of 5.0 jig/L ranged from 4.5 water and tap water (specific conductance 280 to 5.6 /xg/L. fjtSlcm). A known amount of chromium was add­ ed to each sample, and single-operator precision and bias for six replicates are as follows: References American Society for Testing and Materials, 1984, Annual Relative book of ASTM standards, section 11, water: Philadel­ Amount Amount Standard standard added found deviation deviation Recovery phia, v. 11.01, p. 39-41. (pg/L) (MQ/U (MO/U) (percent) (percent) Cooksey, M., and Barnett, W. B., 1979, Matrix modifica­ tion and the method of additions in flameless atomic Deionized water absorption: Atomic Absorption Newsletter, v. 18, 2.2 2.43 0.29 11.9 110 p. 101-5. 4.4 5.08 .37 7.3 115 Fernandez, F. J., Beatty, M. M., and Barnett, W. B., 1981, 8.0 7.6 .42 5.5 95 Use of the L'vov platform for furnace atomic absorp­ 8.5 7.93 .64 8.1 93 tion applications: Atomic Spectroscopy, v. 2, p. 16-21. 16 15.38 .34 2.2 96 Hinderberger, E. J., Kaiser, M. L., and Koirtyohann, S. R., Tap water 1981, Furnace atomic absorption analysis of biological samples using the L'vov platform and matrix modifica­ 2.2 2.37 .51 21.5 108 tion: Atomic Spectroscopy, v. 2, p. 1-11. 4.4 4.53 .96 21.2 103 Manning, D. C., and Slavin, W., 1983, The determination 8.0 7.17 1.43 19.9 90 of trace elements in natural waters using the stabilized 8.5 7.53 1.17 7.0 89 temperature platform furnace: Applied Spectroscopy, 16 13.90 2.13 15.3 87 v. 37, p. 1-11. 172 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Ottaway, J. M., 1982, A revolutionary development in Slavin, WM Carnrick, G. It, and Manning, D. C, 1982, Magnesi­ graphite furnace atomic absorption: Atomic Spec- um nitrate as a matrix modifier in the stabilized tempera­ troscopy, v. 3, p. 89-92. ture platform furnace: Analytical Chemistry, v. 54, p 621-4. Chromium, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Chromium, total 1-5474-85 (mg/kg as Cr): none assigned

2. Summary of method hotplate at 200 °C. Chromium is determined on A sediment sample is dried, ground, and ho­ the resulting solution by atomic absorption mogenized. The sample is digested with a spectrometry. See method 1-5474, metals, ma­ combination of nitric, hydrofluoric, and per­ jor and minor, total-in-sediment, atomic absorp­ chloric acids in a Teflon beaker heated on a tion spectrometric, direct. 173

Chromium, hexavalent, atomic absorption spectrometric, chelatiorv extraction

Parameter and Code: Chromium, hexavalent, dissolved, 1-1232-85 (pg/L as Cr): 01032

1. Application 4.3 Different burners may be used according 1.1 This method may be used to analyze water to manufacturers' instructions. and brines containing from 1 to 25 jig/L of chromium. Samples containing more than 25 5. Reagents figfL need to be diluted prior to chelation- 5.1 Ammonium pyrrolidine dithiocarbamate extr action. (APDC) solution, 1.0 g/100 mL: Dissolve 1.0 g 1.2 If the iron concentration of the sample APDC in demineralized water and dilute to 100 exceeds 5,000 Mg/L, determine hexavalent mL. Prepare fresh daily. chromium by the colorimetric diphenylcar- 5.2 Chromium standard solution /, 1.00 bazide method (1-1230). mL=100 jig Cr+6: Dissolve 0.2829 g primary standard K2Cr2O7, dried for 1 h at 180°C, in 2. Summary of method demineralized water and dilute to 1,000 mL. Hexavalent chromium is determined by 5.3 Chromium standard solution //, 1.00 atomic absorption spectrometry. The element mL=10.0 /*g Cr+6: Dilute 100 mL chromium is chelated with ammonium pyrrolidine dithio- standard solution I to 1,000 mL with demin­ carbamate (APDC) and extracted with methyl eralized water. isobutyl ketone (MIBK). The extract is aspi­ 5.4 Chromium standard solution ///, 1.00 rated into the air-acetylene flame of the spec­ mL=0.10 /ig Cr+6: Dilute 10.0 mL chromium trometer (Midgett and Fishman, 1967). standard solution II to 1,000 mL with demin­ eralized water. 3. Interferences 5.5 Methyl isobutyl ketone (MIBK). Concentrations of iron greater than 5,000 5.6 Sodium hydroxide solution, 2.5M: /ig/L interfere by suppressing the chromium ab­ Dissolve 100 g NaOH in demineralized water sorption. and dilute to 1 L. Alternately a 2.5M NH4OH solution may be used. Add 167 mL concentrated 4. Apparatus NH4OH (sp gr 0.90) to 600 mL demineralized 4.1 Atomic absorption spectrometer water. Mix, cool.and dilute to 1L with demin­ equipped with electronic digital readout and eralized water. automatic zero and concentration controls. 4.2 Refer to the manufacturer's manual to 6. Procedure optimize instrument for the following: 6.1 Clean all glassware used in this deter­ Grating ——————— Ultraviolet mination with warm, dilute HNO3 (1+9) and Wavelength ————— 357.9 nm rinse with demineralized water immediatley Source (hollow-cathode before use. lamp) ———————— Chromium 6.2 Pipet a volume of sample containing less Oxidant ———————— Air than 2.5 jig Cr+6 (100 mL max) into a 200-mL Fuel —————————— Acetylene volumetric flask, and adjust the volume to ap- Type of flame ———— Reducing prox 100 mL. 175 176 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6.3 Acidify a liter of demineralized water digital display or printer while aspirating each with 1.5 mL concentrated HNO3 (sp gr 1.41). sample. Dilute those samples containing Prepare a blank and at least six standards con­ chromium concentrations that exceed the work­ taining from 1 to 25 /xg/L of Cr+6, and adjust ing range of the method; repeat the chelation- the volume of each to approx 100 mL with the extraction and multiply by the proper dilution acidified demineralized water. factor. 6.4 With a pH meter, adjust the pH of each solution to 2.4 by dropwise addition of 2.5Af 8. Report NaOH or NH4OH. Report chromium, dissolved, hexavalent 6.5 Add 5.0 mL APDC solution and mix. (01032), concentrations as follows: less than 10 6.6 Add 10.0 mL MIBK and shake vigorous­ /xg/L, nearest microgram per liter; 10 #ig/L and ly for 3 min. above, two significant figures. 6.7 Allow the layers to separate and add demineralized water until the ketone layer is completely in the neck of the flask. The Cr+6 9. Precision -APDC complex is stable for at least 36 h. It is estimated that the precision of this 6.8 Aspirate the ketone layer of the blank to method for Cr+6 is equal to total chromium by set the automatic zero control. Use the auto­ the atomic absorption spectrometric chelation- matic concentration control to set the concen­ extraction method. trations of of standards. Use at least six standards. Calibrate the instrument each time a set of samples is analyzed and check calibra­ Reference tion at reasonable intervals. Midgett, M. R., and Fishman, M. J.f 1967, Determin­ 7. Calculations ation of total chromium in fresh waters by atomic ab­ Determine the micrograms per liter of hex- sorption: Atomic Absorption Newsletter, v. 6, p. avalent chromium in each sample from the 128-131. Chromium, hexavalent, colorimetric, diphenylcarbazide

Parameter and Code: Chromium, hexavalent, dissolved, 1-1230-85 (jig/L as Cr + 6): 01032

1. Application 5. Reagents This method may be used to analyze most 5.1 Chromium standard solution, 1.00 mL= natural water containing from 50 to 4,000 /*g/L 100 /*g Cr+6: Dissolve 0.2829 g primary stand­ hexavalent chromium. Samples containing ard K2Cr2O7, dried for 1 h at 180 °C, in higher concentrations must first be diluted. demineralized water and dilute to 1,000 mL. 5.2 Diphenylcarbazide reagent: Dissolve 0.2 2. Summary of method g diphenylcarbazide and 1.0 g phthalic 2.1 This method determines only hexavalent anhydride in 200 mL ethanol. This reagent is chromium in solution. stable for several weeks; a slight discoloration 2.2 In acid solution, diphenylcarbazide and will not impair the usefulness of the reagent. hexavalent chromium form a soluble red- violet 5.3 Sulfuric acid, 1.2M: CAUTIOUSLY, add product that absorbs light at 540 nm. The pH 6.5 mL concentrated H2SO4 (sp gr 1.84) to of the reaction is not particularly critical; solu­ demineralized water and dilute to 100 mL. tions differing in pH from 0.7 to 1.3 give identi­ cal colors. The color of the chromium-diphenyl- 6. Procedure carbazide product changes slightly with time, 6.1 Pipet a volume of sample containing less but for practical purposes it can be considered than 40 jig Cr+6 (10.0 mL max) into a 50-mL stable. beaker, and adjust the volume to 10.0 mL with 2.3 Additional information on the principle demineralized water. of the determination is given by Sandell (1950). 6.2 Prepare a blank of demineralized water and sufficient standards, and adjust the volume 3. Interferences of each to 10.0 mL with demineralized water. For all practical purposes the reaction is spe­ 6.3 Add 1.0 mL 1.2M H2SO4 and mix. cific for chromium; metallic interference almost 6.4 Add 0.5 mL diphenylcarbazide reagent never occurs. Iron, mercury, and molybdenum and mix. in concentrations as high as 100,000 /*g/L show 6.5 Allow to stand 10 min. only a small effect. Vanadium should not be 6.6 Determine the absorbance of the sample present in concentrations exceeding 4,000 pglL. and standards against the blank, and when nec­ The effect of water color is small, and color as essary make a correction for water color. much as 50 color units (Hazen scale) is tolerable The chromium color develops almost instantly 7. Calculations and is stable; whereas, vanadium color develops 7.1 Determine micrograms hexavalent instantly and then fades rapidly. If the original chromium in the sample from a plot of absorb- vanadium concentration is less than 4,000 jig/L, ances of standards. no vanadium color persists after 10 min. 7.2 Determine the hexavalent chromium con­ centration in micrograms per liter as follows: 4. Apparatus 4.1 Spectrometer for use at 540 nm. 4.2 Refer to the manufacturer's manual for x **g-———— Cr+6 i*- ————— sample optimizing instrument. mL sample 177 178 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Number of Relative standard deviation 8. Report laboratories _____(percent)______Report chromium, dissolved hexavalent 810 (01032), concentrations as follows: 50 to 100 /ig/L, nearest 10 jig/L; 100 ^g/L and above, two significant figures. Reference

9. Precision Sandell, E. B., I960, Colorimetric determination of traces Precision expressed in terms of the percent of metals <2d ed.): New York, Interscience Publishers, relative standard deviation is as follows: p. 260. Cobalt, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Cobalt, dissolved, 1-1240-85 (/*g/L as Co): 01035 Cobalt, total recoverable, I-3240-85 (^g/L as Co): 01037 Cobalt, suspended recoverable, (-7240-85 (jig/L as Co): 01036

1. Application 4.2 Refer to the manufacturer's manual to 1.1 This method may be used to analyze optimize instrument for the following: water, brines, and water-suspended sediment Grating ——————— Ultraviolet containing from 1 to 50 /tg/L of cobalt. Sample Wavelength ————— 240.7 nm solutions containing more than 50 j*g/L need Source (hollow-cathode either to be diluted prior to chelation-extraction lamp) ———————— Cobalt or to be analyzed by the atomic absorption spec­ Oxidant ———————— Air trometric direct method. Fuel ————————— Acetylene 1.2 Suspended recoverable cobalt is Type of flame ———— Oxidizing calculated by subtracting dissolved cobalt from 4.3 Different burners may be used according total recoverable cobalt. to manufacturers' instructions. 1.3 Total recoverable cobalt in water- suspended sediment needs to undergo a pre­ 5. Reagents liminary digestion-solubilization by method 5.1 Ammonium pyrrolidine dithiocarba­ 1-3485 before being determined. mate solution, 1 g/100 mL: Dissolve 1 g APDC 1.4 If the iron concentration of the sample so­ in 100 mL demineralized water. Prepare fresh lution exceeds 25,000 /xg/L, determine cobalt by daily. atomic absorption spectrometric direct method. 5.2 Citric acid-sodium citrate buffer solution: Dissolve 126 g citric acid monohydrate and 44 2. Summary of method g sodium citrate dihydrate in demineralized Cobalt is determined by atomic absorption water and dilute to 1 L with demineralized spectrometry following chelation with am­ water. See NOTE 3 before preparation. monium pyrrolidine dithiocarbamate (APDC) 5.3 Cobalt standard solution /, 1.00 mL= and extraction with methyl isobutyl ketone 100 /ig Co: Dissolve 0.1407 g Co2O3 in a mini­ (MIBK). The extract is aspirated into an air- mum amount of dilute HNO3. Add 10 mL acetylene flame of the spectrometer (Fishman concentrated HNO3 (sp gr 1.41) and dilute to and Midgett, 1968). 1000 mL with demineralized water. 5.4 Cobalt standard solution II, 1.00 mL= 3. Interferences 2.0 /Ag Co: Dilute 20.0 mL cobalt standard solu­ Concentrations of iron greater than 25,000 tion I and 1 mL concentrated HNO3 (sp gr 1.41) figlL interfere by suppressing the cobalt ab­ to 1,000 mL with demineralized water. sorption. 5.5 Cobalt standard solution III, 1.00 mL= 0.2 fjLg Co: Immediately before use, dilute 10.0 4. Apparatus mL cobalt standard solution II to 100.0 mL 4.1 Atomic absorption spectrometer with acidified water. This standard is used to equipped with electronic digital readout and prepare working standards at the time of automatic zero and concentration controls. analysis. 179 180 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.6 Methyl isobutyl ketone (MIBK). analyzed and check calibration at reasonable 5.7 Potassium hydroxide solution, 10M: intervals. Dissolve 56 g KOH in demineralized water, cool, and dilute to 100 mL. 7. Calculations 5.8 Potassium hydroxide solution, 2.5M: 7.1 Determine the micrograms per liter of Dissolve 14 g KOH in demineralized water and dissolved or total recoverable cobalt in each dilute to 100 mL (NOTE 1). sample from the digital display or printer. NOTE 1. Alternatively, a 2.5M NH4OH solu­ Dilute those samples containing cobalt concen­ tion may be used. Add 167 mL concentrated trations that exceed the working range of the NH4OH (sp gr 0.90) to 600 mL demineralized method; repeat the chelation-extraction, and water. Cool, and dilute to 1 L. multiply by the proper dilution factors. 5.9 Water, acidified: Add 1.5 nnL concen­ 7.2 To determine the micrograms per liter of trated HNO3 (sp gr 1.41) to 1L of demineralized suspended recoverable cobalt, subtract dis- water. solved-cobalt concentration from total-recover­ able-cobalt concentration. 6. Procedure 6.1 Clean all glassware used in this deter* 8. Report initiation with warm, dilute HNO3 (1 + 9) and Report cobalt, dissolved (01035), total- rinse with demineralized water immediately recoverable (01037), and suspended-recoverable before use. (01036), concentrations as follows: less than 100 6.2 Pipet a volume of sample solution con­ jxg/L, nearest microgram per liter; 100 jtg/L and taining less than 5.0 /*g Co (100 mL max) into above, two significant figures. a 200-mL volumetric flask, and adjust the volume to approx 100 mL. 9. Precision 6.3 Prepare a blank of acidified water and 9.1 The standard deviation for dissolved sufficient standards, and adjust the volume of cobalt within the range of 2.0 to 14.0 /*g/L for each to approx 100 mL with acidified water. 17 samples was found to be independent of con­ 6.4 With a pH meter, adjust the pH of each centration. The 95-percent confidence interval solution to 2.7 with 2.5M KOH (NOTES 2 and for the average standard deviation of 1.6 /*g/L 3). Shake for 3 znin. ranged from 1.4 to 1.9 j*g/L. NOTE 2. For water-suspended sediment sam­ 9.2 Precision for dissolved cobalt for five of ples that have been digested, add 1 to 2 mL 10M the 17 samples expressed in terms of the per­ KOH or concentrated NH4OH (sp gr 0.90) cent relative standard deviation is as follows: before pH adjustment. Number of Mean Relative standard deviation NOTE 3. If an automated titration system is laboratories _____(percent) _____ used to adjust the pH, add 2.5 mL citric acid- 3 2.0 0 sodium citrate buffer solution prior to pH ad­ 6 2.2 79 justment. This will prevent over-shooting the 9 5.3 23 end point in poorly buffered samples. 5 11.4 13 8 14.0 14 6.5 Add 2.5 mL APDC solution and mix. 6.6 Add 10.0 mL MIBK and shake vigorous­ 9.3 It is estimated that the percent relative ly for 3 min. standard deviation for total recoverable and 6.7 Allow the layers to separate and add suspended recoverable cobalt will be greater demineralized water until the ketone layer is than that reported for dissolved cobalt. completely in the neck of the flask. 6.8 Aspirate the ketone layer within 1 h. Reference Aspirate the ketone layer of the blank to set the automatic zero control. Use the automatic con­ Fishman, M. J.t and Midgett, M. R., 1968, Extraction tech­ niques for the determination of cobalt, nickel, and lead centration control to set the concentrations of in fresh water by atomic absorption, in Trace inorganics standards. Use at least six standards. Calibrate in water: American Chemical Society, Advances in the instrument each time a set of samples is Chemistry Series, no. 73, p. 230-5. Cobalt, atomic absorption spectrometric, direct

Parameters and Codes: Cobalt, dissolved, 1-1239-85 fcg/L as Co): 01035 Cobalt, total recoverable, 1-3239-85 (jig/U as Co): 01037 Cobalt, suspended recoverable, I-7239-85 (uglL as Co): 01036 Cobalt, recoverable-from-bottom-material, dry wt, I -5239-85, (pg/g as Co): 01038

1. Application is eliminated in solutions containing about 1.1 This method may be used to analyze water 18,000 mg/L of ammonium chloride. Samples and water-suspended sediment containing at adjusted to this concentration of ammonium least 50 /ig/L of cobalt. Samples solutions con­ chloride show no interference from 800 mg/L of taining more than 1,000 /ig/L need either to be nitrate. diluted or to be read on a less expanded scale. 3.2 Individual concentrations of sodium Sample solutions containing less than 50 /ig/L (9,000 mg/L), potassium (9,000 mg/L), calcium need to be analyzed by the atomic absorption (4,500 mg/L), magnesium (4,500 mg/L), sulfate spectrometric chelation-extraction method, pro­ (9,000 mg/L), chloride (15,000 mg/L), iron viding the interference limits discussed in that (4X106 /ig/L), and cadmium, nickel, copper, method are not exceeded. zinc, lead, and chromium (10,000 ptg/L) do not 1.2 Suspended recoverable cobalt is interfere. Higher concentrations of each constit­ calculated by subtracting dissolved cobalt from uent were not investigated. total recoverable cobalt. 1.3 This method may be used to analyze bot­ 4. Apparatus tom material containing at least 5 jig/g of 4.1 Atomic absorption spectrometer cobalt. equipped with electronic digital readout and 1.4 Total recoverable cobalt in water- automatic zero and concentration controls. suspended sediment needs to undergo 4.2 Refer to the manufacturer's manual to preliminary digestion-solubilization by method optimize instrument for the following: 1-3485, and recoverable cobalt in bottom Grating ———————— Ultraviolet material needs to undergo preliminary diges­ Wavelength ————— 240.7 nm tion-solubilization by method 1-5485 before be­ Source (hollow-cathode ing determined. lamp) ——————— Cobalt Oxidant ———————— Air 2. Summary of method Fuel —————————— Acetylene Cobalt is determined by atomic absorption Type of flame ———— Oxidizing spectrometry by direct aspiration of the sam­ 4.3 The Perkin-Elmer, flathead, single-slot ple into an air-acetylene flame without addi­ burner allows a working range of 50 to 1,000 tional treatment of the sample other than the /ig/L. Different burners may be used according addition of ammonium chloride to mask certain to manufacturers1 instructions. interferences. 5. Reagents 3* Interferences 5.1 Ammonium chloride solution, 200 g/L: 3.1 Nitrate at 1 mg/L interferes by suppress­ Dissolve 200 g NH4C1 in demineralized water ing the absorption of the cobalt This interference and dilute to 1 L with demineralized water. 181 182 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Cobalt standard solution /, 1.00 mL= determine the micrograms per liter of cobalt in 100 /ig Co: Dissolve 0.1407 g Co2O3 in a mini* each sample as in paragraph 7.1; then mum amount of dilute HNO3. Add 10 mL concentrated HNO3 (sp gr 1.41) and dilute to mL of original digest 1000 mL with demineralized water. /*g/L Co X _____1,000____ 5.3 Cobalt standard solution II, 1.00 mL= Co (/ig/g) = 10 (Jig Co: Dilute 100.0 mT. cobalt standard solu­ wt of sample (g) tion I and 1 mL concentrated HNO3 (sp gr 1.41) to 1,000 mL with demineralized water. 8. Report 5.4 Cobalt standard working solutions: 8.1 Report cobalt, dissolved (01035), total- Prepare a series of at least six standard work­ recoverable (01037), and suspended-recoverable ing solutions containing from 50 to 1,000 /*g/L (01036), concentrations to the nearest 50 /*g/L. cobalt by appropriate dilution of cobalt stand­ 8.2 Report cobalt, recoverable-from-bottom- ard solution II with acidified water. Add 1.0 mL material (01038), concentrations as follows: 50 NH4C1 solution for each 10 mL standard work­ to 100 /ig/g, the nearest 10 /ig/g; 100 /ig/g and ing solution. Similarly, prepare an acidified above, two significant figures. water blank. Prepare fresh daily. 5.5 Water, acidified: Add 1.5 mL concen­ 9. Precision trated HNO3 (sp gr 1.41) to a liter of deminer­ 9.1 The standard deviation for dissolved alized water. cobalt within the range of 6.2 to 19.3 /ig/L (NOTE 1) for six samples was found to be in­ 6. Procedure dependent of concentration. The 95-percent con­ 6.1 Add 1.0 mL NH4C1 solution to 10.0 mL fidence interval for the average standard sample solution and mix thoroughly. deviation of 4.4 /ig/L ranged from 3.4 to 6.4 6.2 Aspirate the blank to set the automatic Mg/L. zero control. Use the automatic concentration NOTE 1. Precision data for cobalt are below control to set concentrations of standards. Use the reporting level of 50 /ig/L. Samples that con­ at least six standards. Calibrate the instrument tained greater cobalt concentrations were not each time a set of samples is analyzed and check available; however, precision should improve at calibration at reasonable intervals. greater concentrations. 9.2 Precision for dissolved cobalt for three 7. Calculations of the six samples expressed in terms of the 7.1 Determine the micrograms per liter of percent relative standard deviation is as dissolved or total recoverable cobalt in each follows: sample from the digital display or printer while Number of Mean Relative standard deviation aspirating each sample. Dilute those samples laboratories _____(percent)_____ containing cobalt concentrations that exceed 5 6.2 57 the working range of the method and multiply 4 15,8 27 by the proper dilution factors. 3 19.3 11 7.2 To determine micrograms per liter suspended recoverable cobalt, subtract dis- 9.3 It is estimated that the percent relative solved-cobalt concentration from total-recover­ standard deviation for total recoverable and able-cobalt concentration. suspended recoverable cobalt and for recover­ 7.3 To determine micrograms per gram of able cobalt in bottom material will be greater cobalt in bottom-material samples, first than that reported for dissolved cobalt. Cobalt, atomic absorption spectrometric, graphite furnace

Parameter and Code: Cobalt, dissolved, 1-1241-85 0*g/L as Co): 01035

1. Application Calcium (60 mg/L), magnesium (14 mg/L), 1.1 This method may be used to determine sodium (55 mg/L), sulfate (110 mg/L), and chlor­ cobalt in low ionic-strength water and precipita­ ide (45 mg/L) do not interfere. Higher concen­ tion. With deuterium background correction trations of these constituents were not and a 20-/iL sample, the method is applicable investigated. in the range from 0.5 to 100 /ig/L- With Zeeman 3.2 Precipitation samples usually contain background correction and a 20-/*L sample, the very low concentrations of cobalt. Special pre­ method is applicable in the range from 0.5 to cautionary measures must be employed during 65 /ig/L. Sample solutions that contain cobalt both sample collection and laboratory deter­ concentrations exceeding the upper limits must mination to prevent contamination. be diluted or preferably be analyzed by the atomic absorption spectrometric direct or 4. Apparatus chelation-extraction method, or by the atomic 4.1 Atomic absorption spectrometer, for use emission spectrometric ICP method. at 240.7 nm and equipped with background cor­ 1.2 The analytical range and detection limits rection, digital integrator to quantitate peak can be increased or possibly decreased by vary­ areas, graphite furnace with temperature pro­ ing the volume of sample injected or the in­ grammer, and automatic sample injector. The strumental settings. Purification of reagents programmer must have high temperature ramp­ and use of ASTM Type 1 water (Method ing and stopped-flow capabilities. D-1193, American Society for Testing and 4.1.1 Refer to the manufacturer's manual to Materials, 1984) may result in lower detection optimize instrumental performance. The limits. analytical ranges reported in paragraph 1.1 are for a 20-/iL sample JNOTE 1). 2. Summary of method NOTE 1. A 20-/tL sample generally requires 30 Cobalt is determined by atomic absorption s to dry. Samples that have a complex matrix spectrometry in conjunction with a graphite may require a longer drying and charring time. furnace containing a graphite platform 4.1.2 Graphite furnace, capable of reaching (Hinderberger and others, 1981). A sample is temperatures sufficient to atomize the element placed on the graphite platform, then of interest. Warning: dial settings frequently evaporated to dryness, charred, and atomized are inaccurate and newly conditioned furnaces using high-temperature ramping. The absorp­ require temperature calibration. tion signal generated during atomization is 4.1.3 Graphite tubes and platforms. recorded and compared with standards. Pyrolytically coated graphite tubes and solid pyrolytic graphite platforms are recommended. 3. Interferences 4.2 Labware. Many trace metals at very low 3.1 Interferences in low ionic-strength sam­ concentrations have been found to sorb very ples, such as precipitation, normally are quite rapidly to glassware. To preclude this, fluori- low. In addition, the use of the graphite plat­ nated ethylene propylene (FEP) or Teflon lab- form reduces the effects of many interferences. ware may be used. Alternately, glassware, 183 184 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS particularly flasks and pipets, may be treated 5.6 Water, acidified, Type 1: Add 1.5 mL with silicone anti-wetting agent such as Surfacil high-purity, concentrated HNO3(sp gr 1.41) to (Pierce Chemical Co., Rockford, IL, 61105) ac­ each liter of water. cording to the manufacturer's instructions. 5.7 Water, Type 1. Autosampler cups must be checked for con­ tamination. Lancer (1831 Olive St., St. Louis, 6. Procedure MO, 63103) polystyrene disposable cups have 6.1 Systematically clean and rinse work been found to be satisfactory after acid rinsing. areas with deionized water on a regular Alternately, reuseable Teflon or FEP cups may schedule. Use a laminar flow hood or a "clean be used. room" environment during sample transfers. 4.3 Argon, standard, welder's grade, commer­ Ideally, the autosampler and the graphite fur­ cially available Nitrogen may also be used if nace should be in a clean environment. recommended by the instrument manufacturer. 6.2 Soak autosampler cups at least overnight in a 1+1 solution of Type 1 water and high-purity 5. Reagents nitric acid. 5.1 Cobalt standard solution I, 1.00 mL= 6.3 Rinse the sample cups twice with sample 1,000 jig Co: Dissolve 1.4070 g Co2O3 in a min­ before filling. Place cups in sample tray and cover. imum of dilute HNO3. Heat to increase rate of Adjust sampler so that only the injection tip con­ dissolution. Add 10 mL high-purity, concen­ tacts the sample. trated HNO3 (sp gr 1.41), Ultrex or equivalent, 6.4 In sequence; inject 20-/*L aliquots of blank and dilute to 1,000 mL with Type 1 water. and working standards and analyza Analyze 5.2 Cobalt standard solution II, 1.00 mL= the blank and working standards twice Con­ 10.0 Mg Co: Dilute 10.0 mL cobalt standard solu­ struct the analytical curve from the integrated tion I to 1,000 mL (NOTE 2). peak areas (absorbance-seconds). Generally, the NOTE 2. Use acidified Type 1 water curve should be linear to a peak-absorbance (paragraph 5.6) to make dilutions. All standards (peak-height) value of 0.40 absorbance units. must be stored in sealed Teflon or FEP con­ 6.5 Similarly, inject and analyze the samples tainers. Each container must be rinsed twice twice Every tenth sample cup should contain with a small volume of standard before being either a standard or a reference material. filled. Standards stored for 6 months in FEP 6.6 Restandardize as required. Minor containers yielded values equal to those of changes of values for known samples usually in­ freshly prepared standards. dicate deterioration of the furnace tube; contact 5.3 Cobalt standard solution III, 1.00 mL= rings, and (or) platform. A major variation 1.00 fig Co: Dilute 100.0 mL cobalt standard usually indicates either autosampler malfunc­ solution II to 1,000 mL. This standard is used tion or residue buildup from a complex matrix to prepare working standards serially at time in a previous sample of analysis. 5.4 Cobalt standard solution IV, 1.00 7. Calculations mL=0.010 /ig Co: Dilute 10.0 mL cobalt stand­ Determine the micrograms per liter of cobalt ard solution III to 1,000 mL. This standard also in each sample from the digital display or is used to prepare working standards serially printer output. Dilute those samples containing at time of analysis. concentrations of cobalt that exceed the work­ 5.5 Nitric acid, concentrated, high-purity, ing range of the method; repeat the analysis, and (sp gr 1.41): J. T. Baker "Ultrex" brand HNO3 multiply by the proper dilution factors. has been found to be adequately pure; however, each lot must be checked for contamination. 8. Report Analyze acidified Type 1 water for cobalt. Add Report cobalt, dissolved (01035), concentra­ an additional 1.5 mL of concentrated HNO3/ tions as follows: less than 10.0 /ig/L, nearest 0.1 liter of water, and repeat analysis. Integrated jig/L; 10 figlL and above, two significant figures signal should not increase by more than 0.001 for both deuterium background correction and absorbance-seconds. Zeeman background correction. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 185

«/• M. *. \s\fAOM.\JH Relative 9.1 Analysis of one sample 13 times each by Amount Amount Standard standard added found deviation deviation Recovery a single operator using deuterium background (pg/L) 0*g/L) G

Mean Standard deviation Relative standard deviation 8.5 8.61 0.97 11.3 101 G*g/L) (nQlL) (percent) 9.5 10.96 .58 5.3 115 15 14.34 .70 4.9 96 9.05 0.67 7.4 17 17.25 1.42 8.2 101 30 29.03 2.76 9.5 97 9.2 Analysis of four samples six times each Tap water by a single operator using Zeeman background 8.5 8.27 0.85 10.3 97 correction is as follows: 9.5 10.89 .86 7.9 115 15 15.12 1.73 11.7 101 17 15.88 .49 3.1 93 Mean Standard deviation Relative standard deviation 30 28.43 2.68 9.4 95 G*g/L) ^g/L) (percent) 5.75 0.24 4.2 20.52 .26 1.3 9.5 The standard deviation from in- 32.27 .38 1.2 terlaboratory data, without regard to type of 64.20 .20 .3 background correction and use of matrix modifiers, if any, for dissolved cobalt within the 9.3 The precision and bias for the Zeeman range of 2.3 to 18.3 jxg/L for 14 samples, was background correction were tested on deionized found to be independent of concentration. The water and tap water (specific conductance 280 95-percent confidence interval for the average jiS/cm). A known amount of cobalt was added standard deviation of 3.2 jig/L ranged from 2.7 to each sample, and single-operator precision to 3.8 Mg/L- and bias for six replicates are as follows: References Relative Amount Amount Standard standard American Society for Testing and Materials, 1984, Annual added found deviation deviation Recovery book of ASTM standards, section 11, water: Philadel­ 0*g/L) 0*g/L) o*g/i_) (percent) (percent) phia, v. 11.01, p. 39-41. Deionized water Cooksey, M., and Barnett, W. B., 1979, Matrix modifica­ tion and the method of additions in flameless atomic 8.5 8.67 0.88 10.1 102 absorption: Atomic Absorption Newsletter, v. 18, 9.5 9.92 .97 9.8 104 p. 101-5. 15 15.00 1.10 7.3 100 17 17.00 1.52 8.9 100 Fernandez, F. J., Beatty, M. M., and Barnett, W. B., 1981, 30 29.50 1.41 4.8 98 Use of the L'vov platform for furnace atomic absorp­ Tap water tion applications: Atomic Spectroscopy, v. 2, p. 16-21. Hinderberger, E. J.f Kaiser, M. L., and Koirtyohann, S. R., 8.5 8.58 1.07 12.5 101 1981, Furnace atomic absorption analysis of biological 9.5 9.58 .58 6.1 101 samples using the L'vov platform and matrix modifica­ 15 14.92 1.36 9.1 99 tion: Atomic Spectroscopy, v. 2, p. 1-11. 17 16.67 1.66 10.0 98 Manning, D. C., and Slavin, W., 1983, The determination 30 28.33 1.99 7.0 94 of trace elements in natural waters using the stabilized temperature platform furnace: Applied Spectroscopy, v. 37, p. 1-11. 9.4 The precision and bias for the deuterium Ottaway, J. M.t 1982, A revolutionary development in background method were tested on deionized graphite furnace atomic absorption: Atomic Spec­ water and tap water (specific conductance 280 troscopy, v. 3, p. 89-92. Slavin, W.f Carnrick, G. R., and Manning, D. C.f 1982, /iS/cm). A known amount of cobalt was added Magnesium nitrate as a matrix modifier in the stabilized to each sample, and single-operator precision temperature platform furnace: Analytical Chemistry, and bias for six replicates are as follows: v. 54, p. 621-4.

Cobalt, atomic emission spectrometric, ICP

Parameter and Code: Cobalt, dissolved, 1-1472-85 (jig/L as Co): 01035

2. Summary of method method utilizing an induction-coupled argon Cobalt is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 187

Cobalt, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Cobalt, total, 1-5474-85 (mg/kg as Co): none assigned

2. Summary of method hotplate at 200 °C. Cobalt is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec- homogenized. The sample is digested with a trometry. See method 1-5474, metals, major combination of nitric, hydrofluoric, and per­ and minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a spectrometric, direct. 189

Color, electrometric, visual comparison

Parameter and Code: Color, 1-1250-85 (platinum-cobalt units): 00080

1. Application absorption on the sediments or on the filter This method may be used to measure the col­ medium. Centrifuging is preferable to filtration, or of water whose color reasonably matches but centrifuging may not be completely effec­ from 1 to 70 units of the Hazen scale (Hazen, tive in removing very finely divided particles. 1892) and that contains no excessive amount of Flocculation of the dispersed particles with a sediment. Samples that have a color unit value strong electrolyte has been proposed (Lamar, greater than 70 must first be diluted. 1949) and is sometimes effective. The process of flocculation decolorizes some waters and is, 2. Summary of method therefore, not suitable in all cases. The color of the water is compared to that of colored glass disks that have been calibrated to 4. Apparatus correspond to the platinum-cobalt scale of Color comparator, with standard color disks, Hazen (1892). The unit of color is that produced covering the range 0 to 70 color units. by 1 mg/L of platinum. A small amount of cobalt may be added to aid in color matching. 5. Reagents The Hazen scale (platinum-cobalt units) is usual­ None required. ly satisfactory for most waters, but the hues and shades of some waters may not easily be 6. Procedure compared with standards. If the hue of the 6.1 Fill one instrument tube with the sam­ water does not compare with that of the stand­ ple of water, level the tube, insert the glass plug, ard, very little can be done except to visually making sure that no air bubbles are trapped, compare the absorbances of the sample and and insert the tube into the comparator. standard. Highly colored waters should not be 6.2 Use demineralized water as a blank in diluted more than necessary because the color the second tube. of the diluted sample often is not proportional 6.3 The color comparison is made by revolv­ to the dilution. ing the disk until the colors of the two tubes match. Samples having color values greater 3. Interferences than 70 must first be diluted. Turbidity generally causes the observed col­ or value to be greater than the true color value, 7. Calculations but there is some disagreement as to the Read the color directly from the matching col­ magnitude of the effect of turbidity. The or standard; apply the proper dilution if re­ removal of turbidity is a recurrent problem in quired. the determination of color. Color is removed by absorption on suspended material. Filtration 8. Report of samples to remove turbidity frequently re­ Report color (00080) (platinum-cobalt units) moves some of the color-imparting solutes by as follows:

191 192 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Color unit Record units to nearest References 1-49 1 50-99 5 Hazen, Alien, 1892, A new color standard for natural 100-249 10 250-500 20 waters: American Chemical Society Journal, v. 12, p. 427. 9. Precision Lamar, W.L., 1949, Determination of color of turbid waters: Precision data are not available for this method. Analytical Chemistry, v. 21, p. 726-27. Copper, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Copper, dissolved, 1-1271-85 (pglL as Cu): 01040 Copper, total recoverable, 1-3271-85 fcig/L as Cu): 01042 Copper, suspended recoverable, 1-7271-85 (ftg/L as Cu): 01041

1. Application 4.2 Refer to the manufacturer's manual to 1.1 This method may be used to analyze optimize instrument for the following: water and water-suspended sediment contain­ Grating ———————— Ultraviolet ing from 1 to 50 /*g/L of copper. Sample solu­ Wavelength ————— 324.7 nm tions containing more than 50 jtg/L need either Source (hollow-cathode to be diluted prior to chelation-extraction or to lamp) ——————— Copper be analyzed by the atomic absorption spec­ Oxidant ———————— Air trometric direct method. Fuel —————————— Acetylene 1.2 Suspended recoverable copper is Type of flame ———— Oxidizing calculated by subtracting dissolved copper from 4.3 Different burners may be used according total recoverable copper. to manufacturers' instructions. 1.3 Total recoverable copper in water-sus­ pended sediment needs to undergo a prelimi­ 5. Reagents nary digestion-solubilization by method 1-3485 5.1 Ammonium pyrrolidine dithiocarbamate before being determined. solution, 1 g/100 mL: Dissolve 1 g APDC in 100 1.4 If the iron concentration of the sample mL demineralized water. Prepare fresh daily. exceeds 25,000 /tg/L, determine copper by 5.2 Citric acid-sodium citrate buffer solution: the atomic absorption spectrometric direct Dissolve 126 g citric acid monohydrate and 44 method. g sodium citrate dihydrate in demineralized water and dilute to 1 L with demineralized 2. Summary of method water. See NOTE 3 before preparation. Copper is determined by atomic absorption 5.3 Copper standard solution /, 1.00 spectrometry following chelation with am­ mL=100 fig Cu: Dissolve 0.1252 g CuO in a min­ monium pyrrolidine dithiocarbamate (APDC) imum amount of dilute HNO3. Heat to increase and extraction with methyl isobutyl ketone rate of dissolution. Add 10.0 mL concentrated (MIBK). The extract is aspirated into an air- HNO3 (sp gr 1.41) and dilute to 1,000 mL with acetylene flame of the spectrometer. demineralized water. 5.4 Copper standard solution II, 1.00 3. Interferences mL=1.00 fig Cu: Dilute 10.0 mL copper stand­ Concentrations of iron greater than 25,000 ard solution I and 1 mL concentrated HNO3 (sp jtg/L interfere by suppressing the copper ab­ gr 1.41) to 1,000 mL with demineralized water. sorption. This standard is used to prepare working stand­ ards at the time of analysis. 4. Apparatus 5.5 Methyl isobutyl ketone (MIBK). 4.1 Atomic absorption spectrometer 5.6 Potassium hydroxide, 10M: Dissolve 56 equipped with electronic digital readout and g KOH in demineralized water, cool, and dilute automatic zero and concentration controls. to 100 mL. 193 194 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.7 Potassium hydroxide, 2.5M: Dissolve 14 7. Calculations g KOH in demineralized water and dilute to 100 7.1 Determine the micrograms per liter of mL (NOTE 1). dissolved or total recoverable copper in each NOTE 1. Alternatively, a 2.5M NH4OH solu­ sample from the digital display or printer. tion may be used. Add 167 mL concentrated Dilute those samples containing copper concen­ NH4OH (sp gr 0.90) to 600 mL demineralized trations that exceed the working range of the water. Cool, and dilute to 1 L. method; repeat the chelation-extraction, and 5.8 Water, acidified: Add 1.5 mL concen­ multiply by the proper dilution factors. trated HNO3 (sp gr 1.41) to 1 L of demineral­ 7.2 To determine the micrograms per liter of ized water. suspended recoverable copper, subtract dis- solved-copper concentration from total- 6. Procedure recoverable-copper concentration. 6.1 Clean all glassware used in this deter­ mination with warm, dilute HNO3 (1+9) and 8. Report rinse with demineralized water immediately Report copper, dissolved (01040), total- before use. recoverable (01042), and suspended-recoverable 6.2 Pipet a volume of sample solution con­ (01041), concentrations as follows: less than 10 taining less than 5.0 tig Cu (100 mL max) into Mg/L, nearest microgram per liter; 10 jig/L and a 200-mL volumetric flask and adjust the above, two significant figures. volume to approx 100 mL. 6.3 Prepare a blank with 1.5 mL concen­ 9. Precision trated HNO3 per liter of acidified water and 9.1 Precision for dissolved copper for eight sufficient standards, and adjust the volume of samples within the range of 18.5 to 403 jig/L each to approx 100 mL with acidified water. may be expressed as follows: 6.4 With a pH meter, adjust the pH of each solution to 2.4 with 2.5AT KOH (NOTE 2 and NOTE 3). Shake for 3 min. 0.084X + 2.57 NOTE 2. For water-suspended sediment sam­ ples that have been digested, add 1 to 2 mL 10M KOH or concentrated NH4OH (sp gr 0.90) where before pH adjustment. ST= overall precision, micrograms per liter, NOTE 3. If an automated titration system is and used to adjust the pH, add 2.5 mL citric acid- X— concentration of copper, micrograms per sodium citrate buffer solution prior to pH ad­ liter. justment. This will prevent over- shooting the The correlation coefficient is 0.8156. end point in poorly buffered samples. 9.2 Precision for dissolved copper for four of 6.5 Add 2.5 mL APDC solution and mix. the eight samples expressed in terms of the per­ 6.6 Add 10.0 mL MIBK and shake vigorous­ cent relative standard deviation is as follows: ly for 3 min. 6.7 Allow the layers to separate and add Number of Mean Relative standard deviation demineralized water until the ketone layer is laboratories _____(percent)_____ completely in the neck of the flask. 4 18.5 14 6.8 Aspirate the ketone layer within 1 h. 3 100 0 3 153 21 Aspirate the ketone layer of the blank to set the 3 403 8 automatic zero control. Use the automatic con­ centration control to set the concentrations of standards. Use at least six standards. Calibrate 9.3 It is estimated that the percent relative the instrument each time a set of samples is standard deviation for total-recoverable and analyzed and check calibration at reasonable in­ suspended recoverable copper will be greater tervals. than that reported for dissolved copper. Copper, atomic absorption spectrometric, direct

Parameters and Codes: Copper, dissolved, 1-1270-85 (/tg/L as Cu): 01040 Copper, total recoverable, I-3270-85 (/ig/L as Cu): 01042 Copper, suspended recoverable, I-7270-85 (jtg/L as Cu): 01041 Copper, recoverable-from-bottom-material, dry wt, I-5270-85 (jig/g as Cu): 01043

1. Application mg/L), magnesium (4,000 mg/L), sulfate (9,000 1.1 This method may be used to analyze water mg/L), chloride (9,000 mg/L), nitrate (2,000 and water-suspended sediment containing at mg/L), iron (4X106/ig/L), lead, cadmium, zinc, least 10 /ig/L of copper. Sample solutions con­ and chromium (10,000 /tg/L each) do not in­ taining more than 1,000 /*g/L need either to be terfere. Higher concentrations of each constit­ diluted or to be read on a less expanded scale. uent were not investigated. Nickel and cobalt Brines need to be analyzed by the atomic ab­ concentrations greater than 8,000 jig/L sup­ sorption spectrometric chelation-extraction press the copper absorption. method, providing that the interference limits discussed in that method are not exceeded. 4. Apparatus 1.2 Suspended recoverable copper is calcu­ 4.1 Atomic absorption spectrometer lated by subtracting dissolved copper from total equipped with electronic digital readout and recoverable copper. automatic zero and concentration controls. 1.3 This method may be used to analyze bot­ 4.2 Refer to the manufacturer's manual to tom material containing at least 1 /ig/g of cop­ optimize instrument for the following: per. Prepared sample solutions containing more Grating ——————— Ultraviolet than 1,000 jig/L need either to be diluted or to Wavelength ————— 324.7 nm be read on a less expanded scale. Source (hollow-cathode 1.4 Total recoverable copper in water-sus­ lamp) ———————— Copper pended sediment needs to undergo preliminary Oxidant ———————— Air digestion-solubilization by method 1-3485, and Fuel —————————— Acetylene recoverable copper in bottom material needs to Type of flame ———— Oxidizing undergo preliminary digestion-solubilization by 4.3 The 100-mm (4-in.), flathead, single-slot method 1-5485 before being determined. burner allows a working range of 10 to 1,000 jig/L. Different burners may be used according 2. Summary of method to manufacturers' instructions. 2.1 Copper is determined by atomic absorp­ tion spectrometry by direct aspiration of the 5. Reagents sample solution into an air-acetylene flame 5.1 Copper standard solution /, 1.00 mL= (Fishman and Downs, 1966). 1000 jig Cu: Dissolve 1.252 g CuO in a minimum 2.2 The procedure may be automated by the amount of dilute HNO3. Heat to increase rate addition of a sampler and either a strip-chart of dissolution. Add 10.0 mL concentrated recorder or a printer or both. HNO3 (sp gr 1.41) and dilute to 1000 mL with demineralized water. 3. Interferences 5.2 Copper standard solution //, 1.00 mL= Individual concentrations of sodium (9,000 5.00 /*g Cu: Dilute 5.0 mL copper standard solu­ mg/L), potassium (9,000 mg/L), calcium (4,000 tion I and 1 mL concentrated HNO3 (sp gr 1.41) 195 196 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS to 1,000 mL with demineralized water. This 8.2 Report copper, recoverable-from-bottom- standard is used to prepare working standards material (01043), concentrations as follows: less at time of analysis. than 10 /ig/g, nearest microgram per gram; 10 5.3 Copper working standards: Prepare a /ig/g and above, two significant figures. series of at least six working standards contain­ ing from 10 to 1,000 fig/L of copper by ap­ 9. Precision propriate dilution of copper standard solution 9.1 Precision for dissolved copper for 28 II with acidified water. Prepare fresh daily. samples within the range of 10 to 595 pg/L may 5.4 Water, acidified: Add 1.5 mL concen­ be expressed as follows: trated HNO3 (sp gr 1.41) to 1 L of demineral­ ized water. ST = 0.057X + 7.13 6. Procedure Aspirate the blank (acidified water) to set the where automatic zero control. Use the automatic con­ ST= overall precision, micrograms per liter, centration control to set the concentrations of and standards. Use at least six standards. Calibrate X= concentration of copper, micrograms per the instrument each time a set of samples is liter. analyzed and check calibration at reasonable in­ The correlation coefficient is 0.8007. tervals. 9.2 Precision for dissolved copper for five of the 28 samples expressed in terms of the per­ 7. Calculations cent relative standard deviation is as follows: 7.1 Determine the micrograms per liter of Number of Mean Relative standard deviation dissolved or total recoverable copper in each laboratories 0*0/1) _____(percent)_____ sample solution from the digital display or 9 10.0 90 printer while aspirating each sample. Dilute 30 60.3 14 22 100 16 those samples containing copper concentrations 28 245 11 that exceed the working range of the method 23 595 9 and multiply by proper dilution factors. 7.2 To determine micrograms per liter 9.3 It is estimated that the percent relative suspended recoverable copper, subtract dis- standard deviation for total recoverable and solved-copper concentration from total- suspended recoverable copper and for recov­ recoverable-copper concentration. erable copper in bottom material will be greater 7.3 To determine the micrograms per gram than that reported for dissolved copper. of copper in bottom-material samples, first 9.4 Precision for total recoverable copper ex­ determine the micrograms per liter of copper in pressed in terms of percent relative standard each sample as in paragraph 7.1; then deviation for two water-suspended sediment mixtures is as follows:

mL of original digest Number of Relative standard deviation Cu X laboratories (Mfl/L) _____(percent)______1,000 CU (fJLglg) = 17 21.1 39 wt of sample (g) 23 131 16

8. Report 8.1 Report copper, dissolved (01040), total- References recoverable (01042), and suspended- recoverable Fishman, M. J., and Downs, S. C., 1966, Methods for (01041), concentrations as follows: less than 100 analysis of selected metals in water by atomic absorp­ /ig/L, nearest 10 ^g/L; 100 /ig/L and above, two tion: U.S. Geological Survey Water-Supply Paper significant figures. 1540-C, p. 28-30. Copper, atomic absorption spectrometric, graphite furnace

Parameter and Code: Copper, dissolved, 1-1272-85 (MQ/L as Cu): 01040

1* Application Calcium (60 mg/L), magnesium (10 mg/L), 1.1 This method may be used to determine sodium (50 mg/L), sulfate (100 mg/L), and copper in low ionic-strength water and precipita­ chloride (40 mg/L) do not interfere. Higher con­ tion. With deuterium background correction centrations of these constituents were not in­ and a 20-/*L sample, the method is applicable vestigated. in the range from 0.2 to 10 /xg/L. With Zeeman 3.2 Precipitation samples usually contain background correction and a 20-/xL sample, the very low concentrations of copper. Special method is applicable in the range from 0.5 to precautionary measures must be employed dur­ 35 /*g/L. Sample solutions that contain copper ing both sample collection and laboratory deter­ concentrations exceeding the upper limits must mination to prevent contamination. be diluted or preferably be analyzed by the atomic absorption spectrometric direct or chela- 4. Apparatus tion-extraction method, or by the atomic emis­ 4.1 Atomic absorption spectrometer, for use sion spectrometric ICP method. at 324.7 nm and equipped with background cor­ 1.2 The analytical range and detection limits rection, digital integrator to quantitate peak can be increased or possibly decreased by vary­ areas, graphite furnace with temperature pro­ ing the volume of sample injected or the in­ grammer, and automatic sample injector. The strumental settings. Purification of reagents programmer must have high-temperature ramp­ and use of ASTM Type 1 water (Method ing and stopped-flow capabilities. D-1193, American Society for Testing and 4.1.1 Refer to the manufacturer's manual to Materials, 1984) may result in lower detection optimize instrumental performance. The limits. analytical ranges reported in paragraph 1.1 are for a 20-ftL sample (NOTE 1). 2. Summary of method NOTE 1. A 20-jiL sample generally requires 30 Copper is determined by atomic absorption s to dry. Samples that have a complex matrix spectrometry in conjunction with a graphite fur­ may require a longer drying and charring time. nace containing a graphite platform (Hinder- 4.1.2 Graphite furnace, capable of reaching berger and others, 1981). A sample is placed on temperatures sufficient to atomize the element the graphite platform, and the sample is then of interest. Warning: dial settings frequently evaporated to dryness, charred, and atomized are inaccurate and newly conditioned furnaces using high-temperature ramping. The absorp­ require temperature calibration. tion signal generated during atomization is 4.1.3 Graphite tubes and platforms. Pyro- recorded and compared with standards. lytically coated graphite tubes and solid pyrolytic graphite platforms are recommended. 3. Interferences 4.2 Lab ware. Many trace metals at very low 3.1 Interferences in low ionic-strength sam­ concentrations have been found to sorb very ples, such as precipitation, normally are quite rapidly to glassware. To preclude this, fluori- low. In addition, the use of the graphite plat­ nated ethylene propylene (FEP) or Teflon lab- form reduces the effects of many interferences. ware may be used. Alternately, glassware, 197 198 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS particularly flasks and pipets, may be treated 5.6 Water, acidified, Type 1: Add 1.5 mL with silicone anti-wetting agent such as Surfacil high-purity, concentrated HNO3 (sp gr 1.41) to (Pierce Chemical Ca, Rockford, IL, 61105) accord­ each liter of water. ing to the manufacturer's instructions. Autosam- 5.7 Water, Type L pler cups must be checked for contamination. Lancer (1831 Olive St., St. Louis, MO, 63103) 6. Procedure polystyrene disposable cups have been found to 6.1 Systematically clean and rinse work be satisfactory after acid rinsing. Alternately, areas with deionized water on a regular reuseable Tbflon or FEP cups may be used. schedule. Use a laminar flow hood or a "clean room" environment during sample transfers. 4.3 Argon, standard, welder's grade, commer­ Ideally, the autosampler and the graphite fur­ cially available. Nitrogen may also be used if nace should be in a clean environment. recommended by the instrument manufacturer. 6.2 Soak autosampler cups at least over­ night in a 1+1 solution of Type 1 water and 5. Reagents high-purity nitric acid. 5.1 Copper standard solution /, 1.00 mL= 6.3 Rinse the sample cups twice with sam­ 1,000 jig Cu: Dissolve 1.2518 g CuO in a mini­ ple before filling. Place cups in sample tray and mum of dilute HNO3. Heat to increase rate of cover. Adjust sampler so that only the injection dissolution. Add 10 mL high-purity, concen­ tip contacts the sample. trated HNO3 (sp gr 1.41) Ultrex or equivalent 6.4 In sequence, inject 20-/*L aliquots of blank and dilute to 1,000 mL with Type 1 water. and working standards, and analyze Analyze the 5.2 Copper standard solution II, 1.00 mL= blank and working standards twice. Construct 10.0 jig Cu: Dilute 10.0 mL copper standard the analytical curve from the integrated peak solution I to 1,000 mL (NOTE 2). areas (absorbance-seconds). Generally, the curve NOTE 2. Use acidified Type 1 water (para­ should be linear to a peak-absorbance (peak- graph 5.6) to make dilutions. All standards height) value of 0.40 absorbance units. must be stored in sealed Teflon or FEP con­ 6.5 Similarly, inject and analyze the samples tainers. Each container must be rinsed twice twice. Every tenth sample cup should contain with a small volume of standard before being either a standard or a reference material. filled. Standards stored for 6 months in FEP 6.6 Restandardize as required. Minor containers yielded values equal to those of changes of values for known samples usually in­ freshly prepared standards. dicate deterioration of the furnace tube, contact 5.3 Copper standard solution III, 1.00 mL= rings, and (or) platform. A major variation 1.00 fig Cu: Dilute 100.0 mL copper standard usually indicates either autosampler malfunc­ solution II to 1,000 mL. This standard is used tion or residue buildup from a complex matrix to prepare working standards serially at time in a previous sample. of analysis. 5.4 Copper standard solution IV, 1.00 mL= 7* Calculations 0.010 pig Cu: Dilute 10.0 mL copper standard Determine the micrograms per liter of copper solution III to 1,000 mL. This standard also is in each sample from the digital display or used to prepare working standards serially at printer output. Dilute those samples containing time of analysis. concentrations of copper that exceed the work­ 5.5 Nitric acid, concentrated, high-purity, ing range of the method; repeat the analysis, (sp gr 1.41): J. T. Baker "Ultrex" brand HNO3 and multiply by the proper dilution factors. has been found to be adequately pure; however, each lot must be checked for contamination. 8. Report Analyze acidified Type 1 water for copper. Add Report copper, dissolved (01040), concentra­ an additional 1.5 mL of concentrated HNO3 per tions as follows: less than 10.0 /*g/L, nearest 0.1 liter of water, and repeat analysis. The in­ /ig/L; 10 /ig/L and above, two significant figures tegrated signal should not increase by more for both deuterium background correction and than 0.001 absorbance-seconds. Zeeman background correction. METHODS FOR DETERMINATION OP INORGANIC SUBSTANCES 199 9. Precision 9.4 The precision and bias for the deuterium 9.1 Analysis of six samples six times each background method were tested on deionized by a single operator using deuterium water and tap water (specific conductance 280 background correction is as follows: fjtSlcm). A known amount of copper was added to each sample, and single-operator precision Mean Standard deviation Relative standard deviation and bias for six replicates are as follows: OigfL) <,ig/L) (percent)

0.60 0.04 7.2 Relative 1.38 .11 8.1 Amount Amount Standard standard 2.31 .10 4.2 added found deviation deviation Recovery 4.11 .15 3.6 (M9/L) (MQ/L) fcg/L) (percent) (percent) 5.58 .25 4.4 Deionized water 10.25 .40 3.9 4.35 4.38 0.13 3.0 101 9.2 Analysis of four samples by a single 8.0 7.45 .34 4.6 93 8.7 8.42 .52 6.2 97 operator using Zeeman background correction 9.0 8.68 .57 6.5 96 is as follows: 16 15 .75 5.0 94 Tap water (NOTE 3) Relative standard Number of Mean Standard deviation deviation 4.35 9.40 .72 1.1 216 replicates (pg/L) (pg/L) (percent) 8.0 7.37 2.17 3.5 92 3 3.93 0.55 14 8.7 16.75 1.99 2.8 193 4 12.85 1.23 9.6 9.0 18.83 5.41 12 209 9 17.76 .36 2.0 16 22.88 2.76 3.6 143 6 34.88 1.13 3.2 9.5 Interlaboratory precision for dissolved 9.3 The precision and bias for the Zeeman copper for 12 samples within the range of 21.8 background correction were tested on deionized to 490 pg/L without regard to type of back­ water and tap water (specific conductance 280 ground correction and use of matrix modifiers, piS/cm). A known amount of copper was added if any, may be expressed as follows: to each sample, and single-operator precision and bias for six replicates are as follows: ST =0.184X + 2.04

Relative where Amount Amount Standard standard ST = overall precision, micrograms per liter, added found deviation deviation Recovery (MQ/L) (MQ/L) fcg/L) (percent) (percent) and Deionized water X = concentration of copper, micrograms per 4.35 4.57 0.29 6.3 105 liter. 8.0 8.23 .46 5.6 103 The correlation coefficient is 0.9246. 8.7 9.23 .57 6.2 106 9.0 8.40 .40 4.8 93 16 16.10 .98 6.1 101 References Tap water (NOTE 3) American Society for Testing and Materials, 1984, Annual 4.35 6.45 4.00 7.0 148 book of ASTM standards, section 11, water: Philadel­ 8.0 8.28 3.47 5.9 103 phia, v. 11.01, p. 39-41. 8.7 12.97 4.15 6.6 149 Cooksey, M., and Barnett, W. B., 1979, Matrix modifica­ 9.0 9.49 1.73 5.0 105 16 14.17 4.43 6.9 89 tion and the method of additions in flameless atomic absorption: Atomic Absorption Newsletter, v. 18, p. 101-5. Fernandez, F. J., Beatty, M. M., and Barnett, W. B., 1981, NOTE 3. The tap water contained approx 50 Use of the L'vov platform for furnace atomic absorp­ /ig/L of copper, and the standard deviation and tion applications: Atomic Spectroscopy, v. 2, p. 16-21. Hinderberger, £. J., Kaiser, M. L., and Koirtyohann, S. R., percent relative standard deviation were 1981, Furnace atomic absorption analysis of biological calculated prior to subtraction of copper samples using the LVov platform and matrix modifica­ originally present. tion: Atomic Spectroscopy, v. 2, p. 1-11. 200 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Manning, D. C., and Slavin, W., 1983, The determination graphite furnace atomic absorption: Atomic Spec­ of trace elements in natural waters using the stabiliz­ troscopy, v. 3, p. 89-92. ed temperature platform furnace: Applied Spectroscopy, Slavin, W., Carnrick, G. R., and Manning, D. C., 1982, Mag­ v. 37, p. 1-11. nesium nitrate as a matrix modifier in the stabilized Ottaway, J. M., 1982, A revolutionary development in temperature platform furnace: Analytical Chemistry, v. 54, p. 621-4. Copper, atomic emission spectrometric, ICP

Parameter and Code: Copper, dissolved, 1-1472-85 (pg/L as Cu): 01040

2. Summary of method method utilizing an induction-coupled argon Copper is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 201

Copper, totaMn-sediment, atomic absorption spectrometric, direct

Parameter and Code: Copper, total, 1-5474-85 (mg/kg as Cu): none assigned

2. Summary of method hotplate at 200 °C. Copper is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec- homogenized. The sample is digested with a trometry. See method 1-5474, metals, major combination of nitric, hydrofluoric, and per­ and minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a spectrometric, direct. 203

Cyanide, colorimetric, barbituric acid, automated-segmented flow

Parameters and Codes: Cyanide, dissolved, 1-2302-85 (mg/L as CN): 00723 Cyanide, total recoverable, 1-4302-85 (mg/L as CN): 00720 Cyanide, recoverable-from-bottom-material, dry wt, 1-6302-85 (mg/kg as CN): 00721

1. Application 3.6 Sulfate concentrations of 4,000 mg/L do 1.1 This method may be used to analyze water not interfere. Higher concentrations were not and water-suspended sediment containing from tested. 0.01 to 0.30 mg/L cyanide. Samples containing more than 0.30 mg/L need to be diluted. 4. Apparatus 1.2 Total recoverable cyanide in water- 4.1 Distillation train (fig. 21). An efficient suspended sediment can be determined if each gas washer is essential to the proper operation sample is shaken vigorously and a suitable ali­ of the distillation assembly. The Fisher-Milligan quot of well-mixed sample withdrawn. unit has been found satisfactory. This ap­ 1.3 This method may be used to determine paratus is for use only with bottom materials. cyanide in bottom material containing at least 4.2 Heating element for Claisen flask. 0.5 mg/kg. 4.3 Technicon AutoAnalyzer II, consisting of sampler, cartridge manifold with ultraviolet 2. Summary of method digester, proportioning pump, heating bath This method is based on the chlorination of with distillation head, voltage stabilizer, re­ cyanide with chloramine-T and on the subsequent corder, and printer. reaction with a pyridine-barbituric acid reagent 4.4 With this equipment the following (Goulden and others, 1972). This method detects operating conditions have been found satisfac­ simple cyanides only; therefore, any complex cya­ tory for the range from 0.01 to 0.30 mg/L CN: nides must first be broken down by passing the Absorption cell ——— 15 mm acidified sample solution through an ultraviolet Wavelength ————— 570 nm digestion-distillation procedure. The distillation Cam —————————— 20/h (6/1) step also removes certain interferences. Heating-bath temper­ ature ———————— 155°C 3. Interferences 3.1 Chloride interferes if its concentration 5. Reagents exceeds 3,000 mg/L. 5.1 Chloramine-T solution, 4.0 g/L: Dissolve 3.2 Oxidizing agents may interfere. 2.0 g chloramine-T in demineralized water and 3.3 Glycine and urea at the 10-mg/L level do dilute to 500 mL. not interfere. 5.2 Cyanide standard solution /, 1.00 3.4 A concentration of 10 mg/L sulfide in­ mL = 0.100 mg CN: Dissolve 0.2500 g KCN creases the apparent cyanide concentration by (NOTE 1) in 0.1M NaOH and dilute to 1,000 mL approx 0.02 mg/L. Concentrations of sulfide with 0.1M NaOH. Discard after 3 months. greater than 10 mg/L interfere considerably. NOTE 1. CAUTION-POISON: May be fatal 3.5 Thiocyanate is broken down to cyanide if swallowed or inhaled. Contact with acid and sulfide by this procedure and, therefore, in­ liberates poisonous gas. Contact with KCN may terferes on an equimolar basis. burn eyes and irritate skin. 205 206 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Allihn water-cooled condenser 9-mmOD

Thistle tube

Standard tapered joint — Standard tapered joint SI?^ Screw clamp 500-mt suction flask 500-mL modified Fisher-Milhgan Claisen flask spiral gas washer

Figure 21.—Cyanide, distillation train

5.3 Cyanide standard solution //, 1.00 mT. = demineralized water. Dilute to 1 L with 0.002 mg CN: Add 20 mL cyanide standard demineralized water. solution I to 800 mL O.lM NaOH and dilute to 5.8 Pyridine-barbituric acid solution: Place 1,000 mL with O.lM NaOH. Prepare fresh daily. 15 g barbituric acid in a 1-L beaker and add 5.4 Cyanide working standards: Prepare enough demineralized water (about 100 mL) to fresh daily, a blank and 100 mL each of a series wash the sides of the beaker and wet the bar­ of cyanide working standards by appropriate bituric acid. Add 75 mL pyridine and mix. Add quantitative dilution of cyanide standard solu­ 15 ™TJ concentrated HC1 (sp gr 1.19) and mix. tion II as follows: Dilute to about 900 mL with demineralized water and mi* until all the barbituric acid has Cyanide standard solution II Cyanide concentration dissolved. Transfer the solution to a 1,000-mL (mL) (mg/L) volumetric flask and dilute to volume with 0.020 demineralized water. 2.0 .040 5.0 .100 5.9 Sodium hydroxide, IM: Dissolve 4 g 10.0 .200 NaOH in 100 mL demineralized water. 15.0 .300 5.10 Sulfuric acid, concentrated (sp gr 1.84).

5.5 Magnesium chloride solution, 24 g/100 6. Procedure mL: Dissolve 51 g MgCl2-6H2O in 100 mL 6.1 For water or water-suspended sediment demineralized water. proceed to paragraph 6.2. For bottom material 5.6 Phosphate buffer solution: Dissolve 13.6 proceed as follows: g KH2PO4 and 0.28 g Na2HPO4 in demineral­ 6.1.1 Assemble the distillation train, con­ ized water and dilute to 1L. Add 0.5 mL Brij-35 sisting of Claisen flask, thistle tube, condenser, solution and mix. gas washer, screw damp, suction flask, and 5.7 Phosphoric acid-hypophosphorous acid aspirator (fig. 21). distillation reagent: Carefully add 250 mL 6.1.2 Add a weighed portion (5 to 10 g) of concentrated H3PO4 (sp gr 1.69) and 50 mL bottom-material sample and 250 to 500 mL hypophosphorous acid to approx 700 mL demineralized water to the boiling flask. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 207 6.1.3 Add exactly 50 mL 1M NaOH and 100 be well mixed by vigorous shaking before mTj demineralized water to the gas washer. Con­ transferring a portion to a sample cup. nect train and adjust suction so that 1 or 2 bub­ 6.6 Begin analysis. When the peak from the bles per second enter the boiling flask through most concentrated working standard appears the air inlet. Do not increase airflow beyond 2 on the recorder, adjust the STD control until bubbles per second. the flat portion of the peak reads full scale. 6.1.4 Add 10 mL MgCl2 solution through the thistle tube, and allow the airflow to mix for 3 7. Calculations min. Rinse air tube with demineralized water, 7.1 Prepare an analytical curve by plotting then slowly add 20 mL concentrated H2SO4. the height of each standard peak versus its Rinse the tube again. respective cyanide concentration. 6.1.5 Heat at a rate that provides rapid boil­ 7.2 Compute the concentration of dissolved ing, but not enough to flood the condenser in­ or total recoverable cyanide in milligrams per let or permit the vapors to rise more than liter by comparing each sample peak height halfway into the condenser. Reflux for 1 h. Turn with the analytical curve. Any baseline drift off heat, but permit airflow to continue for 15 that may occur must be taken into account min. when computing the height of a sample or 6.1.6 Transfer gas washer contents to a standard peak. 200-mL volumetric flask. Wash the tube, from 7.3 To determine milligrams per kilogram of the condenser to the gas washer, and the gas cyanide in bottom-material samples, first deter­ washer with small amounts of demineralized mine the milligrams per liter of cyanide in each water and add to contents of flask. Dilute con­ sample as in paragraph 7.2; then: tents of volumetric flask to 200 mL. 6.1.7 Refill the gas washer with NaOH and distmate demineralized water, as in 6.1.3, and repeat CN(mg/kg) = x mg/L CN reflux procedure. If only readily hydrolyzed wt of sample (g) cyanides are present, the absorber liquid from the first reflux period will contain all the available cyanide. If stable complex cyanides 8. Report are present, a measurable yield will appear in 8.1 Report cyanide, dissolved (00723) and the absorber liquid during the second and suc­ total-recoverable (00720), concentrations as ceeding reflux periods, depending on the degree follows: less than 1.00 mg/L, nearest 0.01 mg/L; of stability of the compounds. 1.00 mg/L and above, two significant figures. 6.2 Set up manifold (fig. 22). 8.2 Report cyanide, total-recoverable-in- 6.3 Allow the colorimeter, recorder, and bottom-material (00721), concentrations as heating bath to warm up for 30 min or until the follows: less than 10 mg/kg, nearest 0.1 mg/kg; heating-bath temperature has stabilized at 10 mg/kg and above, two significant figures. 155 °C. Cold water must be flowing through the condensing jacket of the distillation head when 9. Precision heating bath is operating. 9.1 Precision for dissolved cyanide ex­ 6.4 Adjust the baseline to read zero scale pressed in terms of the percent relative stand­ divisions on the recorder with all reagents, but ard deviation for replicate analysis by a single with demineralized water in the sample tube. operator is as follows: 6.5 Place a complete set of standards and a Relative standard deviation blank in the first positions of the first sample _____(percent)_____ tray, beginning with the most concentrated 0.041 2 standard. Place individual standards of differ­ .125 1 ing concentrations in approximately every .224 1 eighth position of the remainder of this and subsequent sample trays. Fill remainder of each 9.2 It is estimated that the percent relative tray with unknown samples. Each sample must standard deviation for total recoverable cyanide 208 TECHNIQUES OP WATER-RESOURCES INVESTIGATIONS

Proportioning pump

Distillation coilil 0.100 in Water 3.40 mL/min n. Heating 0.030 in Air UV digest!>r Coil bath 0.32 mL/min 194-BOO5-02 155«C * 0.073 in Sample 2.00 mL/min Distillation reagent 0 0.035 in 0.42 mL/min Sampler 4 20/h tastee -*•*—— 0.035 in 6/lcam To iwast 9,42 ml/m.jn 1 ** *** * 0.050 Kel-F ** 0.100 Acidflex *** 0.034 Polyethylene e -« —— 0.056 in To wast 1.20 mL/min To waste Air 10- 20- 5- 0.030 in ——— turn coil turn coil turn c oil 0.32 mL/min 4 i— ——ODD —- fl™* mm 0.051 in Resample 1.00 mL/min Buffer Colorimeter 0.035 in Recorder 0.42 mL/min 570nm 15-mm cell 0.051 in Chloramine- 0.10 mL/min Pyridine-ba 0.051 in acid reage 1.00 mL/min 0.051 in To wast i * 1.00 mL/min

Figure 22.—Cyanide, barbituric acid manifold

and for recoverable cyanide in bottom material Determination of nanogram quantities of simple and will be greater than that reported for dissolved complex cyanides in water: Analytical Chemistry, v. 44, cyanide. p. 1845-49. U.S. Environmental Protection Agency, 1979, Methods for References chemical analysis of water and wastes: Cincinnati, p. Goulden, P. D., Afghan, B. K, and Brooksbank, Peter, 1972, 353.3-1. Cyanide, colorimetric, pyridine-pyrazolone

Parameters and Codes: Cyanide, dissolved, 1-1300-85 mg/L as CN): 00723 Cyanide, total, I-3300-85 (mg/L as CN): 00720 Cyanide, total-in-bottom-material, dry wt, I-5300-85 (mg/kg as CN): 00721

1. Application precipitate with demineralized water, and add 1.1 The method may be used to determine the washings to the filtrate. cyanide in water and water-suspended sediment 3.2.2 Fatty acids can be removed by acidify­ containing at least 0.01 mg/L of cyanide. ing 400 mL of sample with acetic acid to a pH 1.2 This method may be used to determine of between 6 and 7, and by extracting with 80 cyanide in bottom material containing at least mL of either isooctane or hexane. A single ex­ 0.5 mg/kg. traction is usually sufficient. 1.3 Total cyanide in water-suspended sedi­ 3.2.3 Oxidizing agents can be removed by ment may be determined if each sample is adding sodium sulfite solution to 400 mL of shaken vigorously and a suitable aliquot of well- sample until a negative test with starch-iodide mixed sample withdrawn. paper is obtained. 3.2.4 Most remaining interferences are re­ 2. Summary of method moved by the distillation. This method is based on the chlorination of 3.3 This method includes no provisions for cyanide and the subsequent reaction of the removing these interferences or for minimizing product with a mixed solution of pyridine- their effects in water-suspended sediment and pyrazolone to form a stable complex dye. The bottom material. The analyst must be aware method detects only simple cyanides; therefore, that, when such interfering substances are pres­ any complex cyanides present must be broken ent, the analytical result obtained may be in down. The decomposition of complex cyanides error, although distillation of the cyanide cer­ is accomplished by an acid reflux and distilla­ tainly separates it from some of the interfering tion prior to the colorimetric procedure. The substances. distillation also removes certain interferences from water samples. 4. Apparatus 4.1 Distillation train (fig. 23). An efficient 3. Interferences gas washer is essential to the proper operation 3.1 Common interferences include sulfide, of the distillation assembly. The Fisher-Milligan heavy-metal ions, fatty acids, steam-distillable unit has been found satisfactory. organic compounds, cyanate, thiocyanate, gly- 4.2 Heating element for Claisen flask. cine, urea, oxidizing agents, and substances that 4.3 Spectrometer for use at 620 nm. may contribute color or turbidity to the sample. 4.4 Refer to the manufacturer's manual to 3.2 These interferences may be removed or optimize instrument. their effect minimized as follows: 3.2.1 Sulfide can be removed as lead sulfide 5. Reagents by adding a slight excess of lead carbonate to 5.1 Acetic acid, 3M: Mix 172 mL glacial 400 mL of the alkaline (pH 11.0 or above) sam­ HC2H3O2 (sp gr 1.06) with demineralized water ple. Filter the sample immediately, wash the and dilute to 1 L. 209 210 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Allihn water-cooled condenser. 9-mm OD

Thistle tube

Standard tapered joint—

Screw clamp

500-mL suction flask 500-mLmodified Fisher-Milligan Claisen flask spiral gas washer

Figure 23.—Cyanide, distillation train

5.2 Chloramine-T solution, 1 g/100 mL: Dis­ 5.4 Cyanide standard solution II, 1.00 solve 0.25 g chloramineT in 25 mL deminer- mL = 0.010 mg CN: Add 10.0 mL cyanide stand­ alized water. This solution is unstable and must ard solution I to demineralized water and dilute be prepared immediately before use. When a to 1,000 mL. This solution must be prepared blank and standards are used, the chloramine-T fresh before usa solution may be used throughout a period of 5.5 Cyanide standard solution III, 1.00 several hours, but each succeeding use results mL = 0.001 mg CN: Add 10.0 mL cyanide stand­ in lower absorbance readings for the same con­ ard solution II to demineralized water and dilute centration of cyanide. to 100 mL. This solution must be prepared fresh 5.3 Cyanide standard solution I, 1.00 mL = before usa 1.00 mg CN: Dissolve 2.50 g KCN (NOTE 1) in 5.6 Magnesium chloride solution, 24 g/100 1 L demineralized water. Standardize with silver mL: Dissolve 51 g MgCl2-6H2O in 100 mL nitrate standard solution, 1.00 mL = 1.00 mg demineralized water. CN, as follows: Adjust the pH of 5.0 mL cyanide 5.7 5-(p-Dimethylaminobenzylidene)rhoda- standard solution I to 11.0 or above, and dilute mine indicator solution, 0.02 g/100 mL: Dissolve to 250 mL with demineralized water. Add 0.5-1.0 0.02 g 5-(p-dimethylaminobenzylidene)rhodamine mL 5-(p-dimethylaminobenzylidene)rhodamine in 100 mL acetone. Eastman Kodak No. 2748 has indicator solution and titrate with standard silver been found satisfactory. nitrate solution to the first color change from 5.8 Pyrazolone solution I: Add 0.8 g canary yellow to salmon. Subtract the blank ob­ l-phenyl-3-methyl-5-pyrazolone to 150 mL tained by titrating an identical volume of water, demineralized water at 75 °C. Cool to room alkali, and indicator. The cyanide solution is temperature, with stirring; filter. Eastman Kodak unstable and must be either restandardized No. 1397 has been found satisfactory. weekly or prepared fresh when needed. 5.9 Pyrazolone solution II: Dissolve 0.025 g NOTE 1. CAUTION—POISON: May be fatal bis-pyrazolone in 25 mL pyridine and filter. if swallowed or inhaled. Contact with acid Eastman Kodak No. 6969 has been found liberates poisonous gas. Contact with KCN may satisfactory. Several minutes of mixing are usual­ burn eyes and irritate skin. ly required to effect solution. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 211 5.10 Pyridine-pyrazolone reagent: Mix 125 the condenser to the gas washer, and the gas mL pyrazolone solution I with 25 mL washer with small amounts of demineralized pyrazolone solution II. After standing, the water and add to contents of flask. Dilute con­ mixed reagent develops a pink color which does tents of volumetric flask to 200 mL. not affect color development. Prepare this 6.6 Refill the gas washer with NaOH and reagent fresh daily or before each use. demineralized water, as in 6.2, and repeat reflux 5.11 Pyridine. procedure. If only readily hydrolyzed cyanides 5.12 Silver nitrate standard solution, 1.00 mL are present, the absorber liquid from the first 1.00 mg CN: Crush approx 5 g of AgNO3 reflux period will contain all the available crystals and dry to constant mass at 40 °C. cyanide. If stable complex cyanides are present, Dissolve 3.2647 g AgNO3 in demineralized a measurable yield will appear in the absorber water and dilute to 1 L. This solution is needed liquid during the second and succeeding reflux only to standardize the cyanide standard solu­ periods, depending on the degree of stability of tion I. the compounds. 5.13 Sodium hydroxide, 1M: Dissolve 4 g 6.7 Colorimetric procedure: The standards NaOH in 100 mL demineralized water. and many of the reagents used in this procedure 5.14 Sulfuric acid, concentrated (sp gr 1.84). are unstable and must be prepared immediate­ ly before use if maximum color development is 6. Procedure to be obtained. The color development is also 6.1 Distillation: Follow instructions in dependent on the presence of approximately paragraph 6.1.1 for water or water-suspended equal total-salt concentrations in both samples sediment and paragraph 6.1.2 for bottom and standards. If the final distillate volume is material, after assembling the distillation train, 200 mL, it will be about 0.25M in NaOH. For consisting of Claisen flask, thistle tube, con­ this reason 0.25M NaOH must be used for dilu­ denser, gas washer, screw clamp, suction flask, tions and for the standards and blank. Any and aspirator. substantial deviation in the quantity of 3M 6.1.1 Add 400 mL water or water-suspended HC2H3O2 required to neutralize blank and sediment (or smaller aliquot diluted to 400 mL) standards will require additional manipulation to the boiling flask. to bring these volumes into approximate agree­ 6.1.2 Add a weighed portion (5-10 g) of ment. The variation should be less than 0.3 mL. bottom-material and 250-500 mL demineralized 6.8 Prepare a blank by pipetting 15 mL of water to the boiling flask. 0.25M NaOH into a 23-mm absorption cell fit­ 6.2 Add exactly 50 mL 1M NaOH and 100 ted with a rubber stopper. Prepare standards mL demineralized water to the gas washer. Con­ containing 0.0005 mg and 0.001 mg CN, each nect train and adjust suction so that 1 or 2 bub­ diluted to 15 mL with 0.25M NaOH in similar bles per second enter the boiling flask through containers. the air inlet. Do not increase airflow beyond 2 6.9 Take 15-mL aliquots (or smaller volumes bubbles per second. diluted to 15 mL with 0.25M NaOH) of the 6.3 Add 10 mL MgCl2 solution through the distillates from the purification procedure and thistle tube, and allow the airflow to mi* for 3 place in 23-mm stoppered absorption cells. min. Rinse air tube with demineralized water, 6.10 Neutralize each sample, blank, and then slowly add 20 mL concentrated H2SO4. standard with 3M HC2H3O2 using phenol- Rinse the tube again. phthalein indicator solution. 6.4 Heat at a rate that produces rapid boil­ 6.11 To each sample, blank, and standard add ing, but not enough to flood the condenser in­ 4 drops chloramine-T solution, stopper, and let or permit the vapors to rise more than shake. Allow 2 min for the reaction to proceed. halfway into the condenser. Reflux for 1 h. Turn 6.12 Add 5.0 mL pyridine-pyrazolone reagent off heat, but permit airflow to continue for 15 and miy well. Allow 20 min for color devel­ min. opment. 6.5 Transfer gas washer contents to a 6.13 Read absorbances at 620 nm. The color 200-mL volumetric flask. Wash the tube, from is stable for 30 min. The absorbance decreases 212 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS slowly over a period of 3 h and can probably be 1000 mL distillate CN(mg/L) = read during this period with some decrease in wt of sample (g) mL aliquot accuracy. 1 sample X X mg standard 7. Calculations 7.1 Determine the concentration of dis­ where solved or total cyanide in milligrams per liter as follows: ^sample ~ absorbance of sample, and A = absorbance of standard. 1000 mL distillate CN(mg/L) mL original mL aliquot 8. Report sample 8.1 Report cyanide, dissolved (00723) and total (00720), concentrations as follows: less ^sample X ———— x mg standard than 1.0 mg/L, nearest 0.01 mg/L; 1.0 mg/L and above, two significant figures. 8.2 Report cyanide, total-in-bottom-material where (00721), concentrations as follows: less than 10 ^sample = absorbance of sample, mg/kg, nearest 0 .1 mg/kg; 10 mg/kg and above, and two significant figures. ^std, = absorbance of standard. 7.2 Determine the concentration of cyanide 9. Precision in bottom-material samples in milligrams per Precision data are not available for this kilogram as follows: method. Density, gravimetric

Parameter and Code: Density 1-1312-85 (g/mL at 20°C): 71820

1. Application 6.2 Using a previously calibrated 50-mL This method may be used to determine the pipet, transfer the sample to a tared weighing density of any water from which the suspended bottle. sediment has been satisfactorily removed. 6.3 Stopper the bottle immediately to pre­ vent water loss by evaporation. 2. Summary of method 6.4 Weigh the solution to the nearest 0.1 mg. The density determination is based on the weight of a carefully measured volume of filtered 7. Calculations sample at a given temperature. Densities are de­ 7.1 Determine density as follows: termined at 20 °C, the same temperature at which volumetric glassware is calibrated. Density = g sample 3. Interferences mL sample The only significant interference with this method is suspended sediment, which may usu­ ally be removed by filtration, centrifugation, or 7.2 If a constant-temperature bath is not flocculation. Precautions should be taken to min­ available, the determination can be made at the imize evaporation during removal of sediment. sample temperature and a correction applied for the departure from 20 °C. The temperature is 4. Apparatus recorded with an accurate thermometer, and the 4.1 Pipet, volumetric, 50 mL calibrated: The relative density for that temperature obtained actual volume delivery of the pipet is deter­ from a table. The density result is then cor­ mined by weighing a delivering volume of rected by the factor: demineralized water at 20 °C. The volume is ob­ tained from relative-density tables in hand­ books. Alternatively, 50-mL pycnometer can be _____Relative density (20 °C)_____ used; it must also be calibrated. Relative density (test temperature in°C) 4.2 Water bath, constant temperature, 20 + 0.5°C. 4.3 Weighing bottle, 50-mL capacity. 8. Report Report density (71820) to three decimal places 5. Reagents in terms of grams per millimeter at 20 °C. None required. 9. Precision 6. Procedure Precision data are not available for this 6.1 Adjust the temperature of the filtered method, but results are believed reproducible to sample to 20.0 °C. + 0.005 g/mL. 213

Fluoride, colorimetric, zirconium-eriochrome cyanine R

Parameters and Codes: Fluoride, dissolved, 1-1325-85 (mg/L as F): 00950 Fluoride, total, I-3325-85 (mg/L as F): 00951 Fluoride, suspended total I-7325-85 (mg/L as F): 82299

1. Application attack minerals such as fluorspar in water- 1.1 This method may be used to analyze suspended sediment. Samples that contain a water, brines, and water-suspended sediment high concentration of dissolved solids need to containing from 0.1 to 3.0 mg/L of fluoride. be distilled. The method also eliminates in­ Higher concentrations need to be reduced by terferences noted below. A fixed volume of sam­ dilution. If the fluoride concentration exceeds ple is added to a sulfuric acid solution having 30 mg/L, determine fluoride by the ion- selective a specific boiling point and is distilled until an electrode method (1-1327). identical volume is recovered (Bellack, 1958). 1.2 Suspended total fluoride is calculated by The fluoride is distilled as fluosilicic acid. subtracting dissolved fluoride from toted fluoride. 3. Interferences 1.3 The total fluoride in water-suspended 3.1 Under the experimental conditions, the sediment is determined after each sample is dye does not give a color with titanium or beryl­ shaken vigorously and a suitable aliquot of well- lium, two metals that react with many other zir­ mixed sample is rapidly withdrawn and then conium agents. Aluminum decreases the distilled. apparent fluoride concentration. This interfer­ ence is eliminated by allowing the solution to 2. Summary of method stand for at least 2 h before measuring the ab­ 2.1 The zirconium-eriochrome cyanine R sorbance. As much as 10,000 jig/L of aluminum method given here is a modified version of the can be tolerated. procedure of Megregian (1954). 3.2 Analytical conditions are not overly 2.2 In acid solution, zirconium reacts with critical. The pH is controlled at a highly acid eriochrome cyanine R to form a read complex level by the addition of 1.7 mL of concentrated ion. Fluoride forms a more stable complex with hydrochloric acid to each sample. This assures zirconium (ZrFg2) and withdraws zirconium that high concentrations of bicarbonate or other from the organic complex to produce a bleach­ alkaline ions will not affect the pH significantly. ing effect. Eriochrome cyanine R shows a de­ Sulfate interferes but is removed by precipita­ cided specificity to zirconium. tion as barium sulfate. Overnight standing is 2.3 The quality of the eriochrome cyanine R usually required to ensure complex settling of from different sources differs significantly, and barium sulfate before measuring the absorb­ it is necessary to test the reagent each time that ance. The clarification of the sample can be ac­ it is prepared. The individual absorbance curves celerated by centrifuging if immediate results show corresponding differences, and the sensi­ are required. Filtration should not be used tivity of fluoride between reagents may differ because of loss of color by adsorption on the by 20 percent. filter medium. 2.4 The method includes a distillation step 3.3 Residual chlorine, chromate, and prob­ to decompose organic fluoride compounds and ably other strong oxidants attack the dye. 215 216 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Stannous chloride is used to eliminate chromate 12-mm ID and chlorine interference* Chromium, cadmium, Connecting tube and nickel, in concentrations of less than 5,000 /ig/L, do not interfere. When the fluoride con­ centration exceeds 1.0 mg/L, larger quantities of these metals can be tolerated. Ten mg/L of cyanide or phosphate and 10,000 /ig/L of iron, or zinc, or lead cause no appreciable interference Thermometer if the sample is allowed to stand overnight. 3.4 * The determination shows "salt effect"; Rubber sleeve Condenser the sensitivity is depressed by 5-10 percent at a dissolved-solids concentration of 10,000 mg/L. The effect of the usual type of color is not serious. A color of 70 on the platinum-cobalt scale is equivalent to an absorbance error of only 0.005 in the spectrophotometric measure­ ment. Thus, it appears that color correction will not often be necessary. Highly colored or highly mineralized samples need to be distilled. 3.5 The method has rather good tolerance for temperature differences. For most purposes, 250-mL operating at room temperature without other Volumetric flask precautions is satisfactory.

4. Apparatus 4.1 Distillation assembly (fig. 24), consisting Figure 24.—Fluoride, distillation assembly of a round-bottom distilling flask, adapter, con­ necting tube, condenser, receiving flask, and thermometer, 250 °C. 5.5 Mixed indicator solution: To about 300 4.2 Spectrometer, for use at 540 nm, and mL demineralized water, add 20.0 mL erio­ cells with a mimimum light-path length of 4 cm* chrome cyanine R solution and 10.0 mL ZrO(NO3)2-2H2O solution. Add 70 mL concen­ 5. Reagents trated HC1 (sp gr 1.19) and 4 g BaCl2. Dissolve 5.1 Eriochrome cyanine R solution, 0.90 and dilute to 1,000 mL with demineralized g/100 mL; Dissolve 1.80 g tested eriochrome water. cyanine R in water and dilute to 200 mL. The NOTE 1. It is practical to prepare more than National Aniline Co. product labeled "alizarol 1 L of mixed indicator solution at a time. Eigh­ cyanine RC" has been used successfully. A teen liters, contained in a 5-gallon reagent bot­ precipitate sometimes forms when the solution tle, seems to be a practical volume. If this is prepared, but the solution may be filtered volume is prepared, the component solutions prior to use. must be prepared in correspondingly larger 5.2 Fluoride standard solution I, 1.00 mL = volumes. 0.10 mg P-1: Dissolve 0.2210 g NaF in NOTE 2. Once prepared, the mixed indicator demineralized water and dilute to 1,000 mL. solution should be allowed to stand for about 5.3 Fluoride standard solution II, 1.00 1 week in order to permit any precipitate to set­ mL = 0.01 mg F'1: Dilute 100 mL fluoride tle to the bottom of the bottle. The reagent is standard solution I to 1,000 mL with then used without disturbing the precipitate. demineralized water. 5.6 Silver sulfate, powder. 5.4 Hydrochloric acid, 6M: Mix 50 mL 5.7 Stannous chloride solution, 1.7 g/100 concentrated HC1 (sp gr 1.19) with demineral­ mL: Dissolve 1.0 g SnCl2-2H2O in 10 mL ized water and dilute to 100 mL. concentrated HC1 (sp gr 1.19) and dilute to 50 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 217 mL with demineralized water. This solution is 6.2.5 Allow the solution to stand overnight for unstable. Prepare fresh daily. barium sulfate to settle. 5.8 Sulfuric acid, concentrated (sp gr 1.84). 6.2.6 Decant approximately 25 mL clear 5.9 Zirconyl nitrate solution, 0.21 g/100 mL: supernatant solution, taking care not to disturb Dissolve 0.49 g ZrO(NO3)2 2H2O in 200 mL 6M the precipitate. HC1. 6.2.7 Determine the absorbance of each sam­ ple and standard against the blank, which is set 6. Procedure at an absorbance of 1.50 (NOTE 3); when nec­ 6.1 Distillation: essary, make correction for water color. 6.1.1 Place 400 mL demineralized water in a NOTE 3. Alternatively, measurement of 1-L distilling flask containing a few glass beads. transmittance may allow some instruments to Cautiously, and with constant swirling, add 200 be calibrated so that concentration can be read mL concentrated H2SO4. Connect the flask to directly. the condenser assembly and distill until the temperature of the acid mixture reaches 180 °C. 7. Calculations At this point the proper acid concentration has 7.1 Determine milligrams of fluoride in each been reached. The acid need not be replaced un­ sample solution from a plot of absorbances of til the accumulation of nonvolatile material is standards. sufficient to cause interference. An occasional 7.2 Determine the dissolved or total-fluoride recovery check with a standard fluoride sample concentration in milligrams per liter as follows: will indicate the need for replacement. 1,000 6.1.2 Cool to room temperature. F (mg/L) = ——————— X mg F in sample 6.1.3 Cautiously, and with constant swirl­ mL sample ing, add 250 mL well-mixed sample to the acid mixture in the distillation flask. 7.3 To determine milligrams per liter of 6.1.4 Distill until 250 mL of distillate has been suspended total fluoride, subtract dissolved- collected, and the temperature of the acid mix­ fluoride concentration from total-fluoride con­ ture has returned to 180 °C. When the tempera­ centration. ture of the acid mixture at the completion of the distillation exceeds 183 °C, add 50 mL deminer­ 8. Report alized water and distill the mixture until the Report fluoride, dissolved (00950), total temperature again reaches 180 °C. After distill­ (00951), and suspended-total (82299), concentra­ ing a high-fluoride sample (3 mg/L or more), tions as follows: less than 10 mg/L, one decimal; clean the apparatus by distilling 250 mL of 10 mg/L and above, two significant figures. water. This prevents a carryover of fluoride in subsequent samples. When samples with high- 9. Precision chloride content are to be distilled, Ag2SO4 9.1 Precision for dissolved fluoride for 30 should be added to the distilling flask in pro­ samples within the range of 0.3 to 3.7 mg/L may portion of 5 mg per milligram of Cl"1. be expressed as follows: 6.2 Cohrimetric procedure: 6.2.1 Pipet a volume of filtered sample or a 0.006 volume of the cooled distillate (step 6.1.4) con­ taining less than 0.03 mg F'1 (10.0 mL max) in­ where to a 50-xnL centrifuge tube or test tube. ST = overall precision, milligrams per liter, 6.2.2 Prepare a blank and sufficient stand­ and ards, and adjust the volume of each to 10.0 mL. X=concentration of fluoride, milligrams per 6.2.3 If chromate, residual chlorine, or other liter. strong oxidizing agents are present in the sam­ The correlation coefficient is 0.8048. ple, add 0.1 mL SnCl2 solution and let the solu­ 9.2 Precision for dissolved fluoride for four tion stand for 10 minutes. of the 30 samples expressed in terms of the per­ 6.2.4 Add 25.0 mL mixed indicator solution. cent relative standard deviation is as follows: 218 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Number of Mean Relative standard deviation laboratories (mo/U _____(percent)_____ total fluoride will be greater than that reported for dissolved fluoride. 34 0.30 17 17 1.06 7 3 2.00 15 References 9 3.69 13 Bellack, Ervin, 1958, Simplified fluoride distillation method: American Water Works Association Journal, v. 50, p. 530-5. Megregian, Stephen, 1954, Rapid spectrophotometric deter­ 9.3 It is estimated that the percent relative mination of fluoride with zirconium-eriochrome cyanine standard deviation for total and suspended R lake: Analytical Chemistry, v. 26, p. 1161-66. Fluoride, electrometric, ion-selective electrode

Parameter and Code: Fluoride, dissolved, 1-1327-85 (mg/L as F): 00950

1. Application addition of the buffer solution will adjust the This method is applicable to the measurement pH of most samples to between 5.0 and 5.5. of dissolved fluoride in finished water, natural 3.3 Several polyvalent cations capable of water, brines, and industrial wastewater. Con­ complexing fluoride ion interfere. These include centrations of at least 0.1 mg/L can be deter­ iron(III), aluminum(III), and silicon dioxide. mined. Samples containing more than 3 mg/L The extent of their interference is proportional of fluoride need to be diluted. to their concentration, so that dilution of the sample with an equal volume of buffer solution 2. Summary of method reduces the interference. The (1,2-cyclohexylene- 2.1 Fluoride is determined potentiometrical- dinitrilo)tetraacetic acid (CDTA) in the buffer ly in a buffered sample with use of an ion-se­ solution complexes as much as to 10,000 fig lective (fluoride) electrode in conjunction with iron(III), 2,000 jtg aluminum(III), and 100 mg a standard calomel reference electrode (SCE), silicon dioxide. and a pH meter having an expanded millivolt 3.4 Orthophosphate-phosphorus concentra­ scale (Frant and Ross, 1968). tions of 25 mg/L and sulfate and chloride con­ 2.2 The fluoride electrode consists of a laser- centrations of 3,000 mg/L do not interfere type doped lanthanum fluoride crystal, across (Harwood, 1969). which a potential is developed by fluoride ions. The cell may be represented by: 4. Apparatus 4.1 Fluoride ion-selective electrode. Ag/AgCl, Cl'1 (0.3M), 4.2 pH meter, with expanded scale. 4.3 Reference electrode, standard calomel, F'1 (0.001Af)/LaF3/test solution/SCE. sleeve-type. 4.4 Stirrer, magnetic, Teflon-coated stirring bar. 3. Interferences 3.1 The ion-selective electrode measures 5. Reagents fluoride-ion activity, so that high concentrations 5.1 Buffer solution, pH 5.0 to 5.5: To approx of dissolved solutes (which lower the ion-activity 500 mL demineralized water in a 1-L beaker, add coefficient) cause an error in the determination. 57 mL glacial HC2H3O2, 58 g NaCl, and 4.5 g Addition of the buffer solution, which contains (1,2-cyclohexylenedinitrilo) tetraacetic acid a high concentration of dissolved solutes, effect­ (CDTA). Stir to dissolve and cool to room tem­ ively masks minor variations in the salt content perature. Adjust the pH of the solution to be­ of the samples and, therefore, minimizes this tween 5.0 and 5.5 with 5M NaOH (about 170 error. mL will be required). Dilute to 1 L with demin- 3.2 The optimum pH for measurement is be­ eralized water. tween 5.0 and 8.5. Below this range, hydro­ 5.2 Fluoride standard solution /, 1.00 mL = fluoric acid is only slightly dissociated, and 0.10 mg F'1: Dissolve 0.2210 g NaF in above a pH of 8.5, hydroxyl ion interferes. The demineralized water and dilute to 1,000 mL. 219 220 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Fluoride standard solution II, 1.00 trations as follows: less than 10 mg/L, one mL = 0.01 mg F'1: Dilute 100 mL fluoride decimal; 10 mg/L and above, two significant standard solution I to 1,000 mL with figures. demineralized water. 9. Precision 6. Procedure 9.1 The standard deviation for dissolved 6.1 Adjust pH meter according to manufac­ fluoride within the range of 0.03 to 2.14 mg/L turer's instructions. for 27 samples was found to be independent of 6.2 Pipet 25.0 mL sample into 100-mL concentration. The 95-percent confidence inter­ beaker. val for the average standard deviation of 0.14 6.3 Prepare a series of four standards con­ mg/L ranged from 0.135 to 0.153 mg/L. taining 0.1,1.0, 2.0, and 3.0 mg/L F"1, and pipet 9.2 Precision for dissolved fluoride for five 25.0 mL of each into 100-mL beakers. of the 27 samples expressed in terms of the per­ 6.4 Add 25.0 mL buffer solution to each cent relative standard deviation is as follows: sample and standard. 6.5 Place beaker on magnetic stirrer, im­ Number of Mean Relative standard deviation merse electrodes, and measure potential while laboratories «pg/L) _____(percent)_____ mixing. The electrodes must remain in the solu­ 16 0.03 167 tion until reading has stabilized. This may re­ .32 41 quire 5 min or more. 13 .55 35 16 1.01 15 17 2.14 11 7. Calculations 7.1 Construct a graph of potential in milli­ volts (mV) versus concentration of standards References (mg/L) on semilog paper, with the concentra­ tions plotted on the logarithmic axis. Frant, M. S., and RGBS, J. W., Jr., 1968, Use of a total ionic 7.2 From the graph, determine the milli­ strength adjustment buffer for electrode determination grams per liter of fluoride in each sample. of fluoride in water samples: Analytical Chemistry, v. 40, p. 1169-71. Harwood, J. E., 1969, The use of an ion-selective electrode 8. Report for routine fluoride analysis on water samples: Water Report fluoride, dissolved (00950), concen­ Research, v. 3, p. 273-80. Fluoride, electrometric, ion-selective electrode, automated- segmented flow

Parameters and Codes: Fluoride, dissolved, 1-2327-85 (mg/L as F): 00950 Fluoride, total, 1-4327-85 (mg/L as F): 00951 Fluoride, suspended total, I-7327-85 (mg/L as F): 82299

1. Application is added to a sulfuric acid solution having a spe­ 1.1 This method may be used to analyze water cific boiling point and is distilled until an iden­ and water-suspended sediment containing from tical volume is recovered (Bellack, 1958). The 0.1 to 3.0 mg/L of fluoride with conductivities fluoride is distilled as fluosilicic acid. less than 20,000 /iS/cm. Samples with higher conductivities need to be distilled. 3. Interferences 1.2 Suspended total fluoride is calculated by 3.1 The ion-selective electrode measures subtracting dissolved fluoride from total fluoride, fluoride-ion activity; thus, high concentrations 1.3 Total fluoride in water-suspended sedi­ of dissolved solutes (which lower the ion-activity ment is determined after each sample is shaken coefficient) cause an error in the determination. vigorously and a suitable aliquot of well-mixed Addition of a buffer solution that contains a sample is rapidly withdrawn and then distilled. high concentration of dissolved solutes effect­ ively masks minor variations in the salt content 2. Summary of method of the samples and, therefore, minimizes this 2.1 Fluoride is determined potentiometrical- error. ly in a buffered sample with use of an ion-selec­ 3.2 The optimum pH for measurement is be­ tive (fluoride) electrode in conjunction with a tween 5.0 and 8.5. Below this range, hydro­ standard calomel reference electrode (SCE) and fluoric acid is only slightly dissociated, and with a pH meter having an expanded millivolt above a pH of 8.5, hydroxyl ion interferes. The scale (Frant and Ross, 1968; Harwood, 1969; addition of the buffer solution will adjust the Bellack, 1958). pH of most samples to between 5.0 and 5.5. 2.2 The fluoride electrode consists of a laser- 3.3 Several polyvalent cations capable of type, doped lanthanum fluoride crystal, across complexing fluoride ion interfere. These include which a potential is developed by fluoride ions. iron(III)v aluminum(III), and silicon dioxide. The cell may be represented by: The extent of their interference is proportional to their concentration, so that dilution of the Ag/AgCl, CH (0.3M), sample with an equal volume of buffer solution reduces the interference. The (1,2-cyclohexylene- F-1 (O.OOLM)/LaF3/test solution/SCE. dinitrilo)tetraacetic acid (CDTA) in the buffer solution complexes up to 10,000 fig iron(III), This electrode deteriorates in time and must be 2,000 /ig aluminum(III), and 100 mg silicon replaced when results become erratic. dioxide. 2.3 The method includes a distillation step 3.4 Orthophosphate-phosphorus concentra­ to decompose organic fluoride compounds and tions of 25 mg/L and sulfate and chloride con­ attack minerals such as fluorspar in water- centrations of 3,000 mg/L do not interfere suspended sediment. A fixed volume of sample (Harwood, 1969). 221 222 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

4. Apparatus 12-mm ID 4.1 Distillation assembly, (fig. 25), consist­ Connecting tube ing of a round-bottom distilling flask, adapter, connecting tube, condenser, receiving flask, and thermometer (250 °C). 4.2 Technicon AutoAnalyzer II, consisting of a sampler, proportioning pump, cartridge Thermometer manifold, heating bath, recorder, potentiometer,

and printer. Rubber sleeve Condenser 4.3 Fluoride ion-selective electrode. 4.4 Reference electrode, standard calomel. 4.5 With this equipment a 40/h (2/1) cam has Adapter been found satisfactory for the range from 0.1 to 3.0 mg/L; 5. Reagents 5.1 Brij-35 solution: 30-percent aqueous solu­ tion (Baker Cat. No. C 706 or equivalent). 1000-mL 5.2 Buffer solution, 0.33 mg/L, pH 5.0 to 5.5: Boiling flask To approx 500 mL demineralized water in a 1-L beaker, add 57 mL glacial HC2H3O2, 58 g NaCl, 250-mL and 4.5 g (1,2-cyclohexylenedinitrilo) tetraacetic Volumetric flask acid (CDTA). Stir to dissolve and cool to room temperature. Adjust the pH of the solution be­ tween 5.0 and 5.5 with 5M NaOH (about 170 mL will be required). Filter if necessary and add Figure 25.—Fluoride, distillation assembly 33 mL of fluoride standard solution II and 0.5 mL of Brij-35 solution. Dilute to 1,000 mL with 6. Procedure demineralized water. 6.1 Distillation procedure: Water-suspended 5.3 Fluoride standard solution I, 1.00 mL = sediment needs to be distilled. The distillation 1.00 mg F: Dissolve 2.2101 g NaF in demineral­ may be omitted for samples for determining dis­ ized water and dilute to 1,000 mL. solved fluoride if the specific conductance is less 5.4 Fluoride standard solution II, 1.00 mL = than 20,000 /*S/cm. 0.01 mg F: Dilute 10.0 mL fluoride standard solu­ 6.1.1 Place 400 mL demineralized water in a tion I to 1,000 mL with demineralized water. 1-L distilling flask containing a few glass beads. 5.5 Fluoride working standards: Prepare a Cautiously, and with constant swirling, add 200 blank and 500 mL each of a series of fluoride mL concentrated H2SO4. Connect the flask to working standards by appropriate quantitative the condenser assembly and distill until the dilution of fluoride standard solution II as temperature of the acid mixture reaches ISO °C. follows: At this point the proper acid concentration has Fluoride standard solution Fluortde concentration been reached. The acid need not be replaced un­ (ml) (mg/L) til the accumulation of nonvolatile material is oo oo sufficient to cause interference. An occasional 10.0 .20 recovery check with a standard fluoride sample 25.0 .50 50.0 1.00 will indicate the need for replacement. 75.0 1.50 6.1.2 Cool to room temperature. 100.0 2.00 6.1.3 Cautiously, and with constant swirl­ 125.0 2.50 150.0 3.00 ing, add 250 mT. of well-mixed sample to the acid mixture in the distillation flask. 5.6 Silver sulfate, powder. 6.1.4 Distill until 250 mL distillate has been 5.7 Sulfuric acid, concentrated (sp gr 1.84). collected and the temperature of the acid METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 223 mixture has returned to 180 °C. When the (the first two positions should both contain temperature of the acid mixture at the comple­ 3-mg/L standards). Place individual standards tion of the distillation exceeds 183°C, add 50 of differing concentrations in every eighth posi­ mL distilled water and distill the mixture until tion of the remainder of this and subsequent the temperature again reaches 180°C. After sample trays. Fill remainder of each sample tray distilling a high fluoride sample (3 mg/L or with unknown samples. more), clean the apparatus by distilling 250 mL 6.2.6 Begin analysis. When the peak from the water. This prevents a carryover of fluoride in second 3-mg/L standard appears on the re­ subsequent samples. When samples with high corder, adjust the STD CAL control until the chloride content are to be distilled, AgSO4 flat portion of the peak reads 100 scale should be added to the distilling flask in pro­ divisions. portion of 5 mg per milligram of Cl"1. 6.2 Electrometric procedure: 7. Calculations 6.2.1 Set up manifold (fig. 26). 7.1 Prepare an analytical curve by plotting 6.2.2 Allow potentiometer, recorder, and the height of each standard peak versus its heating bath to warm up for at least 30 min or respective fluoride concentration. This curve until the temperature of the heating bath should be linear or very nearly linear. reaches 37 °C. 7.2 Compute the concentration of dissolved 6.2.3 Calibrate the potentiometer according or total fluoride in each sample by comparing to the manufacturer's instructions. its peak height to the analytical curve. Any 6.2.4 Adjust the baseline to read 10 scale divi­ baseline drift that may occur must be taken into sions on the recorder with all reagents, but with account when computing the height of a sam­ demineralized water in the sample line. ple or standard peak. 6.2.5 Place a complete set of standards in the 7.3 Tb determine milligrams per liter of sus­ first positions of the first sample tray, beginning pended total fluoride, subtract dissolved-fluoride with the most concentrated working standard concentration from total-fluoride concentration.

Waste To sampler 4 0.073 in Water wash receptacle 2.00 ml/nun

Heating bal h 0.030 in Air arc 0.32 mL/miii 11Hum coil 0.051 in Sample ^\ iler v»— nmn nmn ^ * 1.00 mL/nin (L) des 0.051 in B'ffer Samoler 4

Figure 26.—Fluoride, ion-selective electrode manifold 224 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 8. Report 9.3 It is estimated that the percent relative Report fluoride, dissolved (00950), total standard deviation for total and suspended (00951), and suspended-total (82299), concentra­ total fluoride will be greater than that reported tions as follows: less than 10 mg/L, one decimal; for dissolved fluoride. 10 mg/L and above, two significant figures.

9. Precision References 9.1 The standard deviation for dissolved fluoride within the range of 0.33 to 1.28 mg/L Bellack, Ervin, 1958, Simplified fluoride distillation method: for nine samples was found to be independent American Water Works Association Journal, v. 50, of concentration. The 95-percent confidence in­ p. 530-5. terval for the average standard deviation of 0.07 Erdmann, D.E., 1975, Automated ion-selective method for mg/L ranged from 0.05 to 0.09 mg/L. determining fluoride in natural waters: Environmental 9.2 Precision for dissolved fluoride for three Science and Technology, v. 9, p. 252-3. of the nine samples expressed in terms of the Frant, M. S., and Ross, J. W., Jr., 1968, Use of a total ionic percent relative standard deviation is as follows: strength adjustment buffer for electrode determination of fluoride in water supplies: Analytical Chemistry, Number of Mean Relative standard deviation laboratories (mg/L) _____(percent)_____ v.40, p. 1169-71. 3 0.33 18 Harwood, J. E., 1969, The use of an ion-selective electrode 8 1.09 6 for routine fluoride analysis on water samples: Water 4 1.28 7 Research, v. 3, p. 273-80. Fluoride, ion-exchange chromatographic, automated

Parameters and Codes: Fluoride, dissolved, 1-2057-85 (mg/L as F): 00950 Fluoride, dissolved, 1-2058-85 (mg/L as F): 00950

2. Summary of method anions in their acid form are measured using an Fluoride is determined sequentially with six electrical-conductivity cell. See method 1-2057, other anions by ion-exchange chromatography. anions, ion-exchange chromatographic, auto­ Ions are separated based on their affinity for mated, and method 1-2058 anions, ion-exchange the exchange sites of the resin. The separated chromatographic, precipitation, automated. 225

Hardness, calculation

Parameter and Code: Hardness, 1-1340-85 (mg/L as CaCO^: 00900

1. Application 7. Calculations This method may be used to calculate hard­ Hardness as mg/L CaCO3 = ness for any sample for which determined values for barium, calcium, strontium, and Sme/L(Ca + Mg + Ba + Sr> X 50.05. magnesium are available. 8. Report 2. Summary of method Report hardness, calculated, as CaCO3 Hardness is computed from the individual (00900), concentrations as follows: less than 10 determinations of the alkaline earths. This is mg/L, whole numbers, 10 mg/L and above, two best accomplished by summing the milli- significant figures. equivalents per liter of calcium, magnesium, strontium, and barium. In many cases the con­ 9. Precision tributions of strontium and barium are insig­ Precision data are not available for this nificant compared to those of calcium and method, but reproducibility should be com­ magnesium and can safely be ignored. parable to those of the individual determinations. 227

Hardness, titrimetric, complexometric

Parameter and Code: Hardness 1-1338-85 (mg/L as CaCO^: 00900

1. Application indicator to form discolored oxidation products. This procedure is applicable to most natural Hydroxylamine hydrochloride reagent is used and treated water, but the method fails con­ to reduce manganese to the divalent state. The spicuously at times with acidic or polluted water divalent manganese interference can be re­ that contains excessive amounts of heavy moved by addition of one or two small crystals metals. of potassium ferrocyanide. 3.3 In the presence of high aluminum con­ 2. Summary of method centrations, a characteristic effect will be 2.1 Disodium dihydrogen ethylenediamine- observed as the end point is approached. The tetraacetate (Na2EDTA) forms a slightly ion­ blue color that indicates the end point will ap­ ized, colorless, stable complex with alkaline- pear and then, after short standing, will revert earth ions. The indicator Eriochrome Black T to red. The reversion should not be confused is bright blue in the absence of alkaline earths, with the gradual change that normally takes but with them forms a deep-red complex that place in the titrated sample several minutes has a higher ionization constant than that of the after the titration has been completed. Na2EDTA complex. Hence, with Eriochrome Black T as an indicator, the alkaline earth can 4. Apparatus be titrated with Na2EDTA. Visual-titration assembly: Some analysts 2.2 All alkaline earths titrate approximate­ prefer to use conventional lighting and hand ly stoichiometricaUy. The titration should pro­ stirring. Others report better results by using ceed immediately upon addition of the indicator, a visual-titration assembly consisting of a because the color of the solution fades after motor-driven stirrer, 25-mL buret, white- standing. The optimum pH of the titration is porcelain-base buret holder, and shaded in­ 10.4 or above. candescent lamp. The sample beaker is placed 2.3 Additional information on the principle near the front of the porcelain base, and the of the determination is given by Goetz and reaction is viewed diagonally downward others (1950), and by Botha and Webb (1952). through the side of the beaker and against the white background. Illumination is from behind 3. Interferences the beaker. 3.1 The salt Na2EDTA also forms stable complexes with iron, manganese, copper, lead, 5. Reagents cobalt, zinc, and nickel. Heavy-metal inter­ 5.1 Ammonium hydroxide, concentrated (sp ferences can usually be eliminated by complex- gr 0.900). ing the metals with cyanide. In the presence of 5.2 Calcium standard solution, 1.00 mL = cyanide, the procedure can be used to analyze 1.00 mg CaCO3: Suspend 1.000 g CaCO3, dried undiluted samples having iron, copper, zinc, or at 180 °C for 1.0 h, in approx 600 mL deminer- lead concentrations as high as 10 mg/L. alized water and dissolve cautiously with a min­ 3.2 The higher oxidation states of manga­ imum of dilute HCL Dilute to 1,000 mL with nese than manganese(II) react rapidly with the demineralized water. 229 230 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Eriochrome Black T indicator solution, and purple have disappeared and the solution 0.4 g/L: Dissolve 0.40 g Eriochrome Black T in is clear blue. The change in color occurs rapid­ 100 ml. demineralized water and dilute to 1 L ly; so the end point of the titration must be ap­ with 95-percent ethanol. This indicator is stable proached cautiously. for at least 2 months. The Eastman Kodak Co. reagent has been found to be satisfactory. 7. Calculations 5.4 Hydroxylamine hydrochloride solution, 30 g/L: Dissolve 30 g NH2OH-HC1 in deminer­ Hardness, alized water and dilute to 1 L. 1,000 5.5 Potassium ferrocyanide, crystals. as CaCO3 (mg/L) = X mL titrant 5.6 Sodium cyanide solution, CAUTION: mL sample NaCN is a deadly poison, and the reagent solu­ tion must be so marked, 2.5 g/100 mL: Dissolve 8. Report 2.5 g NaCN in demineralized water and dilute Report hardness, as CaCO3 (00900), as fol­ to 100 mL. lows: less than 10 mg/L, whole numbers; 10 5.7 Na^EDTA standard solution, 1.00 mL o mg/L and above, two significant figures. 1.00 mL mg CaCO3: Dissolve 3.72 g Na2EDTA-2H2O, dried overnight in a H2SO4 9. Precision desiccator, in demineralized water and dilute to 9.1 Precision for hardness for 37 samples 1,000 mL. The reagent is stable for several within the range of 3.2 to 312 mg/L may be ex­ weeks and a larger volume is usually prepared. pressed as follows: Check the titer of the reagent by titrating 25.0 mL calcium standard solution as described in ST = 0.04LY + 0.310 the procedure for sample analysis. where 6. Procedure ST = overall precision, milligrams per liter, 6.1 Pipet a volume of sample containing less and than 25 mg hardness (50.0 mL max) into a X = concentration of hardness, milligrams 150-mL beaker, and adjust the volume to ap- per liter as CaCO3. prox 50 mL. The correlation coefficient is 0.8105. 6.2 Insert the beaker in the titration 9.2 Precision for hardness for six of the 31 assembly and start the stirrer. samples expressed in terms of the percent 6.3 Add 1 mL NH2OH-HC1 solution. relative standard deviation is as follows: 6.4 Add 1 mL concentrated NH4OH. (If not tightly stoppered, it tends to lose strength, and Number of Mean Relative standard deviation (mg/L) 1 mL of weak NH4OH will not buffer the solu­ laboratories _____(percent) tion to the desired pH). 14 3.22 90 11 4.50 7 6.5 Add 2 mL NaCN solution-CAUTION: 8 50.5 3 deadly poison. The addition of NaCN may be 14 105 3 omitted if copper, zinc, lead, cobalt, and nickel 8 232 3 11 312 4 are entirely absent, and if the sample contains less than 0.25 mg Fe and 0.025 mg Mn. References 6.6 If manganese is present, add one or two small crystals of K4Fe(CN)6-3H2O. Stir and Botha, C. R., and Webb, M. M.t 1952, The versenate method wait at least 5 min until the Mn2Fe(CN)6 for the determination of calcium and magnesium in precipitates. mineralized waters containing large concentrations of 6.7 Add 2.0 mL Eriochrome Black T in­ interfering ions: Institute of Water Engineers Journal, dicator solution. v. 6. Goetz, A., Loomis, T. C., and Diehl, H., 1950, Total hard­ 6.8 Titrate with Na2EDTA standard solu­ ness in water—the stability of standard disodium tion until blue or purple swirls begin to show. dihydrogen ethylenediamine tetraacetate solutions: The end point is reached when all traces of red Analytical Chemistry, v. 22, p. 798-9. Hardness, noncarbonate, calculation

Parameter and Code: Hardness, noncarbonate 1-1344-85 (mg/L as CaCO^: 00902

1. Application hardness and average alkalinity and not from This method may be used to compute noncar­ the average of the noncarbonate hardnesses of bonate hardness for any water for which deter­ the individual samples. mined values are available for hardness and alkalinity. 7. Calculations Hardness, noncarbonate, as mg/L CaCO3 = 2. Summary of method (me/L hardness-me/L alkalinity) X 50.05 Noncarbonate hardness is computed from the hardness and alkalinity determinations 8. Report (methods 1-1340 and 1-1030 or 1-2030). No neg­ Report hardness, noncarbonate, calculated as ative values are reported. However, "negative CaCO3 (00902), concentrations as follows: less noncarbonate hardness" will counteract than 10 mg/L, whole numbers; 10 mg/L and "positive noncarbonate hardness" in a mixture above, two significant figures. of two or more waters. Hence, in all calculations of averages concerned with a mixture of waters 9. Precision for which two or more analyses are available, Precision data are not available for this noncarbonate hardness of the resulting mix- method, but reproducibility should be com­ tures must be computed from the average parable to that of the individual determinations. 231

Iodide, colorimetric, ceric-arsenious oxidation

Parameter and Code: Iodide, dissolved, 1-1371-85 (mg/L as I): 71865

1. Application nitric acid at step 6.1 in the procedure. The This method may be used to determine iodide nitric acid should be aerated to remove nitrogen in fresh water and brines containing from 0.001 oxides. to 0.060 mg/L of iodide. Greater concentrations need to be reduced by dilution; however, sam­ 4. Apparatus ples containing concentrations greater than 1 4.1 Stirring rods, glass. mg/L need to be analyzed by the bromine ox­ 4.2 Water bath, constant-temperature idation method (method 1-1370). (30±0.5°C). 4.3 Spectrometer for use at 450 nm. 2. Summary of method 4.4 Refer to manufacturer's manual to op­ This method is based on the catalytic effect timize instrument. of iodide on the ceric-arsenious oxidation reac­ tion in acid solution. In the presence of a small 5. Reagents amount of iodide, the reaction follows first-order 5.1 Arsenious acid standard solution, 0.37V reaction-rate kinetics—and at a given tempera­ H3AsO3: Add 14.84 g primary standard As2O3 ture and for a given reaction time, the extent to 500 mL demineralized water in a 1,000-mL of reduction of eerie ion is directly proportional beaker. Next, add slowly 28 mL concentrated to the iodide concentration. The reaction may H2SO4 (sp gr 1.84); stir and warm the mixture be stopped completely at any time by the addi­ until the As2O3 is dissolved. Cool, transfer to tion of silver ion. Photometric measurement of a 1,000-mL volumetric flask, and dilute to the absorbance of the solution permits evalua­ volume with demineralized water. Add a small tion of the extent of the reaction (Mitchell, piece of metallic arsenic to stabilize the solution. 1966). 5.2 Ceric sulfate standard solution, O.IN Ce(HS04)4: Dissolve 52.80 g anhydrous 3. Interferences Ce(HSO4)4 in 600 mL 2.5M H2SO4 contained in 3.1 Most substances normally present in a 1000-mL volumetric flask. Warm the mixture natural water do not interfere. and stir occasionally until a clear solution is ob­ 3.2 Low values for iodide may result if the tained. Cool and dilute to volume with 2.5M reaction test tubes are not clean. Rinsing each H2SO4. sample tube with hydrochloric acid, followed by 5.3 Iodide standard solution I, 1.00 mL = deionized water immediately before use, 0.100 mg I"1: Dissolve 0.1308 g KI crystals, removes possible contaminants. dried overnight in a sulfuric acid desiccator, in 3.3 Bromide ion does not interfere, and any demineralized water and dilute to 1,000 mL. substance that oxidizes iodide to iodine has no 5.4 Iodide standard solution II, 1.00 mL - effect on the reaction. 0.010 mg I'1: Dilute 100 mL iodide standard 3.4 Certain phosphate compounds used in solution I to 1,000 mL with demineralized water treatment, such as Calgon, have an in­ water. hibiting effect on the reaction. This effect can 5.5 Iodide standard solution III, 1.00 be eliminated by adding 3 drops concentrated mL = 0.0001 mg I"1: Dilute 10.0 mL iodide 233 234 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS standard solution II to 1,000 mL with 6.8 Measure the absorbance of each blank, demineralized water. standard, and sample at 450 nm, using demin­ 5.6 Silver nitrate solution, 0.10 g/L: Dissolve eralized water as a reference. 0.10 g AgNO3 in 1 L demineralized water. Store in a dark bottle. 7. Calculations 5.7 Sulfuric acid, 2.5M: Cautiously add 139 7.1 Construct an analytical curve by plot­ mL concentrated H2SO4 (sp gr 1.84) to ting the ratio AJAC against milligrams of demineralized water, cool, and dilute to 1 L. iodide on semilog paper (As = absorbance of standard and Ac = absorbance of control). 6. Procedure 7.2 From the curve, determine the milli­ 6.1 Pipet a volume of sample containing less grams of iodide corresponding to the absorb­ than 0.0012 mg I"1 (20.0 mL max) into a 23-mm ance ratio obtained for each sample. absorption cell. 7.3 Determine iodide concentration in milli­ 6.2 Prepare a demineralized water blank to grams per liter as follows: be used as a control and sufficient standards containing less than 0.0012 mg I'1 in 23-mm I-1 (mg/L) = X mg I'1 absorption cells. mL sample 6.3 Dilute each sample, blank, and standard to 20.0 mL with demineralized water; add 0.5 8. Report mL concentrated H2SO4 to each and mix. Report iodide, dissolved (71865), concentra­ 6.4 Add 1.0 mL H3AsO3 standard solution tions as follows: less than 0.1 mg/L, three to each absorption cell and mix. decimals; 0.1 mg/L and above, two significant 6.5 Place all absorption cells in a constant- figures. temperature bath at 30 °C. Allow 30 to 45 min for the contents to reach temperature 9. Precision equilibrium. Precision expressed in terms of the percent 6.6 At zero time, add 1.0 mL Ce(HSO4)4 relative standard deviation is as follows: standard solution (temperature equilibrated) and miy. Number of Mean Relative standard deviation 6.7 After exactly 10 min add, with stirring, laboratories _____(percent)_____ 1 drop (0.05 mL) AgNO3 solution (NOTE 1). 3 0.023 91 3 .034 91 NOTE 1. The addition of AgNO3 solution 3 .117 55 may be omitted if the eerie sulfate solution is added at intervals of 30 sec or longer and the Reference absorbance of each sample, blank, and stand­ Mitchell, C. G., 1966, Semimicroanalytical method for the ard measured exactly 10.0 min after the addi­ determination of iodide in water: U.S. Geological tion of the Ce(HSO4)4 solution. Survey Water-Supply Paper 1822, p. 77-83. Iodide, colorimetric, ceric-arsenious oxidation, automated-segmented flow

Parameter and Code: Iodide, dissolved, 1-2371-85 (mg/L as I): 71865

1. Application Absorption cell ——— 15 mm This method may be used to determine iodide Wavelength ————— 410 run in fresh water and brines containing from 0.001 Cam —————————— 30/h (2/1) to 0.060 mg/L of iodide. Greater concentrations need to be reduced by dilution; however, sam­ 5. Reagents ples containing concentrations greater than 1 5.1 Arsenious acid solution, 2.782 g/L: Add mg/L need to be analyzed by the bromine oxi­ 2.782 g primary standard As2O3 to approx dation method (method 1-1370). 500 mL demineralized water in a 1,000-mL volumetric flask. Slowly add 3 mL concen­ 2. Summary of method trated H2SO4 (sp gr 1.84). Warm the mixture The method is based on the catalytic effect until the As2O3 is dissolved. Cool and dilute of iodide on the ceric-arsenious oxidation reac­ to 1,000 mL with demineralized water. Add a tion in acid solution. In the presence of a small small piece of metallic arsenic to stabilize the amount of iodide, the reaction follows first-order solution. reaction-rate kinetics—and at a given tempera­ 5.2 Ceric sulfate solution, 1.584 g/L: Add 600 ture and for a given reaction time, the extent mL 2.5M H2SO4 and 1.584 g anhydrous of reduction of eerie ion is directly proportional Ce(HSO4)4 to a 1,000-mL volumetric flask. to the iodide concentration. Photometric meas­ Warm the mixture and stir occasionally until urement of the absorbance of the solution per­ a clear solution is obtained. Cool and dilute to mits evaluation of the extent of the reaction volume with 2.5Af H2SO4. (MitcheU, 1966). 5.3 Iodide standard solution I, 1.00 mL = 0.100 mg I"1: Dissolve 0.1308 g KI crystals, 3. Interferences dried overnight in a sulfuric acid desic­ 3.1 Most substances normally present in cator, in demineralized water and dilute to natural water do not interfere. 1,000 mL. 3.2 Bromide ion does not interfere. 5.4 Iodide standard solution II, 1.00 mL = 3.3 Low iodide values will be obtained if the 0.010 mg I"1: Dilute 100 mL iodide standard pH of the water samples is less than 3 or if the solution I to 1,000 mL with demineralized iron concentration exceeds 500 jxg/L. water. 5.5 Iodide standard solution III, 1.00 mL = 4. Apparatus 0.0005 mg I-1: Dilute 50.0 mL iodide standard 4.1 Technicon AutoAnalyzer II, consisting solution II to 1,000 mL with demineralized of a sampler, proportioning pump, cartridge water. manifold, colorimeter, voltage stabilizer, re­ 5.6 Iodide working standards: Prepare a corder, printer, and heating bath. blank and 500 mL each of a series of iodide 4.2 With this equipment the following working standards by appropriate quantitative operating conditions have been found satisfac­ dilution of the iodide standard solution III as tory for the range from 0.001 to 0.060 mg/L: follows: 235 236 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Iodide standard solution III Iodide concentration (mL) (mg/L) on the recorder, adjust the STD CAL control un­ til the flat portion of the peak reads full scale 00 0.000 2.0 .002 5.0 .005 7. Calculations 10.0 .010 7.1 Prepare an analytical curve by plotting 20.0 .020 40.0 .040 the height of each peak versus its respective 60.0 .060 iodide concentration. 7.2 Compute the iodide concentration of 5.6 Sulfuric acid, 2.5M: Cautiously add 139 each sample by comparing its peak height to the mL concentrated H2SO4 (sp gr 1.84) to demin- analytical curve. Any baseline drift that may eralized water, cool, and dilute to 1 L. occur must be taken into account when com­ puting the height of a sample or standard peak. 6. Procedure 6.1 Set up manifold (fig, 27). 6.2 Allow colorimeter and recorder to warm 8. Report up for at least 30 min. Report iodide, dissolved (71865), concentra­ 6.3 Adjust the baseline to read zero scale divi­ tions as follows: less than 0.1 mg/L, three sion on the recorder with all reagents, but with decimals; 0.1 mg/L and above, two significant demineralized water in the sample tuba figures. 6.4 Place a complete set of standards and a blank In the first positions of the first sample 9. Precision tray, beginning with the most concentrated stand- Precision data are not available for this method. aid. Place individual standards of differing concen­ trations in approximately every eighth position of the remainder of this and subsequent sample Reference trays. Fill remainder of each tray with samples. Mitchell, C. G., 1966, Semimicroanalytical method for the 6.5 Begin analysis. When the peak from the determination of iodide in water: U.S. Geological most concentrated working standard appears Survey Water-Supply Paper 1822, p. 77-83.

He; rting bath, 50°C O.OSOin Air Co 1 No. 157-0222 0.32 mL/min 22-turn coil Sample rrainn^ (OOOO) ^ 0.040in > » 1 0.60 mL/min -o O.OSOin Sulfuric acid 0.32 mL/min Sampler < O.OSOin Arsenious acid 307 h 0.32 mL/min 3/1 cam Colorimeter Ceric sulfate 410 nm x*aste O.OSOin 15- mm cell/ To sampler 4 0.32 mL/min wash O.OS6in Water T 1.20 mL/min -s.pi receptac:le 0.045in Waste 0.80 mL/min Recorder Piroportioning pump

Figure 27.—Iodide, ceric-arsenious oxidation manifold Iodide, titrimetric, bromine oxidation

Parameter and Code: Iodide, dissolved 1-1370-85 (mg/L as I): 71865

1. Application 5.2 Bromine water, saturated: Add to ap- This method may be used to analyze any prox 250 mL demineralized water slightly more natural or treated water or brine containing at liquid Br2 than will dissolve when mixed. Store least 1.0 mg/L of iodide, from which interfering in a glass-stoppered, actinic-glass bottle. substances have been removed. 5.3 Calcium oxide, CaO, anhydrous powder. 5.4 Methyl red indicator solution, 0.01 g/100 2. Summary of method mL: Dissolve 0.01 g water-soluble methyl red Iodide in a buffered solution is oxidized by in 100 mL demineralized water. bromine to iodate; the excess bromine is subse­ 5.5 Potassium fluoride, KF-2H2O, crystals. quently removed by adding sodium formate 5.6 Potassium iodide, crystals, IO3~1-free: (Kolthoff and others, 1969): The KI can be tested for lO^1 by dissolving 0.1 g in 5 mL water, acidifying with 1 or 2 drops 3Br 6HBr concentrated H2SO4 (sp gr 1.84), and adding 2 or 3 mL starch indicator. Immediate appearance Iodine equivalent to the iodate is then liberated of a blue color indicates the presence of lOjj1; by addition of potassium iodide to an acid slow color formation is due to atmospheric solution: oxidation. 5.7 Sodium acetate solution, 165 g/L: Dis­ 6H+1-3I2 + 3H20 solve 274 g CH3COONa-3H2O in demineralized Finally the liberated iodine is titrated with water and dilute to 1 L. standard thiosulfate solution with starch used 5.8 Sodium formate solution, 50 g/100 mL: as the indicator: Dissolve 50 g HCOONa in hot demineralized water and dilute to 100 mL. Prepare fresh daily. 5.9 Sodium thiosulfate solution, 0.10JV: Dissolve 25 g Na2S2O3-5H2O in carbon diox­ 3. Interferences ide-free demineralized water. Add 1 g Na2CO3 Iron, manganese, and organic material inter* and dilute to 1 L. fere with the basic reactions of the method, but 5.10 Sodium thiosulfate standard solution, their interferences are removed by preliminary Q.QIQN; Dilute 100 mL O.lOJVNa^C^ solution treatment with calcium oxide. to 950 mL with carbon dioxide-free demineral­ ized water and standardize against KIO3 as 4. Apparatus follows: Dry approx 0.5 g KIO3 for 2 h at 180 °C. 4.1 Buret, 10-mL capacity. Cool and dissolve 0.3567 g in demineralized 4.2 Flasks, 250-mL capacity. water; dilute to 1,000 mL. Pipet 25.0 mL of the KIO3 solution into a 250 mL flask; then add 5. Reagents successively 75 mL demineralized water and 0.5 5.1 Acetic acid, 2.2M: Mix 125 mL glacial g KI crystals. After solution is complete, add CH3COOH (sp gr 1.06) with demineralized 10 mL 3.6M H2SO4. Allow the stoppered flask water and dilute to 1 L. to stand 5 min in the dark, then titrate with 237 238 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS standard Na2S2O3 solution, adding 2 to 3 mL 6.11 Titrate the liberated I2 with standard starch indicator solution as the end point is ap­ Na282O3 solution, adding 2 to 3 mL starch in­ proached (light-straw color). dicator solution as the end point is approached 0.25 (light-straw color). Disregard a return of the Normality of Na2S2O3 blue color after the end point has been reached. mL Na2S2O3 7. Calculations 5.11 Starch indicator solution, stable or 1,000 "thyodene," powdered (Fisher No. T138 or I'1, mg/L = —————— X 21.15 X equivalent). mL sample 5.12 Sulfuric acid, 3.6M: Cautiously add 200 mL concentrated H2SO4 (sp gr 1.84) to demin- [(mL titrant—mL blank) X AT] eralized water, cool, and dilute to 1 L. where N = normality of standard thiosulfate 6. Procedure solution, 6.1 Remove soluble iron, manganese, and organic matter by adding a slight excess of CaO and to approx 400 mL of sample; shake, let stand 21.15 = equivalent weight of iodide. approx 1 h, and filter through a dry, moderate­ ly retentive filter paper. Discard the first 75 mL 8. Report of filtrate. Report iodide, dissolved (71865), concentra­ 6.2 Pipet a volume of the filtrate containing tions as follows: less than 10 mg/L, one decimal; less than 5.0 mg I'1 (100.0 mL max) into a 10 mg/L and above, two significant figures. 250-mL flask, and adjust the volume to 100 mL. 6.3 Prepare a blank of 100 mL demineralized 9. Precision water and carry it through the procedure along Single-operator precision of this method with the sample. (American Society for Testing and Materials, 6.4 Add 1 drop methyl red indicator solution 1984) may be expressed as follows: and make the solution just acid with 3.6M H2SO4. S0 = 0.009X 6.5 Add 15.0 mL CH3COONa solution and where 5.0 mL 2.2M CH3COOH. 6.6 Add sufficient Br2 water to produce a S0 = single-operator precision, milligrams per light-yellow color, mix, and allow to stand 5 min. liter, 6.7 Reduce the excess Br2 by adding and HCOONa solution until the yellow tinge in the X= concentration of iodide, milligrams per sample disappears; then add 1 mL excess. liter. 6.8 Wash the sides of the flask with a small amount of water, and expel Br2 vapors with a References syringe and a glass tube inserted through the mouth of the flask. American Society for Testing and Materials, 1984, Annual 6.9 If any iron precipitates at this point, add book of ASTM standards, section 11, water: Phila­ delphia, v. 11.01, p. 476-84. 0.5 g KF-2H2O. Kolthoff, I. M., Sandell, E. B., Meehan, E. J., and Brucken- 6.10 Add approx 1 g KI and 10 mL 3.6M stein, S., 1969, Quantitative Chemical Analysis (4th ed): H2SO4; mix and let stand 5 min in the dark. New York, Macmillan, 1199 p. Iron, atomic absorption spectrometric, direct

Parameters and Codes: Iron, dissolved, 1-1381-85 (/ig/L as Fe): 01046 Iron, total recoverable, 1-3381-85 (^g/L as Fe): 01045 Iron, suspended recoverable, 1-7381-85 fcg/L as Fe): 01044 Iron, recoverable-from-bottom-material, dry wt 1-5381-85 (j*g/g as Fe): 01170

1. Application antimony, arsenic, vanadium, boron, and 1.1 This method may be used to analyze water molybdenum (1 X 105 j*g/L each) do not inter­ and water-suspended sediment containing at fere. Greater concentrations of each constituent least 10 /ig/L of iron. Sample solutions contain­ were not investigated. ing more than 1,000 figIL need either to be diluted or to be read on a less expanded scale. 4. Apparatus 1.2 Suspended recoverable iron is calculated 4.1 Atomic absorption spectrometer by subtracting dissolved iron from total equipped with electronic digital readout and recoverable iron. automatic zero and concentration controls. 1.3 This method may be used to analyze bot­ 4.2 Refer to the manufacturer's manual to tom material containing at least 1 pglg of iron. optimize instrument for the following: Prepared sample solutions containing more Grating ———————— Ultraviolet than 1,000 jig/L need either to be diluted or to Wavelength ————— 248.3 nm be read on a less expanded scale. Source (hollow-cathode 1.4 Total recoverable iron in water-sus­ lamp) ———————— Iron pended sediment needs to undergo preliminary Oxidant ———————— Air digestion-solubilization by method 1-3485, and Fuel —————————— Acetylene recoverable iron in bottom material needs to Type of flame ———— Oxidizing undergo preliminary digestion-solubilization by 4.3 Different burners may be used according method 1-5485 before being determined. to manufacturers' instructions.

2. Summary of method 5. Reagents 2.1 Iron is determined by atomic absorption 5.1 Iron standard solution /, 1.00 mL = 400 spectrometry by direct aspiration of the sam­ /ig Fe: Weigh 0.400 g analytical grade Fe wire ple solution into an air-acetylene flame. that has been cleaned in dilute HC1, rinsed, and 2.2 The procedure may be automated by the dried. Dissolve in 5 mL concentrated HNO3 (sp addition of a sampler and either a strip-chart gr 1.41), warming if necessary, and dilute to recorder or a printer or both. 1,000 mL with demineralized water. 5.2 Iron standard solution //, 1.00 mL = 3. Interferences 4.00 /ig Fe: Dilute 10.0 mL iron standard solu­ Individual concentrations of sodium, potas­ tion I and 1 mL concentrated HNO3 (sp gr 1.41) sium, chloride, and sulfate (5,000 mg/L each), to 1,000 mL with demineralized water. This calcium and magnesium (1,000 mg/L each), standard is used to prepare working standards nitrate (100 mg/L), chromium, manganese, at time of analysis. cobalt, nickel, copper, zinc, silver, cadmium, tin, 5.3 Iron working standards: Prepare a series lead, lithium, mercury, selenium, aluminum, of at least six working standards containing 239 240 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS from 10 to 1,000 /tg/L of iron by appropriate jig/L, nearest 10 /*g/L; 100 /*g/L and above, two dilution of iron standard solution II with acidi­ significant figures. fied water. Prepare fresh daily. 8.2 Report iron, recoverable-from-bottom- 5.4 Water, acidified'. Add 1.5 mL concen­ material (01170), concentrations as follows: less trated HNO3 (sp gr 1.41) to 1 liter of deminer- than 100 /ig/g, nearest microgram per gram; 100 alized water. jig/g and above, two significant figures.

6. Procedure 9. Precision Aspirate the blank (acidified water) to set the 9.1 Precision for dissolved iron for 26 sam­ automatic zero control. Use the automatic con­ ples within the range of 38 to 996 jig/L may be centration control to set the concentrations of expressed as follows: standards. Use at least six standards. Calibrate the instrument each time a set of samples is ST = 0.066X + 18.58 analyzed and check calibration at reasonable intervals. where ST — overall precision, micrograms per liter, 7. Calculations and 7.1 Determine the micrograms per liter of X = concentration of iron, micrograms per dissolved or total recoverable iron in each sam­ liter. ple solution from the digital display or printer The correlation coefficient is 0.8305. while aspirating each sample. Dilute those sam­ 9.2 Precision for dissolved iron for six of the ples containing iron concentrations that exceed 26 samples expressed in terms of the percent the working range of the method and multiply relative standard deviation is as follows: by the proper dilution factors. Number of Relative standard deviation 7.2 To determine micrograms per liter sus­ laboratories _____(percent)_____ pended recoverable iron, subtract dissolved- 18 38 42 iron concentration from total-recoverable-iron 29 110 25 concentration. 22 277 12 16 445 10 7.3 To determine micrograms per gram of 33 750 8 iron in bottom-material samples, first determine 13 996 6 the micrograms per liter of iron as in paragraph 7.1; then 9.3 It is estimated that the percent relative standard deviation for total recoverable and suspended recoverable iron and recoverable iron mL of original digest in bottom material will be greater than that Fe X reported for dissolved iron. _____1,000____ Fe (/tg/g) = 9.4 Precision for total recoverable iron ex­ wt of sample (g) pressed in terms of percent relative standard deviation for two water-suspended sediment 8. Report mixtures is as follows:

Number of Relative standard deviation 8.1 Report iron, dissolved (01046), total- laboratories (MO/L) _____(percent)_____ recoverable (01045), and suspended-recoverable 24 7376 49 (01044), concentrations as follows: less than 100 19 7680 38 Iron, atomic emission spectrometric, ICP

Parameter and Code: Iron, dissolved, 1-1472-85 (/xg/L as Fe): 01046

2. Summary of method method utilizing an induction-coupled argon Iron is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP.

241

Iron, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Iron, total, 1-5473-85 (mg/kg as Fe): none assigned Iron, total, 1-5474-85 (mg/kg as Fe): none assigned

2. Summary of method 1-5473, metals, major, total-in-sediment, atomic 2.1 A sediment sample is dried, ground, and absorption spectrometric, direct. homogenized. The sample is then treated and 2.1.2 The sample is digested with a combina­ analyzed by one of the following techniques. tion of nitric, hydrofluoric, and perchloric acids 2.1.1 The sample is fused with a mixture of in a Teflon beaker heated on a hotplate at lithium metaborate and lithium tetraborate in a 200 °C. Iron is determined on the resulting solu­ graphite crucible in a muffle furnace at 1000 °C. tion by atomic absorption spectrometry. See The resulting bead is dissolved in acidified, boil­ method 1-5474, metals, major and minor, total- ing, demineralized water, iron is then determined in-sediment, atomic absorption spectrometric, by atomic absorption spetrometry. See method direct. 243

Lead, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Lead, dissolved, 1-1400-85 fcig/L as Pb): 01049 Lead, total recoverable, I-3400-85 (/*g/L as Pb): 01051 Lead, suspended recoverable, I -7400 -85 (pg/L as Pb): 01050

1. Application 4.2 Refer to the manufacturer's manual to 1.1 This method may be used to analyze water optimize instrument for the following: and water-suspended sediment containing from Grating ———————— Ultraviolet 5 to 100 /Ag/L of lead. Sample solutions contain­ Wavelength ————— 283.3 nm ing more than 100 jig/L need either to be diluted Source (hollow-cathode prior to chelation-extraction or to be analyzed lamp or electrodeless- by the atomic absorption spectrometric direct discharge lamp) — Lead method. Oxidant ———————— Air 1.2 Suspended recoverable lead is calculated Fuel —————————— Acetylene by subtracting dissolved lead from total recov­ Type of flame ———— Oxidizing erable lead. 4.3 Different burners may be used according 1.3 Total recoverable lead in water-sus­ to manufacturers' instructions. pended sediment needs to undergo a prelimi­ nary digestion-solubilization by method 1-3485 5. Reagents before being determined. 5.1 Ammonium pyrrolidine dithiocarbamate 1.4 If the iron concentration of the sample solution, 1 g/100 mL: Dissolve 1 g APDC in 100 exceeds 25,000 /ig/L, determine lead by the mL demineralized water. Prepare fresh daily. atomic absorption spectrometric direct method. 5.2 Citric acid-sodium citrate buffer solution: Dissolve 126 g citric acid monohydrate and 44 2. Summary of method g sodium citrate dihydrate in demineralized Lead is determined by atomic absorption water and dilute to 1 L with demineralized spectrometry following chelation with am­ water. See NOTE 3 before preparation. monium pyrrolidine dithiocarbamate (APDC) 5.3 Lead standard solution /, 1.00 mL = 200 and extraction with methyl isobutyl ketone /*g Pb: Dissolve 0.2000 g Pb shot in a minimum (MIBK). The extract is aspirated into an air- of dilute HNO3. Heat to increase rate of dissolu­ acetylene flame of the spectrometer (Fishman tion. Add 10 mL concentrated HNO3 (sp gr 1.41) and Midgett, 1968). and dilute to 1,000 mL with demineralized water. 5.4 Lead standard solution II, 1 mL = 2.00 3. Interferences /ig Pb: Dilute 10.0 mL lead standard solution Concentrations of iron greater than 25,000 I and 1 mL concentrated HNO3 (sp gr 1.41) to /ig/L interfere by suppressing the lead ab­ 1,000 mL with demineralized water. This stand­ sorption. ard is used to prepare working standards at the time of analysis. 4. Apparatus 5.5 Methyl isobutyl ketone (MIBK). 4.1 Atomic absorption spectrometer 5.6 Potassium hydroxide, 10 M: Dissolve 56 equipped with electronic digital readout and g KOH in demineralized water, cool, and dilute automatic zero and concentration controls. to 100 mL. 245 246 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.7 Potassium hydroxide, 2.5M: Dissolve 14 aspirating each sample. Dilute those samples g KOH in demineralized water and dilute to 100 containing lead concentrations that exceed the mL (NOTE 1). working range of the method; repeat the chela- NOTE 1. Alternatively, a 2.5M NH4OH solu­ tion-extraction and multiply by the proper dilu­ tion may be used Add 167 mL concentrated tion factors. NH4OH (sp gr 0.90) to 600 mL demineralized 7.2 lb determine the micrograms per liter of water. Cool, and dilute to 1 L. suspended recoverable lead, subtract dissolved- 5.8 Water, acidified: Add 1.5 mL concentrated lead concentration from total-recoverable-lead HNO3 (sp gr 1.41) to 1 L of demineralized water. concentration,

6. Procedure 8. Report 6.1 Clean all glassware used in this determin­ Report lead (Pb), dissolved (01049), total- ation with warm, dilute HNO3 (1+9) and rinse recoverable (01051), and suspended-recoverable with demineralized water immediately before use. (01050), concentrations as follows: 5 to 10 /ig/L, 6.2 Pipet a volume of sample solution con­ nearest microgram per liter; 10 /ig/L and above, taining less than 10.0 fig Pb (100 mL max) into two significant figures. a 200-mL volumetric flask and adjust the volume to approx 100 mL. 9. Precision 6.3 Prepare a blank of acidified water and suf­ 9.1 Precision for dissolved lead for 23 samples ficient standards, and adjust the volume of each within the range of 3.8 to 73 /ig/L may be ex­ to approx 100 mL with acidified water. pressed as follows: 6.4 With a pH meter, adjust the pH of each solution to 2.4 with 2.5M KOH (NOTES 2 and ST = 0.23 IX + 0.458 3). Shake for 3 min. NOTE 2. For water-suspended sediment sam­ where ples that have been digested, add 1 to 2 mL 10M ST = overall precision, micrograms per liter, KOH or concentrated NH4OH (sp gr 0.90) before and pH adjustment. X = concentration of lead, micrograms per NOTE 3. If an automated titration system is liter. used to adjust the pH, add 2.5 mL citric acid- The correlation coefficient is 0.8702. sodium citrate buffer solution prior to pH adjust­ 9.2 Precision for dissolved lead for five of the ment. This will prevent over-shooting the end 23 samples expressed in terms of the percent point in poorly buffered samples. relative standard deviation is as follows: 6.5 Add 2.5 mL APDC solution and mix. Number of Relative standard deviation 6.6 Add 10.0 mL MIBK and shake vigorous­ frO/U _____(percent)_____ ly for 3 min. 6 3.83 76 6.7 Allow the layers to separate and add 7 4.00 38 demineralized water until the ketone layer is com­ 14 13.9 30 pletely in the neck of the flask. 14 26.5 29 6.8 Aspirate the ketone layer within 1 h. 17 72.9 28 Aspirate the ketone layer of the blank to set the 9.3 It is estimated that the percent relative automatic zero control Use the automatic con­ standard deviation for total recoverable and centration control to set the concentrations of suspended recoverable lead will be greater than standards. Use at least six standards. Calibrate that reported for dissolved lead. the instrument each time a set of samples is analyzed and check calibration at reasonable intervals. Reference Fishman, M. J., and Midgett, M. R, 1968, Extraction tech­ 7. Calculations niques for the determination of cobalt, nickel, and lead 7.1 Determine the micrograms per liter of dis­ in fresh water by atomic absorption, in Trace inorganics solved or total recoverable lead in each sample in water American Chemical Society, Advances in from the digital display or printer while Chemistry Series, no. 73, p. 230-5. Lead, atomic absorption spectrometric, direct

Parameters and Codes: Lead, dissolved, 1-1399-85 (/xg/L as Pb): 01049 Lead, total recoverable, (-3399-85 0*g/L as Pb): 01051 Lead, suspended recoverable, I-7399-85 (^g/L as Pb): 01050 Lead, recoverable-from-bottom-material, dry wt, I-5399-85 0*g/g as Pb): 01052

1. Application copper, zinc, cobalt, and chromium (10,000 /tg/L) 1.1 This method may be used to analyze water do not interfere. Higher concentrations of each and water-suspended sediment containing at constituent were not investigated. least 100 /ig/L of lead. Sample solutions contain­ ing more than 4,000 j*g/L need either to be 4. Apparatus diluted or to be read on a less expanded scale. 4.1 Atomic absorption spectrometer Sample solutions containing less than 100 j*g/L equipped with electronic digital readout and need to be analyzed by the atomic absorption automatic zero and concentration controls. spectrometric delation-extraction method, pro­ 4.2 Refer to the manufacturer's manual to viding that the interference limits discussed in optimize instrument for the following: that method are not exceeded. Grating ———————— Ultraviolet 1.2 Suspended recoverable lead is calculated Wavelength ————— 283.3 nm by subtracting dissolved lead from total recov­ Source (hollow-cathode erable lead. or electrodeless-dis- 1.3 This method may be used to analyze bot­ charge lamp) ——— Lead tom material containing at least 10 /*g/g of lead. Oxidant -——————— Air Prepared sample solutions containing more Fuel ——!——————— Acetylene than 4,000 jig/L need either to be diluted or to Type of flame ———— Slightly oxidizing be read on a less expanded scale. 4.3 The 100-mm (4-in.), flathead, single-slot 1.4 Total recoverable lead in water-sus­ burner allows a working range of 100 to 4,000 pended sediment needs to undergo preliminary Mg/L. Different burners may be used according digestion-solubilization by method 1-3485, and to manufacturers' instructions. recoverable lead in bottom material needs to undergo preliminary digestion-solubilization by 5. Reagents method 1-5485 before being determined. 5.1 Lead standard solution /, 1.00 mL = 200 ^g Pb: Dissolve 0.2000 g Pb shot in a minimum 2. Summary of method of dilute HNO3. Heat to increase rate of dis­ Lead is determined by atomic absorption solution. Add 10 mL concentrated HNO3 (sp gr spectrometry by direct aspiration of the sam­ 1.41) and dilute to 1,000 mL with demineralized ple solution into an air-acetylene flame. water. 5.2 Lead standard solution II, 1.00 mL = 20 3. Interferences jig Pb: Dilute 100.0 mL lead standard solution Individual concentrations of sodium (9,000 I and 1 mL concentrated HNO3 (sp gr 1.41) to mg/L), potassium (9,000 mg/L), calcium (4,000 1,000 mL with demineralized water. mg/L), magnesium (4,000 mg/L), nitrate (900 5.3 Lead working standards: Prepare a series mg/L), iron (4 X 106 /tg/L), and cadmium, nickel, of at least six working standards containing 247 248 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS from 100 to 4,000 /tg/L of lead by appropriate than 100 /tg/g, nearest 10 /*g/g; 100 /*g/g and dilution of lead standard solution II with acidi­ above, two significant figures. fied water. Prepare fresh daily. 5.4 Water, acidified: Add 1.5 mL concen­ 9. Precision trated HNO3 (sp gr 1.41) to 1 L of demineral- 9.1 Precision for dissolved lead for 15 sam­ ized water. ples within the range of 6.70 to 80.3 /*g/L (NOTE 1) may be expressed as follows: 6. Procedure Aspirate the blank (acidified water) to set the ST = 0.498X-0.509 automatic zero control. Use the automatic con­ centration control to set the concentrations of standards. Use at least six standards. Calibrate ST — overall precision, micrograms per liter, the instrument each time a set of samples is and analyzed and check calibration at reasonable in­ X= concentration of lead, micrograms per tervals. liter. The correlation coefficient is 0.9118. 7. Calculations NOTE 1. Precision data are given for lead con­ 7.1 Determine the micrograms per liter of centrations below the reporting level of 100 dissolved or total recoverable lead in each sam­ pg/L. Samples were not available that contained ple solution from the digital display or printer greater lead concentrations; however, precision while aspirating each sample. Dilute those sam­ should improve at greater concentrations. ples containing lead concentrations that exceed 9.2 Precision for dissolved lead for four of the working range of the method and multiply the 15 samples expressed in terms of the per­ by the proper dilution factors. cent relative standard deviation is as follows: 7.2 To determine micrograms per liter sus­ pended recoverable lead, subtract dissolved-lead Number of Mean Relative standard deviation concentration from total-recoverable-lead con­ laboratories frO/L) ______(percent)_____ centration. 7 6.70 75 , 7.3 To determine micrograms per gram of 8 25.5 56 lead in bottom-material samples, first determine 13 46.4 51 the micrograms per liter of lead as in paragraph 18 80.3 55 7.1; then 9.3 It is estimated that the percent relative standard deviation for total recoverable and mL of original digest suspended recoverable lead and for recoverable /ig/L PbX lead in bottom material will be greater than that Pb ____1.000____ wt of sample (g) reported for dissolved lead. 9.4 Precision for total recoverable lead ex­ pressed in terms of percent relative standard 8. Report deviation for two water-suspended sediments is 8.1 Report lead, dissolved (01049), total-re­ as follows: coverable (01051), and suspended-recoverable Number of Mean Relative standard deviation (01050), concentrations to the nearest 100 /xg/L. laboratories WL) _____(percent)_____ 8.2 Report lead, recoverable-from-bottom- 9 44.1 54 material (01052), concentrations as follows: less 7 51.9 38 Lead, atomic absorption spectrometric, graphite furnace

Parameter and Code: Lead, dissolved, 1-1401-85 G*g/L as Pb): 01049

1. Application form reduces the effects of many interferences. 1.1 This method may be used to determine Calcium (25 mg/L)t magnesium (8 mg/L), sodium lead in low ionic-strength water and precipita­ (20 mg/L), sulfate (34 mg/L), and chloride (25 tion. With deuterium background correction mg/L) do not interfere. Higher concentrations and a 20-/iL sample, the method is applicable of these constituents were not investigated. in the range from 0.3 to 20 /*g/L. With Zeeman 3.2 Precipitation samples usually contain background correction and a 20-piL sample, the very low concentrations of lead. Special precau­ method is applicable in the range from 0.5 to tionary measures must be employed during 50 /ig/L. Sample solutions that contain lead con­ both sample collection and laboratory deter­ centrations exceeding the upper limits must be mination to prevent contribution from con­ diluted or preferably be analyzed by the atomic tamination. absorption spectrometric direct or chelation- extraction method, or by the atomic emission 4. Apparatus spectrometric ICP method. 4.1 Atomic absorption spectrometer, for use 1.2 The analytical range and detection limits at 283.3 run and equipped with background cor­ can be increased or possibly decreased by vary­ rection, digital integrator to quantitate peak ing the volume of sample injected or the in­ areas, graphite furnace with temperature pro* strumental settings. Purification of reagents grammar, and automatic sample injector. The and use of ASTM Type 1 water (Method programmer must have high-temperature ramp­ D-1193, American Society for Testing and ing and stopped-flow capabilities. Materials, 1984) may result in lower detection 4.1.1 Refer to the manufacturer's manual to limits. optimize instrumental performance. The analytical ranges reported in paragraph 1.1 are 2. Summary of method for a 20-/*L sample with 5 pL of matrix modifier Lead is determined by atomic absorption (NOTE 1). spectrometry in conjunction with a graphite fur­ NOTE 1. A 20-jiL sample generally requires 30 nace containing a graphite platform (Hinder- s to dry. Samples that have a complex matrix berger and others, 1981). A sample is placed on may require a longer drying and charring time. the graphite platform and a matrix modifier is 4.1.2 Graphite furnace, capable of reaching added. The sample is then evaporated to dry- temperatures sufficient to atomize the element ness, charred, and atomized using high-tempera­ of interest. Warning: dial settings frequently ture ramping. The absorption signal generated are inaccurate and newly conditioned furnaces during atomization is recorded and compared require temperature calibration. with standards. 4.1.3 Graphite tubes and platforms. Pyrolyt- ically coated graphite tubes and solid pyrolytic 3. Interferences graphite platforms are recommended. 3.1 Interferences in low ionic-strength sam­ 4.2 Lab ware. Many trace metals at very ples, such as precipitation, normally are quite low concentrations have been found to sorb low. In addition, the use of the graphite plat­ very rapidly to glassware. To preclude this, 249 250 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS fluorinated ethylene propylene (FEP) or Teflon chelation with ammonium pyrrolidine dithiocar- labware may be used. Alternately, glassware, bamate (APDC) and extraction with methyl particularly flasks and pipets, may be treated isobutyl ketone (MIBK) (NOTE 3). Analyze 20 with silicone anti-wetting agent such as Surfacil /iL of the purified solution. Repeat extractions (Pierce Chemical Co., Rockford, IL, 61105) until the lead level is reduced to the acceptable according to the manufacturer's instructions. level DO NOT ADD ACID TO THE PURI­ Autosampler cups must be checked for con­ FIED MATRIX MODIFIER SOLUTION. tamination. Lancer (1831 Olive St., St. Louis, NOTE 3. To purify matrix modifier solution, MO, 63103) polystyrene disposable cups have pour the solution into a Teflon or FEP con­ been found to be satisfactory after acid rinsing. tainer. Add 0.25g APDC for each liter of solu­ Alternately, reuseable Teflon or FEP cups may tion. While stirring, adjust the solution to pH be used. 2.9 by dropwise addition of concentrated HNO3 4.3 Argon, standard, welder's grade, com­ (sp gr 1.41). Transfer portions of the solution mercially available. Nitrogen may also be to a separatory funnel, add 100 mL MIBK/liter used if recommended by the instrument of solution, and shake vigorously for at least 5 manufacturer. min. Frequently, vent the funnel in a hood. Col­ lect the extracted solution in the FEP container. 5. Reagents Repeat the extraction with 50 mL MIBK/liter 5.1 Lead standard solution I, 1.00 mL = of solution. Because MIBK can dissolve some 1,000 fig Pb: Dissolve 1.0000 g Pb shot in a min­ plastic autosampler cups, boil the solution for imum of dilute HNO3. Heat to increase rate of at least 10 min in a silicone-treated or acid- dissolution. Add 10 mL high-purity, concen­ rinsed container covered with a watchglass to trated HNO3 (sp gr 1.41) Ultrex or equivalent remove MIBK. and dilute to 1,000 mL with Type 1 water. 5.6 Nitric acid, concentrated, high-purity, 5.2 Lead standard solution II, 1.00 mL = (sp gr 1.41): J. T. Baker "Ultrex" brand HNO3 10.0 fig Pb: Dilute 10.0 mL lead standard solu­ has been found to be adequately pure; however, tion I to 1,000 mL (NOTE 2). each lot must be checked for contamination. NOTE 2. Use acidified Type 1 water Analyze acidified Type 1 water for lead. Add an (paragraph 5.7) to make dilutions. All standards additional 1.5 mL of concentrated HNO3/liter must be stored in sealed Teflon or FEP con­ of water, and repeat analysis. The integrated tainers. Each container must be rinsed twice signal should not increase by more than 0.003 with a small volume of standard before being absorbance-seconds. filled. Standards stored for 6 months in FEP 5.7 Water, acidified, Type 1: Add 1.5 mL containers yielded values equal to those of high-purity, concentrated HNO3 (sp gr 1.41) to freshly prepared standards. each liter of water. 5.3 Lead standard solution III, 1.00 mL = 5.8 Water, Type 1. 1.00 Mg Pb: Dilute 100.0 mL lead standard so­ lution II to 1,000 mL. This standard is used to 6. Procedure prepare working standards serially at time of 6.1 Systematically clean and rinse work analysis. areas with deionized water on a regular 5.4 Lead standard solution IV, 1.00 mL = schedule. Use a laminar flow hood or a "clean 0.010 jig Pb: Dilute 10.0 mL lead standard solu­ room" environment during sample transfers. tion III to 1,000 mL. This standard also is used Ideally, the autosampler and the graphite fur­ to prepare working standards serially at time nace should be in a clean environment. of analysis. 6.2 Soak autosampler cups at least over­ 5.5 Matrix modifier solution, 40 g night in a 1+1 solution of Type 1 water and NH4H2PO4/L: Add 40.0 g NH4H2PO4 to 950 high-purity nitric acid. mL TVpe 1 water, mix, and dilute to 1,000 mL. 6.3 Rinse the sample cups twice with sam­ Analyze 20 /*L of matrix modifier for lead ple before filling. Place cups in sample tray and contamination. If the lead reading is more than cover. Adjust sampler so that only the injection 0.005 absorbance-seconds, purify the solution by tip contacts the sample. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 251

Relative 6.4 In sequence, inject 20-^iL aliquots of standard blank and working standards plus 5 j*L of Number of Mean Standard deviation deviation modifier each and analyze. Analyze the blank replicates (MO/L) bO/L) (percent) 4 0.62 0.17 27 and working standards twice. Construct the 4 1.80 .27 15 analytical curve from the integrated peak areas 4 5.68 .05 .9 10 24.00 .77 3.2 (absorbance-seconds). Generally, the curve 14 48.31 .79 1.6 should be linear to a peak-absorbance (peak- height) value of 0.40 absorbance units. 9.3 The precision and bias for the Zeeman 6.5 Similarly, inject and analyze the samples background correction were tested on deionized twice. Every tenth sample cup should contain water and tap water (specific conductance 280 either a standard or a reference material* /tS/cm). A known amount of lead was added to 6.6 Restandardize as required. Minor each sample, and single-operator precision and changes of values for known samples usually in­ bias for six replicates are as follows: dicate deterioration of the furnace tube, contact Relative rings, and (or) platform. A major variation Amount Amount Standard standard usually indicates either autosampler malfunc­ added found deviation deviation Recovery (percent) (percent) tion or residue buildup from a complex matrix OiQ/L) 0*9/L) (M9/U in a previous sample. Deionized water 11 10.63 0.48 4.5 97 13.5 13.30 .78 5.9 98 7. Calculations 15 15.27 .96 6.3 102 22 21.40 .58 2.7 97 Determine the micrograms per liter of lead in 30 29.37 .54 1.8 98 each sample from the digital display or printer Tap water (NOTE 4) output. Dilute those samples containing concen­ 11 10.15 1.19 10 92 trations of lead that exceed the working range 13.5 15.37 2.40 15 114 15 15.18 .92 5.6 101 of the method; repeat the analysis, and multi­ 22 20.88 .83 3.7 95 ply by the proper dilution factors. 30 30.81 1.70 5.3 103

8. Report NOTE 4. The tap water contained 1.3 jig/L of Report lead, dissolved (01049), concentrations lead, and the standard deviation and percent as follows: less than 10.0 j*g/L, nearest 0.1 /tg/L; relative standard deviation were calculated 10 /xg/L and above, two significant figures for prior to subtraction of lead originally present. both deuterium background correction and 9.4 The precision and bias for the deuterium Zeeman background correction. background method were tested on deionized water and tap water (specific conductance 280 /xS/cm). A known amount of lead was added to 9. Precision each sample, and single-operator precision and 9.1 Analysis of six samples six times each bias for six replicates are as follows: by a single operator using deuterium back­ ground correction is as follows: Relative Amount Amount Standard standard added found deviation deviation Recovery Mean Standard deviation Relative standard deviation (MQ/L) (MO/L) (MO/L) {percent) (percent) WL> 0*fl/D _____(percent)_____ Deionized water 1.13 0.13 12 2.06 .12 5.7 11 10.70 0.81 7.6 97 3.95 .16 4.1 13.5 12.63 1.18 9.3 94 6.02 .22 3.6 15 13.82 .76 5.5 92 22 21.18 .86 4.1 96 10.41 .32 3.1 30 30.60 1.72 5.6 102 20.21 .35 1.7 Tap water (NOTE 4) 11 10.64 .63 5.3 97 13.5 15.37 1.59 9.9 114 9.2 Analysis of five samples by a single 15 17.78 3.70 19.4 119 operator using Zeeman background correction 22 21.49 1.97 8.6 98 is as follows: 30 29.68 1.13 3.7 99 252 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 9.5 Interlaboratory precision for dissolved standards, section 11, water: Philadelphia, v. 11.01, lead for 16 samples within the range of 3.4 to p. 39-41. Cooksey, M., and Baroett, W. B., 1979, Matrix modifica­ 37.4 jig/L, without regard to type of background tion and the method of additions in flameless atomic correction and use of matrix modifiers, if any, absorption: Atomic Absorption Newsletter, v. 18, may be expressed as follows: p. 101-5. Fernandez, F. J., Beatty, M. M., and Barnett, W. B., 1981, Use of the L'vov platform for furnace atomic absorp­ ST = 0.448X + 1,478 tion applications: Atomic Spectroscopy, v. 2, p. 16-21. Hinderberger, E. J., Kaiser, M. L., and Koirtyohann, S. R., where 1981, Furnace atomic absorption analysis of biological ST = overall precision, micrograms per liter, samples using the L'vov platform and matrix modifica­ tion: Atomic Spectroscopy, v. 2, p. 1-11. and Manning, D. C., and Slavin, W.t 1983, The determination X = concentration of lead, micrograms per of trace elements in natural waters using the stabiliz­ liter. ed temperature platform furnace: Applied Spectroscopy, The correlation coefficient is 0.8247. v. 37, p. 1-11. Ottaway, J. M., 1982, A revolutionary development in graphite furnace atomic absorption: Atomic Spec­ troscopy, v. 3, p. 89-92. References Slavin, W., Carnrick, G. R., and Manning, D. C., 1982, Magnesium nitrate as a matrix modifier in the stabilized American Society for Testing and Materials, 1984, Annual temperature platform furnace: Analytical Chemistry, book of American Society for Testing and Materials v. 54, p. 621-4. Lead, atomic emission spectrometric, ICP

Parameter and Code: Lead, dissolved, 1-1472-85 fcig/L as Pb): 01049

2. Summary of method method utilizing an induction-coupled argon Lead is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 253

Lead, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Lead, total, 1-5474-85 (mg/kg as Pb): none assigned

2. Summary of method hotplate at 200 °C. Lead is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec* homogenized. The sample is digested with a trometry. See method 1-5474, metals, major combination of nitric, hydrofluoric, and per­ and minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a spectrometric, direct. 255

Lithium, atomic absorption spectrometric, direct

Parameters and Codes: Lithium, dissolved, 1-1425-85 (pg/L as Li): 01130 Lithium, total recoverable, I-3425-85 fcg/L as Li): 01132 Lithium, suspended recoverable, I-7425-85 fcg/L as Li): 01131 Lithium, recoverable-from-bottom-material, dry wt, I-5425-85 (/tg/g as Li): 01133

1. Application 3. Interferences 1.1 This method may be used to analyze The following elements interfere when the in­ water and water-suspended sediment contain­ dicated concentrations are exceeded: sodium, ing at least 10 /xg/L of lithium. Sample solutions 1,000 mg/L; potassium, 100 mg/L; magnesium, containing more than 1,000 /ig/L need either to 200 mg/L; calcium, 200 mg/L; chloride, 1,000 be diluted or to be read on a less expanded mg/L; sulfate, 2,000 mg/L; nitrate, 100 mg/L; scale. and strontium, 5,000 /tg/L. 1.2 Brines need to be diluted to eliminate in­ terference from other elements. (See section 3, 4. Apparatus "Interferences.") If the lithium concentrations 4.1 Atomic absorption spectrometer, in the diluted samples are below detection, the equipped with electronic digital readout and undiluted samples need to be analyzed by the automatic zero and concentration controls. standard-addition method. 4.2 Refer to the manufacturer's manual to 1.3 Suspended recoverable lithium is optimize instrument for the following: calculated by subtracting dissolved lithium Grating ———————— Visible from total recoverable lithium. 1.4 This method may be used to analyze bot­ Wavelength ————— 670.8 nm Source (hollow-cathode tom material containing at least 1 j*g/g of lith­ lamp) ———————— Lithium ium. Prepared sample solutions containing more Oxidant ———————— Air than 1,000 jtg/L need either to be diluted or to Fuel ————————— Acetylene be read on a less expanded scale. 1.5 Total recoverable lithium in water-sus­ Type of flame ———— Oxidizing pended sediment needs to undergo preliminary 4.3 The 50-mm (2-in.), flathead, single-slot digestion-solubilization by method 1-3485, and burner allows a working range of 10 to 1,000 recoverable lithium in bottom material needs to /*g/L. Different burners may be used according undergo preliminary digestion-solubilization by to manufacturers' instructions. method 1-5485 before being determined. 5. Reagents 2. Summary of method 5.1 Lithium standard solution 7,1.00 mL = 2.1 Lithium is determined by atomic absorp­ 1,000 fig Li: Dissolve 9.936 g LiNO3 in demin- tion spectrometry by direct aspiration of the eralized water and dilute to 1,000 mL. sample solution into an air-acetylene flame 5.2 Lithium standard solution //, 1.00 = (Fishman and Downs, 1966). 10.0 /ig Li: Dilute 10.0 mL lithium standard 2.2 The procedure may be automated by the solution I to 1,000 mL with demineralized addition of a sampler and either a strip-chart water. This solution is used to prepare working recorder or a printer or both. standards at time of analysis. 257 258 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Lithium working standards: Prepare a per gram; 10 jig/g and above, two significant series of at least six working standards contain­ figures. ing from 10 to 1,000 j*g/L of lithium by ap­ propriate dilution of lithium standard solution 9. Precision II. Prepare fresh daily. * 9.1 Precision for dissolved lithium for 19 samples within the range of 32 to 632 j*g/L may 6. Procedure be expressed as follows: Aspirate the blank (demineralized water) to set the automatic zero control. Use the auto­ Sr=0.080X+ 1.13 matic concentration control to set the concen­ trations of standards. Use at least six where standards. Calibrate the instrument each time ST = overall precision, micrograms per liter, a set of samples is analyzed and check calibra­ and tion at reasonable intervals. X = concentration of lithium, micrograms per liter. 7. Calculations The correlation coefficient is 0.8270. 7.1 Determine the micrograms per liter of 9.2 Precision for dissolved lithium for five dissolved or total recoverable lithium in each of the 19 samples expressed in terms of the per­ sample solution from the digital display or cent relative standard deviation is as follows: printer while aspirating each sample. Dilute Number of Relative standard deviation those samples containing lithium concentra­ laboratories _____(percent)_____ tions that exceed working range of the method 13 32 12 and multiply by the proper dilution factors. 10 113 9 7.2 To determine micrograms per liter sus­ 12 215 7 pended recoverable lithium, subtract dissolved- 10 395 4 12 632 lithium concentration from total-recoverable- 7 lithium concentration. 9.3 It is estimated that the percent relative 7.3 To determine micrograms per gram of standard deviation for total recoverable and lithium in bottom-material samples, first deter­ suspended recoverable lithium and for recov­ mine micrograms per liter of lithium as in erable lithium in bottom material will be greater paragraph 7.1; then than that reported for dissolved lithium. 9.4 Precision for total recoverable lithium expressed in terms of percent relative standard /L L. x mL of original digest deviation for one water-suspended sediment is Li (/ig/g) = ______1,000____ as follows: wt of sample (g) Number of Mean Relative standard deviation laboratories WM _____(percent)_____ 8. Report 7 116 17 8.1 Report lithium, dissolved (01130), total- 6 222 recoverable (01132), and suspended-recoverable (01131), concentrations as follows: less than 100 pg/L, nearest 10 /ig/L; 100 jtg/L and above, two Reference significant figures. Fishman, M. J., and Downs, S. C., 1966, Methods for 8.2 Report lithium, recoverable-from- analysis of selected metals in water by atomic absorp­ bottom-material (01133), concentrations as tion: U.S. Geological Survey Water-Supply Paper follows: less than 10 jig/g, nearest microgram 1540-C, p. 30-5. Lithium, atomic emission spectrometric, ICP

Parameter and Code: Lithium, dissolved, 1-1472-85 fciQ/L as Li): 01130

2. Summary of method method utilizing an induction-coupled argon Lithium is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 259

Lithium, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Lithium, total, 1-5474-85 (mg/kg as Li): none assigned

2. Summary of method hotplate at 200 °C. Lithium is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec- homogenized. The sample is digested with a trometry. See method 1-5474, metals, major combination of nitric, hydrofluoric, and per­ and minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a spectrometric, direct. 261

Magnesium, atomic absorption spectrometric, direct

Parameters and Codes: Magnesium, dissolved, 1-1447-85 (mg/L as Mg): 00925 Magnesium, total recoverable, I-3447-85 (mg/L as Mg): none assigned Magnesium, suspended recoverable, 1-7447-85 (mg/L as Mg): 00926 Magnesium, recoverable-from-bottom-material, dry wt, 1-5447-85 (mg/kg as Mg): 00924

1. Application masked by addition of lanthanum. Because low 1.1 This method may be used to analyze at­ magnesium values result if the pH of the sam­ mospheric precipitation, water, brines, and ple is above 7, standards are prepared in hydro­ water-suspended sediment. chloric acid solution and samples are preserved 1.2 Two analytical ranges for magnesium in the field with use of nitric acid solution. are included: from 0.01 to 5*0 mg/L and from 2.5 3.2 Nitrate, sulfate, and silica interfere, but to 50 mg/L. Sample solutions containing mag­ in the presence of lanthanum chloride- nesium concentrations greater than 50 mg/L hydrochloric acid solution at least 2,000 mg/L, need to be diluted. 1,000 mg/L, and 200 mg/L, respectively, can be 1.3 Suspended recoverable magnesium is tolerated. The addition of nitric acid at the time calculated by subtracting dissolved magnesium of collection to preserve the samples causes no from total recoverable magnesium. problem in the following procedure. 1.4 This method may be used to analyze bot­ 3.3 Sodium, potassium, and calcium cause tom material containing at least 10 mg/kg of no interference at concentrations less than 400 magnesium. Prepared sample solutions contain­ mg/L. ing more than 50 mg/L to be diluted. 1.5 Total recoverable magnesium in water- 4 Apparatus suspended sediment needs to undergo prelim­ 4.1 Atomic absorption spectrometer inary digestion-solubilization by method 1-3485, equipped with electronic digital readout and and recoverable magnesium in bottom material automatic zero and concentration controls. needs to undergo preliminary digestion-solubili­ 4.2 Refer to manufacturer's manual to op­ zation by method 1-5485 before being determined. timize instrument for the following: Grating ———————— Ultraviolet 2. Summary of method Wavelength ————— 285.2 nm 2.1 Magnesium is determined by atomic ab­ Source (hollow-cathode sorption spectrometry (Fishman and Downs, lamp) ———————— Magnesium 1966). Lanthanum chloride is added to mask in­ Oxidant ———————— Air terferences. Fuel —————————— Acetylene 2.2 This procedure may be automated by the Type of flame ———— Slightly addition of a sampler, a proportioning pump, reducing and either a strip-chart recorder or a printer or 4.3 The 50-mm (2-in.), flathead, single-slot both (fig. 28). burner allows a working range of 0.01 to 5.0 mg/L. This burner, rotated 90 °, allows a work­ 3. Interferences ing range of 2.5 to 50 mg/L. Different burners 3.1 The interference caused by aluminum may be used according to manufacturers' in­ concentrations greater than 2,000 figlL is structions. 263 264 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

pirator Water Long O.OSlin mixing coil 2.52 mL/min 105056) 1 t O.OSlin Sample 2.52 mL/min 0 Air IN/] O.OSlin Sampler ' \S vj 2.52 mL/min PS- 3 Lanthanum 0.035in chloride 0.42 mL/min ste

» i Water To samplei * -*——— O.OSlin 2.52 mL/min wash rece ptacle

Figure 28.—

5. Reagents 7. Calculations 5.1 Lanthanum chloride solution, 87 g/L: 7.1 Determine the milligrams per liter of Mix 29 g La2O3 with a few milliliters of demin- dissolved or total recoverable magnesium in eralized water to form a slurry. Slowly add 250 each sample solution from the digital display or mL concentrated HC1 (sp gr 1.19) while stirring printer while aspirating each sample. Dilute (reaction may be violent) to dissolve the La2O3. those samples containing magnesium concen­ Dilute to 500 mL with demineralized water. trations that exceed the working range of the 5.2 Magnesium standard solution I, 1.00 method and multiply by the proper dilution mL = 0.50 mg Mg: Dissolve 0.500 g pure factors. metallic Mg in a minimum amount of dilute 7.2 To determine milligrams per liter sus­ HC1, and dilute to 1,000 mL with demineralized pended recoverable magnesium, subtract water. dissolved-magnesium concentration from total- 5.3 Magnesium working standards: Prepare recoverable-magnesium concentration. a series of at least six working standards con­ 7.3 To determine milligrams per kilogram of taining either from 0.01 to 5.0 mg/L or from 2.5 magnesium in bottom-material samples, first to 50 mg/L magnesium by appropriate dilution determine the milligrams per liter of magnesium of magnesium standard solution I. Add 1.0 mL in each sample as in paragraph 7.1; then LaClg solution for each 10 mL of working standard. Similarly, prepare a demineralized mL of original digest water blank. mg/LMgX Mg(mg/kg) = 1000 6. Procedure wt of sample (kg) 6.1 Add 1.0 mL lanthanum chloride solution to 10.0 mL of sample solution. 8. Report 6.2 Aspirate the blank to set the automatic 8.1 Report magnesium, dissolved (00925), zero control. Use the automatic concentration total-recoverable (none assigned), and sus­ control to set the concentrations of standards. pended-recoverable (00926), concentrations as Use at least six standards. Calibrate the instru­ follows: less than 1.0 mg/L, two decimals; 1.0 ment each time a set of samples is analyzed and to 10 mg/L, one decimal; 10 mg/L and above, check calibration at reasonable intervals. two significant figures. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 265 8.2 Report magnesium, recoverable-from- Number of Mean Relative standard deviation laboratories (mg/L) ____(percent)____ bottom-material (00924), concentrations as 20 0.10 50 follows: less than 1,000 mg/kg, nearest 10 23 1.98 9 mg/kg; 1,000 mg/kg and above, two significant 38 11.1 7 40 54.7 7 figures. 39 120 7 9. Precision 9.3 Precision for dissolved magnesium 9.1 Precision for dissolved magnesium for 35 within the range of 0.03 to 5.2 mg/L in terms samples within the range of 0.1 to 120 mg/L of the percent relative standard deviation by a may be expressed as follows: single operator is as follows:

Number of Relative standard deviation laboratories (mg/L) ____(percent)____ ST = 0.062X+0.003 8 0.033 21.2 8 .315 1.6 7 .993 2.6 6 5.18 4.2 where 9.4 It is estimated that the percent relative — overall precision, milligrams per liter, standard deviation for total and suspended and recoverable magnesium and for recoverable X = concentration magnesium, milligrams magnesium in bottom material will be greater per liter. than that reported for dissolved magnesium. The correlation coefficient is 0.9823. 9.2 Precision for dissolved magnesium for Reference five of the 35 samples expressed in terms of the Fishman, M. J., and Downs, SL C, 1966, Methods for analysis percent relative standard deviation is as of selected metals in water by atomic absorption: U.S. follows: Geological Survey Water-Supply Paper 1540-C, p. 30-5.

Magnesium, atomic absorption spectrometric, direct-EPA

Parameter and Code: Magnesium, total recoverable, 1-3448-85 (mg/L as Mg): 00927

1. Application addition of nitric acid to the sample as a preser­ 1.1 This method may be used to analyze vative at the time of collection causes no prob­ water-suspended sediment. lem in the following procedure. Samples should 1.2 For ambient water, analysis may be be evaporated just to dryness following HNO3 made on a measured portion of the acidified digestion to avoid any possible nitrate inter­ water-suspended sediment sample. ference. 1.3 For all other waters, including domestic 3.3 Sodium, potassium, and calcium cause and industrial effluent, the atomic absorption no interference at concentrations less than 400 procedure must be preceded by a digestion- mg/L. solubilization as specified below. In cases where the analyst is uncertain about the type of sam­ 4. Apparatus ple, the digestion-solubilization procedure must 4.1 Atomic absorption spectrometer be used. equipped with electronic digital readout and 1.4 Two analytical ranges are provided: from automatic zero and concentration controls. 0.1 to 10 mg/L of Mg and from 2.5 to 50 mg/L. 4.2 Refer to the manufacturer's manual to Samples containing magnesium at concentra­ optimize instrument for the following: tions greater than 50 mg/L need to be diluted. Grating ———————— Ultraviolet Wavelength ————— 285.2 nm 2. Summary of method Source (hollow-cathode 2.1 Magnesium is determined by atomic ab­ lamp) ———————— Magnesium sorption spectrometry (Fishman and Downs, Oxidant ———————— Air 1966). Lanthanum chloride is added to mask in­ Fuel —————————— Acetylene terferences. Type of flame ———— Slightly 2.2 Effluent samples must undergo a pre­ reducing liminary nitric acid digestion followed by a 4.3 The 50-mm (2-in.), flathead, single-slot hydrochloric acid solubilization. burner allows a working range of 0.1 to 10 mg/L. This burner, rotated 90°, allows a range of 2.5 3. Interferences to 50 mg/L. Different burners may be used ac­ 3.1 The interference caused by aluminum at cording to manufacturers1 instructions. concentrations greater than 2,000 /ig/L is masked by addition of lanthanum. Because low 5. Reagents magnesium values result if the pH of the sam­ 5.1 Hydrochloric acid, GM: Dilute 500 mL ple is above 7, standards are prepared in hydro­ concentrated HC1 (sp gr 1.19) to 1L with demin- chloric acid solution and samples are preserved eralized water. in the field using a nitric acid solution. 5.2 Hydrochloric acid, 0.3M: Dilute 25 mL 3.2 Nitrate, sulfate, and silica interfere, but concentrated HC1 (sp gr 1.19) to 1 L with in the presence of lanthanum chloride-acid solu­ demineralized water. tion at least 2,000 mg/L, 1,000 mg/L, and 200 5.3 Lanthanum chloride solution, 87 g/L: mg/L, respectively, can be tolerated. The Mix 29 g La2O3 with a few milliliters of

267 268 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS demineralized water to form a slurry. Slowly (Whatman No. 41 or equivalent), rinsing the add 250 mL concentrated HC1 (sp gr 1.19) while filter with hot, dilute 0.3M HC1. Dilute to the stirring (reaction may be violent) to dissolve the original volume with demineralized water. La2O3. Dilute to 500 mL with demineralized 6.8 Add 1.0 mL lanthanum chloride solution water. per 10.0 mL of sample. 5.4 Magnesium standard solution 7, 1.00 6.9 Aspirate the blank to set the automatic mL = 0.50 mg Mg: Dissolve 0,500 g pure zero control. Use the automatic concentration metallic Mg in a minimum amount of dilute control to set the concentrations of standards. HC1, and dilute to 1,000 mL with demineralized Use at least six standards. Calibrate the instru­ water* ment each time a set of samples is analyzed and 5.5 Magnesium working standards: Prepare check calibration at reasonable intervals. a series of at least six working standards con­ taining from 0.1 to 50 mg/L magnesium by 7. Calculations diluting magnesium standard solution I. Add Determine the milligrams per liter of 1.0 mL LaCl3 solution for each 10 mL of work­ magnesium in each sample from the digital ing standard. display or printer while aspirating each sample. 5.6 Nitric acid, concentrated (sp gr 1.41). Dilute those samples containing magnesium concentrations that exceed the working range 6. Procedure of the method and multiply by the proper dilu­ 6.1 Transfer the entire sample to a beaker. tion factors. 6.2 Rinse the sample bottle with 3 mL con­ centrated HNO3 for each 100 mL of sample and 8. Report add to the beaker. Prepare a blank using 3 mL Report magnesium, total-recoverable (00927), concentrated HNO3 per 100 mL of demineral­ concentrations as follows: less than 10 mg/L, ized water. one decimal; 10 mg/L and above, two significant 6.3 Evaporate samples and blank to dryness figures. on a hotplate, making sure the samples do not boil. 9. Precision 6.4 Cool and add an additional 3 mL concen­ It is estimated that the percent relative stand­ trated HNO3 to the beaker. Cover with a ard deviation for total recoverable magnesium watchglass, return to the hotplate, and gently over the range of the method will be greater reflux the sample. than 9 percent. 6.5 Continue heating, adding additional acid as necessary, until digestion is complete (in­ References dicated by a light-colored residue). Evaporate just to dryness. Fishman, M. J., and Downs, S. C., 1966, Methods for 6.6 Add 6 mL 6Af HC1 solution per 100 mL analysis of selected metals in water by atomic absorp­ of original sample and warm the beaker to tion: U.S. Geological Survey Water-Supply Paper 1540-C, p. 30-5. dissolve the residue. U.S. Environmental Protection Agency, 1979, Methods for 6.7 Wash the watchglass and beaker with chemical analysis of water and wastes: Cincinnati, demineralized water and filter the sample p. 215.1-1. Magnesium, atomic emission spectrometric, ICP

Parameter and Code: Magnesium, dissolved, 1-1472*85 (mg/L as Mg): 00925

2. Summary of method method utilizing an induction-coupled argon Magnesium is determined simultaneously plasma as an excitation source. See method with several other constituents on a single sam­ 1-1472, metals, atomic emission spectrometric, ple by a direct-reading emission spectrometric ICP. 269

Magnesium, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Magnesium, total, 1-5473-85 (mg/kg as Mg): none assigned Magnesium, total, 1-5474-85 (mg/kg as Mg): none assigned

2. Summary of method spectrometry. See method 1-5473, metals, ma­ 2.1 A sediment sample is dried, ground, jor, total-in-sediment, atomic absorption spec­ and homogenized. The sample is then treated trometric, direct. and analyzed by one of the following 2.1.2 The sample is digested with a combina­ techniques. tion of nitric, hydrofluoric, and perchloric acids 2.1.1 The sample is fused with a mixture of in a Teflon beaker heated on a hotplate at lithium metaborate and lithium tetraborate in 200 °C. Magnesium is determined on the result­ a graphite crucible in a muffle furnace at ing solution by atomic absorption spectrometry. 1000 °C. The resulting bead is dissolved in See method 1-5474, metals, major and minor, acidified, boiling, demineralized water and total-in-sediment, atomic absorption spec­ magnesium determined by atomic absorption trometric, direct. 271

Manganese, atomic absorption spectrometric, cheiation-extraction

Parameter and Code: Manganese, dissolved, 1-1456-85 0*g/L as Mn): 01056

1. Application 5. Reagents This method may be used to analyze water 5.1 Ammonium pyrrolidine dithiocarbamate and brines containing from 1 to 100 ^g/L of man­ solution, 4 g/100 mL: Dissolve 4 g APDC in ganese. Brines containing more than 100 /xg/L demineralized water and dilute to 100 mL. need either to be diluted or to be read on a less Prepare fresh daily. expanded scale. Samples containing more than 5.2 Bromocresol green indicator solution, 0.1 100 /ig/L need either to be diluted prior to g/100 mL: Dissolve 0.1 g bromocresol green in chelation-extraction or to be analyzed by the 100 mL 20-percent ethanol. atomic absorption spectrometric direct method, 5.3 Chloroform. providing that the interference limits discussed 5.4 Hydrochloric acid, 4M: Mix 333 mL con­ in that method are not exceeded. centrated HC1 (sp gr 1.19) with demineralized water and dilute to 1 L. 2. Summary of method 5.5 Manganese standard solution I, 1.00 Manganese is determined by atomic absorption mL = 100 jig Mn: Dissolve 0.1000 g manganese spectrometry following chelation with ammonium flakes in a minimum of dilute HNO3. Heat to pyrrolidine dithiocarbamate (APDC) and extrac­ increase rate of dissolution. Add 10.0 mL of con­ tion with chloroform. The extract is evaporated centrated HNO3 (sp gr 1.41) and dilute to 1,000 to dryness, treated with hot nitric acid to destroy mL with demineralized water. organic matter, dissolved in hydrochloric acid, and 5.6 Manganese standard solution II, 1.00 diluted to a specified volume with demineralized mL = 1.00 ^g Mn: Immediately before use, water. The resulting solution is aspirated into the dilute 10.0 manganese standard solution I to air-acetylene flame of the spectrometer. 1,000 mL with demineralized water. This solu­ 3. Interferences tion is used to prepare working standards at Concentrations of iron to 4 X 106 jig/L do not time of analysis. interfere; higher concentrations were not tested. 5.7 Sodium hydroxide, 0.25M: Dissolve 10 g NaOH in demineralized water and dilute to 1 L. 4. Apparatus 4.1 Atomic absorption spectrometer 6. Procedure equipped with electronic digital readout and 6.1 Clean all glassware used in this deter­ automatic zero and concentration controls. mination with warm, dilute HNO3 (1+9) and 4.2 Refer to the manufacturer's manual to rinse with demineralized water immediately optimize instrument for the following: before use. Grating ———————— Ultraviolet 6.2 Pipet a volume of sample containing less Wavelength ————— 279.5 nm than 5 /ig Mn (50 mL max) into a 125-mL Source (hollow-cathode separatory funnel Adjust the volume to approx lamp) ———————— Manganese 50 mL. Oxidant ———————— Air 6.3 Prepare a blank and at least six stand­ Fuel —————————— Acetylene ards, and adjust the volume of each to approx Type of flame ———— Oxidizing 50 mL with demineralized water. 273 274 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6.4 Add 2 drops bromocresol green indicator standards use the automatic concentration con­ solution and adjust the pH of each sample, trol to set the digital display to read concentra­ standard, and blank to 4.0 (light olive-green col­ tions of standards. Use at least six standards. or) with the addition of 0.25M NaOH. Calibrate the instrument each time a set of 6.5 Add 5.0 mL APDC solution and mix. samples is analyzed and check calibration at 6.6 Add 10 mL chloroform and shake for 2 reasonable intervals. min. 6.7 Allow the phases to separate and drain 7. Calculations the chloroform phase into a 100-mL beaker. Determine the micrograms per liter of dis­ 6.8 Repeat the extraction with an additional solved manganese in each sample from the 10 mL chloroform and drain the chloroform digital display or printer while aspirating each phase into the same beaker. sample. Dilute those samples containing con­ 6.9 Place the beaker on a steam bath and centrations of manganese that exceed the work­ evaporate just to dryness. ing range of the method. Repeat those analyses 6.10 Hold the beaker at a 45° angle, and slowly and multiply by the proper dilution factors. add 2 mL concentrated HNO3 (sp gr 1.41), rotat­ ing the beaker to effect thorough contact of the 8. Report acid with the residue (CAUTION—NOTE 1). Report manganese, dissolved (01056), concen­ NOTE 1. If acid is added to the beaker in a trations as follows: less than 10 ^g/L, nearest vertical position, a violent reaction may occur microgram per liter; 10 jtg/L and above, two accompanied by high heat and spattering. significant figures. 6.11 Place the beaker on a hotplate at low heat and evaporate just to dryness. 9. Precision 6.12 Add 2 mL 4M HC1 and heat, while swirl­ Precision for dissolved manganese for three ing, for 1 min. samples expressed in terms of percent relative 6.13 Cool and transfer the solution to a 10-mL standard deviation is as follows: volumetric flask and dilute to volume with Number of Mean Relative standard deviation demineralized water. laboratories _____(percent)_____ 6.14 While aspirating the blank use the 6 22.2 16 automatic zero control to set the digital display 6 121 7 to read zero concentration. While aspirating 291 5 Manganese, atomic absorption spectrometric, direct

Parameters and Codes: Manganese, dissolved, 1-1454-85 G*g/L as Mn): 01056 Manganese, total recoverable, I-3454-85 (pg/L as Mn): 01055 Manganese, suspended recoverable, I-7454-85 (/ig/L as Mn): 01054 Manganese, recoverable-from-bottom-material, dry wt, I-5454-85 (jig/g as Mn): 01053

1. Application 3. Interferences 1.1 This method may be used to analyze Magnesium (100 mg/L) and silica (100 mg/L) water and water-suspended sediment contain­ do not interfere. Magnesium in excess of 100 ing at least 10 /*g/L of manganese. Sample solu­ mg/L may present some interference, especially tions containing more than 1,000 /*g/L need when the manganese concentration exceeds either to be diluted or to be read on a less ex­ 500 ptg/L. Silica interferes above 100 mg/L. Iron panded scale. Brines need to be analyzed by the concentration to 4 X 106 j*g/L does not atomic absorption spectrometric, chelation- interfere. extraction method, providing that the inter­ ferences discussed in that method are not 4. Apparatus exceeded. 4.1 Atomic absorption spectrometer 1.2 Suspended recoverable manganese is equipped with electronic digital readout and calculated by subtracting dissolved manganese automatic zero and concentration controls. from total recoverable manganese. 4.2 Refer to the manufacturer's manual to 1.3 This method may be used to analyze bot­ optimize instrument for the following: tom material containing at least 1 ptg/g of Grating ——————— Ultraviolet manganese. Prepared sample solutions con­ Wavelength ————'— 279.5 nm taining more than 1,000 /tg/L need either to Source (hollow-cathode be diluted or to be read on a less expanded lamp) ——————— Manganese scale. Oxidant ——————— Air 1.4 Total recoverable manganese in water- Fuel —————————— Acetylene suspended sediment needs to undergo Type of flame ————— Oxidizing preliminary digestion-solubilization by method 4.3 The 100-mm (4-in.), flathead, single-slot 1-3485, and recoverable manganese in bottom burner allows a working range from 10 to 1,000 material needs to undergo preliminary diges­ /ig/L. Different burners may be used according tion-solubilization by method 1-5485 before be­ to manufacturers' instructions. ing determined. 5. Reagents 2. Summary of method 5.1 Manganese standard solution /, 1.00 2.1 Manganese is determined by atomic ab­ mL = 100 /ig Mn: Dissolve 0.1000 g manganese sorption spectrometry by direct aspiration of flakes in a minimum of dilute HNO3. Heat to the sample into an air-acetylene flame without increase rate of dissolution. Add 10.0 mL of con­ preconcentration or pretreatment. centrated HNO3 (sp gr 1.41) and dilute to 1,000 2.2 The procedure may be automated by the mL with demineralized water. addition of a sampler and either a strip-chart 5.2 Manganese standard solution II, 1.00 recorder or a printer or both. mL = 10.0 fig Mn: Immediately before use, 275 276 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS dilute 10.0 mL manganese standard solution I 8.2 Report manganese, recoverable-from- to 100 *"T, with demineralized water. bottom-material (01053), concentrations as 5.3 Manganese working standards: Prepare follows: less than 10 jig/g, nearest microgram at least six working standards containing from per gram; 10 pg/g and above, two significant 10 to 1,000 jig/L manganese by appropriate dilu­ figures. tion of manganese standard solution II with acidified water. Prepare fresh daily. 9. Precision 5.4 Water, acidified: Add 1.5 mL concen­ 9.1 Precision for dissolved manganese for 30 trated HNO3 (sp gr 1.41) to 1 L of demineral­ samples within the range of 3.0 to 568 /ig/L may ized water. be expressed as follows:

6. Procedure Aspirate the blank (acidified water) to set the ST = 0.056X + 8.28 automatic zero control. Use the automatic con­ centration control to set the concentrations of where standards. Use at least six standards. Calibrate ST = overall precision, micrograms per liter, the instrument each time a set of samples is and analyzed and check calibration at reasonable ^^concentration of manganese, micrograms intervals. per liter. The correlation coefficient is 0.9003. 7. Calculations 9.2 Precision for dissolved manganese for 7.1 Determine the micrograms per liter of six of the 30 samples expressed in terms of dissolved or total recoverable manganese in the percent relative standard deviation is as each sample from the digital display or printer follows: while aspirating each sample. Dilute those samples containing manganese concentrations Number of Mean Relative standard deviation that exceed the working range of the method laboratories fro/L) ____(percent)____ and multiply by the proper dilution factors. 6 3.0 267 6 12 83 7.2 To determine micrograms per liter of 27 60 17 suspended recoverable manganese, subtract 25 106 12 dissolved-manganese concentration from total- 34 256 9 recoverable-manganese concentration. 36 568 7 7.3 To determine micrograms per gram of manganese in bottom-material samples, first 9.3 It is estimated that the percent relative determine the micrograms per liter of standard deviation for total recoverable and manganese as in paragraph 7.1; then suspended recoverable manganese and for recoverable manganese in bottom material will mL of original digest be greater than that reported for dissolved MnX _____1.000____ manganese. Mn (jig/g) 9.4 Precision for total recoverable manga­ wt of sample (g) nese expressed in terms of percent relative standard deviation for two water-suspended 8. Report sediment samples is as follows: 8.1 Report manganese, dissolved (01056), total-recoverable (01055), and suspended- Number of Mean Relative standard deviation recoverable (01054), concentrations as follows: laboratories (Mfl/U _____(percent)____ less than 100 j*g/L, nearest 10 pg/L; 100 jig/L 21 52 44 and above, two significant figures. 22 317 6 Manganese, atomic absorption spectrometric, graphite furnace

Parameter and Code: Manganese, dissolved, 1-1455-85 (/*g/L as Mn): 01056

1. Application quite low. In addition, the use of the graphite 1.1 This method may be used to determine platform reduces the effects of many in­ manganese in low ionic-strength water and terferences. Calcium (60 mg/L), magnesium (14 precipitation. With deuterium background cor­ mg/L)t sodium (56 mg/L), sulfate (110 mg/L), and rection and a 20-/tL sample, the method is ap­ chloride (45 mg/L) do not interfere. Higher con­ plicable in the range from 0.2 to 12 pg/L. With centrations of these constituents were not Zeeman background correction and a 20-/*L investigated. sample, the method is applicable in the range 3.2 Precipitation samples usually contain from 0.2 to 20 pg/L. Sample solutions that con­ very low concentrations of manganese. Special tain manganese concentrations exceeding the precautionary measures must be employed dur­ upper limits must be diluted or preferably be ing both sample collection and laboratory deter­ analyzed by the atomic absorption spec­ mination to prevent contamination. trometric direct or chelation-extraction method, or by the atomic emission spectrometric ICP 4. Apparatus method. 4.1 Atomic absorption spectrometer, for use 1.2 The analytical range and detection limits at 279.5 nm and equipped with background cor­ can be increased or possibly decreased by vary­ rection, digital integrator to quantitate peak ing the volume of sample injected or the in­ areas, graphite furnace with temperature pro­ strumental settings. Purification of reagents grammer, and automatic sample injector. The and use of ASTM Type 1 water (Method programmer must have high-temperature ramp­ D-1193, American Society for Testing and ing and stopped-flow capabilities. Materials, 1984) may result in lower detection 4.1.1 Refer to the manufacturer's manual to limits. optimize instrumental performance. The analytical ranges reported in paragraph 1.1 are 2. Summary of method for a 20-/*L sample with 5 jdL of matrix modifier Manganese is determined by atomic absorp­ (NOTE 1). tion spectrometry in conjunction with a NOTE 1. A 20-pL sample generally requires 30 graphite furnace containing a graphite platform s to dry. Samples that have a complex matrix (Hinderberger and others, 1981). A sample is may require a longer drying and charring time. placed on the graphite platform and a matrix 4.1.2 Graphite furnace, capable of reaching modifier is added. The sample is then evapo­ temperatures sufficient to atomize the element rated to dryness, charred, and atomized using of interest. Warning: dial settings frequently high-temperature ramping. The absorption sig­ are inaccurate and newly conditioned furnaces nal generated during atomization is recorded require temperature calibration. and compared with standards. 4.1.3 Graphite tubes and platforms. Pyrolytically coated graphite tubes and solid 3. Interferences pyrolytic graphite platforms are recommended. 3.1 Interferences in low ionic-strength 4.2 Labware. Many trace metals at very low samples, such as precipitation, normally are concentrations have been found to sorb very 277 278 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS rapidly to glassware. To preclude this, fluori- standard also is used to prepare working stand­ nated ethylene propylene (FEP) or Teflon lab- ards serially at time of analysis. ware may be used. Alternately, glassware, 5.6 Nitric acid, concentrated, high-purity, particularly flasks and pipets, may be treated (sp gr 1.41): J. T. Baker "Ultrex" brand HNO3 with silicone anti-wetting agent such as Surfacil has been found to be adequately pure; however, (Pierce Chemical Co., Rockford, IL, 61105) ac­ each lot must be checked for contamination. cording to the manufacturer's instructions. Analyze acidified Type 1 water for manganese. Autosampler cups must be checked for con­ Add an additional 1.5 mL of concentrated tamination. Lancer (1831 Olive St., St. Louis, HNO3/liter of water, and repeat analysis. The MO, 63103) polystyrene disposable cups have integrated signal should not increase by more been found to be satisfactory after acid rinsing. than 0.001 absorbance-seconds. Alternately, reuseable Teflon or FEP cups may 5.7 Water, acidified, Type 1: Add 1.5 mL be used. high-purity, concentrated HNO3 (sp gr 1.41) to 4.3 Argon, standard, welder's grade, com­ each liter of water. mercially available. Nitrogen may also be 5.8 Water, Type 1. used if recommended by the instrument manufacturer. 6. Procedure 6.1 Systematically clean and rinse work 5. Reagents areas with deionized water on a regular 5.1 Matrix modifier solution, 10 g schedule. Use a laminar flow hood or a "dean Mg(NO3)2/L, Suprapur MCB reagent or room" environment during sample transfers. equivalent: Add 16.8 g Mg(NO3)2-6H2O to 950 Ideally, the autosampler and the graphite fur­ mL Type 1 water, mix, and dilute to 1,000 mL. nace should be in a clean environment. DO NOT ADD ACID TO THE MATRIX 6.2 Soak autosampler cups at least over­ MODIFIER SOLUTION. night in a 1+1 solution of Type 1 water and 5.2 Manganese standard solution I, 1.00 high-purity nitric acid. mL = 1,000 Mg Mn: Dissolve 1.0000 g Mn flakes 6.3 Rinse the sample cups twice with sam­ in a minimum of dilute HNO3. Heat to increase ple before filling. Place cups in sample tray and rate of dissolution. Add 10 mL high-purity, con­ cover. Adjust sampler so that only the injection centrated HNO3 (sp gr 1.41), Ultrex or tip contacts the sample. equivalent, and dilute to 1,000 mL with Type 6.4 In sequence, inject 20-/*L aliquots of 1 water. blank and working standards plus 5 jiL of 5.3 Manganese standard solution II, 1.00 modifier each and analyze. Analyze the blank mL = 10.0 /ig Mn: Dilute 10.0 mL manganese and working standards twice. Construct the standard solution I to 1,000 mL (NOTE 2). analytical curve from the integrated peak areas NOTE 2. Use acidified Type 1 water (para­ (absorbance-seconds). Generally, the curve graph 5.7) to make dilutions. All standards should be linear to a peak-absorbance (peak- must be stored in sealed Teflon or FEP con­ height) value of 0.40 absorbance units. tainers. Each container must be rinsed twice 6.5 Similarly, inject and analyze the samples with a small volume of standard before being twice. Every tenth sample cup should contain filled. Standards stored for 6 months in FEP either a standard or a reference material. containers yielded values equal to those of 6.6 Restandardize as required. Minor changes freshly prepared standards. of values for known samples usually indicate deter­ 5.4 Manganese standard solution HI, 1.00 ioration of the furnace tube, contact rings, andfor mL = 1.00 ^g Mn: Dilute 100.0 mL manganese platform. A major variation usually indicates standard solution II to 1,000 mL. This stand­ either autosampler malfunction or residue buildup ard is used to prepare working standards serial­ from a complex matrix in a previous sample ly at time of analysis. 5.5 Manganese standard solution IV, 1.00 7. Calculations mL = 0.01 fig Mn: Dilute 10.0 mL manga­ Determine the micrograms per liter of nese standard solution III to 1,000 mL. This manganese in each sample from the digital METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 279 display or printer output. Dilute those samples NOTE 3. The tap water contained approx 14.4 containing concentrations of manganese that ex­ /xg/L of manganese, and the standard deviation ceed the working range of the method; repeat the and percent relative standard deviation were analysis, and multiply by the proper dilution calculated prior to subtraction of manganese factors. originally present. 9.4 The precision and bias for the deuterium 8. Report background method were tested on deionized Report manganese, dissolved (01056), concen­ water and tap water (specific conductance 280 trations as follows: less than 10.0 jig/L» nearest /iS/cm). A known amount of manganese was 0.1 /*g/L; 10 ftg/L and above, two significant added to each sample, and single-operator preci­ figures for both deuterium background correc­ sion and bias for six replicates are as follows: tion and Zeeman background correction.

9. Precision Relative Amount Amount Standard standard 9.1 Analysis of four rainwater samples six added found deviation deviation Recovery times each by a single operator using deuterium (MO/L) (pg/L) G*g/L) (percent) (percent) background correction is as follows: Deionized water

Mean Standard deviation Relative standard deviation 3.95 3.89 0.23 5.9 98 (Mg/L) (ftg/L) (percent) 7.9 8.12 .57 7.0 103 13 13.32 .58 4.4 102 0.53 0.07 13.7 15.5 14.76 1.17 7.9 95 1.14 .05 4.8 26 26.12 .72 2.8 100 1.53 .04 2.8 1.79 .05 3.0 Tap water (NOTE 3) 9.2 Analysis of four samples by a single 3.95 6.61 2.19 10.3 167 operator using Zeeman background correction 7.9 9.07 1.43 6.1 115 13 12.16 1.99 7.4 94 is as follows: 15.5 17.53 1.34 5.4 113 Relative 26 23.85 3.07 8.0 92 standard Number of Mean Standard deviation deviation replicates 0*g/L) {^g/L) (percent) 9.5 Intel-laboratory precision for dissolved 7 3.94 0.38 9.6 11 9.92 .60 6.0 manganese for 9 samples within the range of 40 4 15.48 .25 1.6 to 547 j*g/L, without regard to type of back­ 12 19.06 .51 2.7 ground correction and use of matrix modifiers, if any, may be expressed as follows: 9.3 The precision and bias for the Zeeman background correction were tested on deionized ST = 0.144X+5.023 water and tap water (specific conductance 280 ftS/cm). A known amount of manganese was added to each sample, and single-operator preci­ where sion and bias for six replicates are as follows: ST = overall precision, micrograms per liter, and Amount Amount Standard Relative standard X = concentration of manganese, micro- added found deviation deviation Recovery grams per liter. (MO/L) fcio/L) (Mfl/L) (percent) (percent) The correlation coefficient is 0.8074. Deionized water 3.95 4.38 0.35 8.0 111 7.9 8.13 .77 9.5 103 13 13.43 .64 4.8 103 References 15.5 16.03 .77 4.8 103 26 25.45 1.29 5.1 98 American Society for Testing and Materials, 1984, Annual Tap water (NOTE 3) book of A8TM standards, section 11, water: Phila­ 3.95 3.11 1.11 6.4 79 delphia, v. 11.01, p. 39-41. 7.9 6.63 .66 3.2 84 Cooksey, M., and Barnett, W. B., 1979, Matrix modifica­ 13 9.67 1.48 6.2 74 tion and the method of additions in flameless atomic 15.5 14.83 1.59 7.2 96 26 24.94 2.11 5.4 96 absorption: Atomic Absorption Newsletter, v. 18, n. 101-5. 280 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Fernandez, F. J., Beatty, M. M., and Barnett, W. B., 1981, temperature platform furnace: Applied Spectroscopy, Use of the L'vov platform for furnace atomic absorp­ v. 37, p. Ml. tion applications: Atomic Spectroscopy, v. 2, p. 16-21. Ottaway, J. M., 1982, A revolutionary development in Hinderberger, E. J.( Kaiser, M. L., and Koirtyohann, S. R., graphite furnace atomic absorption: Atomic Spec­ 1981, Furnace atomic absorption analysis of biological troscopy, v. 3, p. 89-92. samples using the L'vov platform and matrix modifica­ Slavin, W., Carnrick, G. R., and Manning, D. C., 1982, tion: Atomic Spectroscopy, v. 2, p. 1-11. Magnesium nitrate as a matrix modifier in the stabil­ Manning, D. C., and Slavin, W., 1983, The determination ized temperature platform furnace: Analytical Chemi­ of trace elements in natural waters using the stabilized stry, v. 54, p. 621-4. Manganese, atomic emission spectrometric, ICP

Parameter and Code: Manganese, dissolved, 1-1472-85 (/ig/L as Mn): 01056

2. Summary of method method utilizing an induction-coupled argon Manganese is determined simultaneously plasma as an excitation source. See method with several other constituents on a single sam­ 1-1472, metals, atomic emission spectrometric, ple by a direct-reading emission spectrometric ICP. 281

Manganese, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Manganese, total, 1-5473-85 (mg/kg as Mn): none assigned Manganese, total, 1-5474-85 (mg/kg as Mn): none assigned

2. Summary of method spectrometry. See method 1-5473, metals, ma­ 2.1 A sediment sample is dried, ground, jor, total-in-sediment, atomic absorption spec­ and homogenized. The sample is then treated trometric, direct. and analyzed by one of the following 2.1.2 The sample is digested with a combina­ techniques. tion of nitric, hydrofluoric, and perchloric acids 2.1.1 The sample is fused with a mixture of in a Teflon beaker heated on a hotplate at lithium inelaborate and lithium tetraborate in 200 °C. Manganese is determined on the result­ a graphite crucible in a muffle furnace at ing solution by atomic absorption spectrometry. 1000 °C. The resulting bead is dissolved in See method I- 5474, metals, major and minor, acidified, boiling, demineralized water; manga­ total-in-sediment, atomic absorption spectro­ nese is then determined by atomic absorption metric, direct. 283

Mercury, atomic absorption spectrometric, flameless

Parameters and Codes: Mercury, dissolved, 1-1462-85 fcig/L as Hg): 71890 Mercury, total recoverable, I-3462-85 (pg/L as Hg): 71900 Mercury, suspended recoverable, 1-7462-85 (pg/L as Hg): 71895 Mercury, recoverable-from-bottom-material, dry wt, I-5462-85 (j*g/g as Hg): 71921

1. Application 2.2 This method is based on a procedure 1.1 This method may be used to analyze water described by Hatch and Ott (1968) and is similar and water-suspended sediment containing at in substance to the flameless atomic absorption least 0.5 /tg/L of mercury. Samples containing method in "Methods for Chemical Analysis of mercury concentrations greater than 10 /ig/L Water and Wastes/' published by the Water need to be diluted. Industrial and sewage ef­ Quality Office of the Environmental Protection fluent may be analyzed, as well as samples of Agency (1979). fresh and saline water. 1.2 Suspended recoverable mercury is 3. Interferences calculated by subtracting dissolved mercury 3.1 Some samples may contain volatile from total recoverable mercury. organic compounds that absorb radiation at 1.3 This method may be used to analyze bot­ 253.7 nm and that may be swept from the tom material containing at least 0.01 /ig/g of solution along with the mercury vapor. These mercury. Usually, a 5-g sample of prepared constitute a positive interference, and the pos­ material (method P-0520) is taken for analysis. sibility of their presence must not be over­ For samples containing more than 1.0 pig/g, use looked. less sediment. 3.2 Selenium concentrations, either as selen- 1.4 Total recoverable mercury in water- ate or selenite, up to 10,000 /xg/L do not in­ suspended sediment may be determined after terfere; higher concentrations were not tested. each sample has been thoroughly mixed by vigorous shaking and a suitable sample por­ 4. Apparatus tion has been rapidly withdrawn from the 4.1 Absorption cell (fig. 29). Mount and align mixture. an absorption cell (10- to 20-cm path length) in the light path of the spectrometer. Position a 2. Summary of method 60-watt lamp over the cell (10 to 15 cm) to pre­ 2.1 The cold-vapor, flameless, atomic ab­ vent condensation of water vapor. Attach a suf­ sorption procedure is based on the absorption ficient length of tubing to the outlet of the cell of radiation at 253.7 nm by mercury vapor. and vent to a hood. Connect the inlet of the cell Organic mercury compounds, if present, are to the aerator with a minimum length of plastic decomposed by hot (95 °C) digestion with tubing. Attach a water aspirator to the outlet potassium permanganate and potassium per- of the stopcock (NOTE 1). Alternately, a forced- sulfate in acid solution. The mercuric ions are air pump may be used. then reduced to the elemental state with stan- NOTE 1. The stopcock must remain closed dur­ nous chloride, and the mercury vapor is subse­ ing analysis and be opened only briefly between quently removed from solution by aeration and samples to remove residual mercury vapor from passed through a cell positioned in the light the absorption cell. path of an atomic absorption spectrometer. 4.2 Aerator (fig. 29). 285 286 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Air

Outlet (vent to hood) (PTl

Aerator

300-mL BOD bottle Quartz Quartz window window (25-mm OD )

Figure 29.—Absorption cell and aerator

4.3 Atomic absorption spectrometer and NOTE 2. A larger volume of this reagent can recorder or a commerical mercury analyzer. be prepared if it is kept refrigerated. 4.4 Refer to the manufacturer's manual to 5.2 Mercury standard solution /, 1.00 mL = optimize instrument for the following: 100 /ig Hg: Dissolve 0.1712 g Hg(NO3)2'H2O in Grating ...... Ultraviolet demineralized water. Add 1.5 mL concentrated Wavelength .. 253.7 nm HNO3 and dilute to 1,000 mL with demineral­ Source ...... Mercury-vapor dis­ ized water. charge, hollow- 5.3 Mercury standard solution II, 1.00 cathode, or electrode- mL = 1.00 /ig Hg: Dilute 5.00 mL mercury less-discharge lamp standard solution I and 1.5 mL concentrated 4.5 BOD bottle, 300-mL capacity. HNO3 to 500 mL with demineralized water. 4.6 Water bath or controlled-temperature This and the following mercury standard solu­ oven, 95 °C. tions must be prepared fresh daily. 5.4 Mercury standard solution ///, 1.00 5. Reagents mL = 0.050 fig Hg: Dilute 10.0 mL mercury 5.1 Hydroxylamine hydrochloride-sodium standard solution II and 1.5 mL concentrated chloride solution: Dissolve 10 g NH2OH-HC1 HNO3 to 200 mL with demineralized water. and 12 g NaCl in demineralized water and dilute Use this solution to prepare working standards to 100 mL (NOTE 2). Prepare fresh daily. Alter­ at the time of analysis. natively, 12 g hydroxylamine sulfate may be 5.5 Nitric acid, concentrated (sp gr 1.41), used instead of the hydroxylamine hydro- with low mercury content: duPont, reagent- chloride. grade acid has been found satisfactory. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 287 5.6 Potassium permanganate solution, 50 6.3.3 Add 5 mL concentrated H2SO4 and 2.5 g/L: Dissolve 5 g KMnO4 in demineralized mL concentrated HNO3, mixing after each ad­ water and dilute to 100 mL. Prepare fresh week­ dition. ly. Store in brown glass bottle. 6.3.4 Add 15 mL KMnO4 solution and shake. 5.7 Potassium persulfate solution, 50 g/L: Add additional small amounts of KMnO4 solu­ Dissolve 5 g K2S2O8 in demineralized water tion, if necessary, until the purple color persists and dilute to 100 mL. for at least 15 min. 5.8 Stannous chloride solution, 74 g/L: Add 6.3.5 Add 8 mL K2S2O8 solution, mix, and 22 g SnCl2-2H2O to 250 mL 0.25M H2SO4. This heat for 2 h in a boiling-water bath or for 3 h solution is unstable. Prepare fresh daily. in an oven at 95 °C. Proceed to paragraph 6.5. 5.9 Sulfuric acid, concentrated (sp gr 1.84). 6.4 Follow instructions in paragraphs 6.4.1 5.10 Sulfuric acid, 0.25M: Cautiously add 14 through 6.4.5 for recoverable mercury from bot­ mL concentrated H2SO4 (sp gr 1.84) to tom material. demineralized water and dilute to 1 L. 6.4.1 Place a weighed portion of sample con­ taining less than 1.0 /ig Hg (5 g max) into a 6. Procedure 300-mL capacity BOD bottle and add approx 6.1 Immediately before each use, clean all 100 mL demineralized water. glassware used in this determination by rinsing, 6.4.2 Prepare a blank of demineralized water first with warm, dilute HNO3 (1+4), and then and sufficient standards, and adjust the volume with demineralized water. of each to approx 100 mL with demineralized 6.2 Follow instructions in paragraphs 6.2.1 water. through 6.2.5 for dissolved mercury. 6.4.3 Add 5 mL concentrated H2SO4 and 2.5 6.2.1 Pipet a volume of sample containing less mL concentrated HNO3, mixing after each ad­ than 1.0 A*g Hg (100 mL max) into a 300-mL dition. capacity BOD bottle and adjust the volume to 6.4.4 Add 15 mL KMnO4 solution and shake. approx 100 mL. Add additional small amounts of KMnO4 solu­ 6.2.2 Prepare a blank of demineralized water tion, if necessary, until the purple color persists and sufficient standards, and adjust the volume for at least 15 min. of each to approx 100 mL with demineralized 6.4.5 Add 8 mL K2S2O8 solution, mix, and water. heat for 2 h in a boiling-water bath or for 6.2.3 Add 5 mL concentrated H2SO4 and 2.5 3 h in an oven at 95 °C. Proceed to paragraph mL concentrated HNO3, mixing after each ad­ 6.5. dition. 6.5 Remove from water bath, cool, and add 6.2.4 Add 5 mL KMnO4 solution and shake. NH2OH-HCl-NaCl solution in 2-mL increments Add additional small amounts of KMnO4 solu­ to reduce the excess permanganate, as evi­ tion, if necessary, until the purple color persists denced by the disappearance of the perman­ for at least 15 min. ganate color. 6.2.5 Add 2 mL K2S2O8 solution, mix, and 6.6 Add 5 mL SnCl2 solution to one sample heat for 2 h in a boiling-water bath or for 3 h and immediately attach the bottle to the aerator in an oven at 95 °C. Proceed to paragraph 6.5. (NOTE 3). Record the maximum absorbance. 6.3 Follow instructions in paragraph 6.3.1 After maximum absorbance has been recorded, through 6.3.5 for total recoverable mercury. remove the BOD bottle and open the stopcock 6.3.1 Pipet a volume of well-mixed sample con­ to the vacuum. Momentarily pinch off the vent taining less than 1.0 pig Hg (100 mL max) into tube in order to remove residual mercury vapor a 300-mL capacity BOD bottle and adjust the from the absorption cell. Treat each succeeding volume to approx 100 mL. sample, blank, and standard in a like manner. 6.3.2 Prepare a blank of demineralized water NOTE 3. Use the atomic absorption com­ and sufficient standards, and adjust the volume pressed-air supply or a peristaltic pump to of each to approx 100 mL with demineralized aerate the sample. Adjust the rate of air flow water. to approx 2 L/min. 288 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 7. Calculations where 7.1 Determine the micrograms of mercury in ST = overall precision, micrograms per liter, the sample from a plot of absorbances of stand­ and ards. Exact reproducibility is not obtained, and X = concentration of mercury, micrograms an analytical curve must be prepared with each per liter. set of samples. The correlation coefficient is 0.9229. 7.2 Determine the concentration of dis­ 9.2 Precision for dissolved mercury for six solved or total recoverable mercury in each sam­ of the 23 samples expressed in terms of the per­ ple as follows: cent relative standard deviation is as follows:

1,000 Number of Mean Relative standard deviation Hg (Mg/L) = ^g Hg X laboratories ML) ______(percent)_____ mL sample aliquot 22 0.33 50 15 .60 46 27 1.69 32 7.3 To determine the concentration of sus­ 7 3.46 30 7 6.54 18 pended recoverable mercury, subtract dis- 26 15.5 16 solved-mercury concentration from total-recov­ erable-mercury concentration. 9.3 It is estimated that the percent relative 7.4 Determine the concentration of mercury standard deviation for total recoverable and in air-dried bottom material as follows: suspended recoverable mercury and for recoverable mercury in bottom material will be greater than that reported for dissolved Hg in sample mercury. wt of sample (g) 9.4 Precision for total recoverable mercury expressed in terms of percent relative standard deviation for two water-suspended sediment 8. Report samples is as follows: 8.1 Report mercury, dissolved (71890), total- recoverable (71900), and suspended- recoverable Number of Mean Relative standard deviation (71895), concentrations as follows: less than 10 laboratories (pfl/U _____(percent)_____ /ig/L and greater than or equal to 0.5 pig/L, 19 9.2 32 nearest 0.1 /ig/L; 10 /*g/L and above, two signifi­ 18 11.4 38 cant figures. 8.2 Report mercury, recoverable-from- References bottom-material (71921), concentrations as follows: less than 1.00 ftg/g, nearest 0.01 /*g/g; Fishman, M. J., and Brown, Eugene, 1976, Selected methods 1-0 /ig/g and above, two significant figures. of the U.S. Geological Survey for the analysis of waste- waters: U.S. Geological Survey Open-File Report 76-177, p. 51-60. 9. Precision Hatch, W. R., and Ott, W. L., 1968, Determination of sub- 9.1 Precision for dissolved mercury for 23 microgram quantities of mercury by atomic absorption samples within the range of 0.3 to 15.5 /ig/L spectrophotometry: Analytical Chemistry, v. 40, may be expressed as follows: p. 2085-90. U.S. Environmental Protection Agency, 1979, Methods for chemical analysis of water and wastes: Cincinnati, 0.164 p. 245.1-1. Mercury, atomic absorption spectrometric, flameless automated-sequential

Parameter and Code: Mercury, dissolved, 1-2462-85 (^g/L as Hg): 71890

1. Application maximum tolerance of 500 jug/L was obtained This method may be used to analyze water for these compounds. and wastewater containing at least 0.1 pgIL 3.4 Selenate concentrations up to 10,000 mercury. Samples containing mercury concen­ jxg/L do not interfere; higher concentrations trations greater than 8.0 /*g/L need to be were not tested. Concentrations of selenite diluted. greater than 100 jig/L interfere by suppressing the mercury absorption. 2. Summary of method 2.1 The cold-vapor, flameless, atomic ab­ 4. Apparatus sorption procedure is based on the absorption 4.1 Absorption cell, 100-mm long, 10-mm of radiation at 253.7 nm by mercury vapor. diameter, with quartz windows. Organic mercury compounds, if present, are 4.2 Atomic absorption spectrometer and decomposed by hot (95 °C) digestion with potas­ recorder or a commercial mercury analyzer. sium dichromate and potassium persulfate in 4.3 Refer to manufacturer's manual to op­ acid solution. Mercuric ions are then reduced to timize instrument for the following: the elemental state with stannous chloride, and Grating ...... Ultraviolet mercury vapor is subsequently removed from Wavelength solution by aeration and passed through a cell counter .... 253.7 nm positioned in the light path of an atomic absorp­ Source ...... Mercury-vapor, hollow- tion spectrometer. cathode, or 2.2 The method is based on a procedure electrodeless- described by El-Awady and others (1976). discharge lamp Carrier ...... Nitrogen (flow approx 3* Interferences 20 mL/min; adjust 3.1 Chloride concentrations up to 5,000 for maximum sen­ mg/L do not interfere; higher concentrations sitivity with use of a were not tested. standard) 3.2 Hydroxylamine hydrochloride-sodium 4.4 Technicon Autoanalyzer, consisting of chloride solution is added to prevent inter­ sampler, manifold (fig. 30), proportioning pump, ference from residual chlorine. and high-temperature heating bath (NOTE 1). 3.3 El-Awady and others (1976) reported NOTE 1. Nitrogen gas may be used instead of that copper sulfate (1,000 mg/L) does not in­ air in manifold (fig. 30). terfere and that chemical-oxygen-demand 4.5 Vapor-liquid separator (fig. 31). (COD) concentrations of less than 700 mg/L can be tolerated. Ethyl alcohol, methyl alcohol, 5. Reagents glycerol, chloroform, and carbon tetrachloride 5.1 Hydroxylamine kydrochhride-sodium did not interfere when added in concentrations chloride solution: Dissolve 30 g NH2OH-HC1 as high as 0.5 percent. Major interferences and 30 g NaCl in demineralized water and dilute were observed from benzene and toluene. A to 1L. 289 290 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

0.090in Wash solution 2.90 mL/min Heating bath 40- ft coil .X~N. 14-turn coil 14-turn coil ^—^ I 95 flC ) Iftflfw^1 flffffBP 0.090 in Sample f A i > 2.90 mL/min \^J 0.073in Air L ——: — r 2.00 mL/min l/ Sampler 4 Jacketed cooling Concentrated-17 20/h 27-turn coil 0.073in sulfuric acid 1/7 ram "*—————— 1 1.85 mL/min Potassium 27-turn coil '— 0.045 in dichromate 0.80 mL/min Potassium 0.045in persulfate ^-Nitrogen 0.80 mL/min Hydroxylamine 0.045in hydrochloride 0.80 mL/min sodium chloride 14-turn coil 0.073in Stannous chloride __J Vent 2.00 mL/min / i 100-mm cell (quartz windows) i——— fV ———— i Wa"" J-vC ' Proportioning pump 1 1 | Recorder 253 nm| — Red acidflex tubing AA Spectrometer Figure 30.—Mercury manifold

5.2 Mercury standard solution /, 1.00 mL = 100 /Ag Hg: Dissolve 0.1712 g Hg(NO3)2-H2O in demineralized water. Add 1.5 mL concentrated HN03 (sp gr 1.41) and 25 mL K2Cr2O7 solution,

7/251 and dilute to 1,000 mL with demineralized water. Air and solution in 0 7-cm ID 5.3 Mercury standard solution II, 1.00 mL = 1.00 /ig Hg: Dilute 10.0 mL mercury Solution standard solution I, 5 mL concentrated HNO3, out and 25 mL K2Cr2O7 solution to 1,000 mL with

0 4-cm ID demineralized water. 5.4 Mercury standard solution HI, 1.00 mL = 0.100 jig Hg: Dilute 100.0 mL mercury standard solution II, 5 mL concentrated HNO3, and 25 mL K2Cr2O7 solution to 1,000 mL with demineralized water. Use this solution to pre­ Figure 31.—Vapor-liquid separator pare working standards. The working standards METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 291 should also contain 5 mL/L of concentrated 7. Calculations HNO3 and 25 mL/L of K2Cr2O7 solution. The 7.1 Prepare an analytical curve by plotting working standards are stable for at least 3 the absorbance of each standard versus its weeks. respective mercury concentration. 5.5 Nitric acid, concentrated (sp gr 1.41), 7.2 Compute the concentration of mercury with low mercury content: Both duPont and in each sample by comparing its absorbance to Baker reagent-grade acids have been found the analytical curve. Any baseline drift that satisfactory. may occur must be taken into account when 5.6 Nitric acid (1 +99), wash solution: Dilute computing the absorbance of a sample or 10 mL of concentrated HNO3 (sp gr 1.41) to 1 standard. L with demineralized water. 5.7 Potassium dichromate solution, 20 g/L: 8. Report Dissolve 20 g K2Cr2O7 in demineralized water Report mercury, dissolved (71890), concentra­ and dilute to 1 L. tions as follows: less than 10 /tg/L, nearest 0.1 5.8 Potassium persulfate solution, 40 g/L: ftg/L; 10 /*g/L and above, two significant figures. Dissolve 40 g K2S2O8 in demineralized water and dilute to 1 L. Prepare fresh each week. 9. Precision 5.9 Stannous chloride solution, 84 g/L: 9.1 Precision for dissolved mercury for 11 Dissolve 100 g SnCl-2H2O in 100 mL concen­ samples within the range of 0.3 to 16.4 jig/L trated hydrochloric acid (sp gr 1.19) and dilute may be expressed as follows: to 1 L with demineralized water. This solution is unstable. Prepare fresh daily. Sr =0.134X+0.106 5.10 Sulfuric acid, concentrated (sp gr 1.84). where 6. Procedure ST = overall precision, micrograms per liter, 6.1 Set up manifold (fig. 30). and 6.2 Prepare a blank of demineralized water X = concentration of mercury, micrograms and sufficient standards to 8.0 /tg/L by ap­ per liter. propriate dilutions of mercury standard solu­ The correlation coefficient is 0.9722. tion III. 9.2 Precision for dissolved mercury for five 6.3 Initially feed all reagents through the of the 11 samples expressed in terms of percent system using the nitric acid wash solution in the relative standard deviation is as follows: sample line. Allow the heating bath to warm to Number of Mean Relative standard deviation 95 °C. laboratories Qtg/L) _____(percent)____ 6.4 Place a complete set of standards and a 3 0.33 17 blank in the first positions of the first sample 4 .58 54 tray, beginning with the most concentrated 3 1.87 32 3 2.80 27 standard. Place individual standards of differ­ 5 16.4 14 ing concentrations in approximately every eighth position of the remainder of this and subsequent sample trays. Fill remainder of each Reference tray with unknown samples. El-Awady, A. AM Miller, R. B.t and Carter, M. J., 1976, 6.5 Remove the sample line from the nitric Automated method for the determination of total and acid wash solution when the baseline stabilizes inorganic mercury in water and waste-water samples: and begin analysis. Analytical Chemistry, v. 48, p. 110-16.

Molybdenum, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Molybdenum, dissolved, 1-1490-85 (/tg/L as Mo): 01060 Molybdenum, total recoverable, 1-3490*85 (/xg/L as Mo): 01062 Molybdenum, suspended recoverable, I -7490-85 (pg/L as Mo): 01061 Molybdenum, recoverable-from-bottom-material, dry wt, 1-5490-85 (jig/g as Mo): 01063

1. Application to 50,000 fig/L of iron(III), 1,000 /*g/L of 1.1 This method may be used to analyze vanadium(V), and 10,000 jig/L of chromium(VI) water and water-suspended sediment contain­ or tungsten(VI) can be tolerated (Chau and ing from 1 to 50 jig/L of molybdenum. Samples Lum-Shue-Chan, 1969). containing more than 50 /*g/L need to be diluted prior to chelation-extraction. 4. Apparatus 1.2 Suspended recoverable molybdenum is 4.1 Atomic absorption spectrometer calculated by subtracting dissolved molyb­ equipped with electronic digital readout and denum from total recoverable molybdenum. automatic zero and concentration controls. 1.3 This method may be used to analyze bot­ 4.2 Refer to the manufacturer's manual to tom material containing at least 0.05 /ig/g of optimize instrument for the following: molybdenum. Prepared sample solutions con­ Grating ———————— Ultraviolet taining more than 50 tig/it of molybdenum need Wavelength ————— 313.3 nm to be diluted. Source (hollow-cathode 1.4 Total recoverable molybdenum in water- lamp) ——————— Molybdenum suspended sediment needs to undergo prelim­ Oxidant ———————— Nitrous oxide inary digestion-solubilization by method 1-3485, Fuel —————————— Acetylene and recoverable molybdenum in bottom Type of flame ———— Fuel-rich material needs to undergo preliminary diges­ 4.3 Different nitrous oxide burners may be tion-solubilization by method I-54S5 before be­ used according to manufacturers' instructions. ing determined. 5. Reagents 2. Summary of method 5.1 Ascorbic acid solution, 1 g/100 mL: Dis­ Molybdenum is determined by atomic absorp­ solve 1 g ascorbic acid in 100 mL demineralized tion spectrometry following chelation with water. 8-hydroxyquinoline and extraction with methyl 5.2 Bromophenol blue indicator solution* 0.1 isobutyl ketone (MIBK). The extract is aspi­ g/100 mL: Dissolve 0.1 g bromophenol blue in rated into a nitrous oxide-acetylene flame of the 100 mL 50-percent ethanol. spectrometer (Chau and Lum-Shue- Chan, 1969). 5.3 Hydrochloric acid, 0.3M: Mix 25 mL con­ centrated HC1 (sp gr 1.19) with demineralized 3. Interferences water and dilute to 1 L. The method is free from interference from 5.4 8-Hydroxyquinoline-methyl isobutyl most elements commonly found in fresh water. ketone solution, 1 g/100 mL: Dissolve 1 g 8- Vanadium(V) and iron(III) enhance the absorp­ hydroxyquinoline in 100 mL MIBK. Prepare tion, and chromium(VI) and tungsten(VI) sup­ fresh daily. press it. With the addition of ascorbic acid, up 5.5 Methyl isobutyl ketone (MIBK). 293 294 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.6 Molybdenum standard solution /, 1.00 6.9 While aspirating the ketone layer of the mL = 100 pig Mo: Dissolve 0,1500 g reagent- blank, use the automatic zero control to set the grade MoO3 in 10 mL 0.1M NaOH (warm if digital display to read zero concentration. While necessary). Make just acidic with 0.1M HC1 and aspirating standards, use the automatic concen­ dilute to 1,000 mL with demineralized water. tration control to set the digital display to read 5.7 Molybdenum standard solution //, 1.00 the concentration of the standards. Use at least mL = 1.0 pig Mo: Dilute 10.0 mL molybdenum six standards. Calibrate the instrument each standard solution I to 1,000 mL with time a set of samples is analyzed and check demineralized water. calibration at reasonable intervals. 5.8 Molybdenum standard solution ///, 1.0 mL = 0.10 ^g Mo: Immediately before use, 7. Calculations dilute 10.0 mL molybdenum standard solution 7.1 Determine the micrograms per liter of II to 100 mL with demineralized water. This dissolved or total recoverable molybdenum in standard is used to prepare working standards each sample from the digital display or printer. at the time of analysis. Dilute those samples containing molybdenum 5.9 Sodium hydroxide solution, 2.5M: concentrations that exceed the working range Dissolve 100 g NaOH in demineralized water of the method; repeat the chelation-extraction and dilute to 1 L. and multiply by the proper dilution factors. 7.2 To determine micrograms per liter of 6. Procedure suspended recoverable molybdenum, subtract 6.1 Clean all glassware used in this deter­ dissolved-molybdenum concentration from mination with warm, dilute HNO3 (1+9), and total-recoverable-molybdenum concentration. rinse with demineralized water immediately 7.3 To determine micrograms per gram of before use. molybdenum in bottom-material samples, first 6.2 Pipet a volume of sample or prepared determine the micrograms per liter of sample solution containing less than 5.0 ug Mo molybdenum as in paragraph 7.1; then (100 mL max) into a 200-mL volumetric flask, and adjust the volume to approx 100 mL. 6.3 Prepare a demineralized-water blank mL of original digest with 1.5 mL concentrated. HNO3 per liter of Mo X demineralized water and at least six standards, Mo (jig/g) = _____1,000____ and adjust the volume of each to approx 100 mL wt of sample (g) with demineralized water. 6.4 Add 5 mL ascorbic acid solution and mix. 8. Report 6.5 Add 2 drops bromophenol blue indicator 8.1 Report molybdenum, dissolved (01060), solution and mix. total recoverable (01062), and suspended 6.6 Adjust the pH by addition of 2.5M recoverable (01061), concentrations as follows: NaOH until a blue color persists. Add 0.3M HC1 less than 100 ftg/L, nearest microgram per liter; by drops until the blue color just disappears; 100 /ig/L and above, two significant figures. then add 2.0 mL 0.3M HC1 in excess. The pH 8.2 Report molybdenum, recoverable-from- at this point should be 2.3 (NOTE 1). bottom-material (01063), concentrations as NOTE 1. The pH adjustment in paragraphs 6.5 follows: less than 10 pg/g, nearest 0.1 /*g/g; 10 and 6.6 may be made using a pH meter instead and above, two significant figures. of using indicator. Add 2.5M NaOH to the solu­ tion until the pH is 2.3. 9. Precision 6.7 Add 5.0 mL 8-hydroxyquinoline-MIBK 9.1 Precision for dissolved molybdenum for solution and shake vigorously for 15 min. seven samples within the range of 1.3 to 56.7 6.8 Allow the layers to separate; then add /ig/L may be expressed as follows: demineralized water until the ketone layer is completely in the neck of the flask. .320 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 295 where 9.3 It is estimated that the percent relative ST = overall precision, micrograms per liter, standard deviation for total recoverable and and, suspended recoverable molybdenum and for X = concentration of molybdenum, micro- recoverable molybdenum in bottom material will grams per liter. be greater than that reported for dissolved The correlation coefficient is 0.8718. molybdenum. 9.2 Precision for dissolved molybdenum for four of the seven samples expressed in terms of the percent relative standard deviation is as follows: Reference Number of Mean Relative standard deviation laboratories _____(percent) _____ Chau, Y. K., and Lum-Shue-Chan, K., 1969, Atomic absorp­ 3 1.3 115 5 2.0 35 tion determination of microgram quantities of 4 25.2 17 molybdenum in lake waters: Analytical Chimica Acta, 3 56.7 8 v. 48, p. 205.

Molybdenum, atomic emission spectrometric, ICP

Parameter and Code: Molybdenum, dissolved, 1-1472-85 fcig/L as Mo): 01060

2. Summary of method method utilizing an induction-coupled argon Molybdenum is determined simultaneously plasma as an excitation source. See method with several other constituents on a single sam­ 1-1472, metals, atomic emission spectrometric, ple by a direct-reading emission spectrometric ICP. 297

Nickel, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: • Nickel, dissolved, 1-1500-85 G*g/L as Ni): 01065 Nickel, total recoverable, I-3500-85 fcg/L as Ni): 01067 Nickel, suspended recoverable, I-7500-85 Oig/L as Ni): 01066

1. Application 4.2 Refer to the manufacturer's manual to 1.1 This method may be used to analyze optimize instrument for the following: water, brines, and water-suspended sediment Grating ———————— Ultraviolet containing from 1 to 100 pig/L of nickel. Sam­ Wavelength ————— 232.0 nm ple solutions containing more than 100 jtg/L (NOTES 1 need either to be diluted prior to chelation- and 2) extraction or to be analyzed by the atomic ab­ Source (hollow-cathode sorption direct method. lamp) ———————— Nickel 1.2 Suspended recoverable nickel is Oxidant ———————— Air calculated by subtracting dissolved nickel from Fuel —————————— Acetylene total recoverable nickel. Type of flame ———— Oxidizing 1.3 Total recoverable nickel in water-sus­ NOTE 1. Setting the proper wavelength for pended sediment needs to undergo a prelim­ nickel is critical because of the presence of an inary digestion-solubilization by method 1-3485 ion line at 231.6 nm. By aspirating a standard before being determined. that gives approx 50-percent absorption, the 1.4 If the iron concentration of the sample 232.0-nm absorption line can easily be set. solution exceeds 25,000 jug/L, determine nickel NOTE 2. The 352.4-nm wavelength, less suscep­ by the atomic absorption spectrometric direct tible to nonatomic absorbance, may be used. method. The resulting analytical curve is more nearly linear; however, the procedure reduces sen­ 2. Summary of method sitivity. Nickel is determined by atomic absorption 4.3 Different burners may be used according spectrometry following chelation with am­ to manufacturers' instructions. monium pyrrolidine dithiocarbamate (APDC) and extraction with methyl isobutyl ketone 5. Reagents (MIBK). The extract is aspirated into the air- 5.1 Ammonium pyrrolidine dithiocarbamate acetylene flame of the spectrometer (Fishman solution, 1 g/100 mL: Dissolve 1 g APDC in 100 and Midgett, 1968). mL demineralized water. Prepare fresh daily. 5.2 Citric acid-sodium citrate buffer solution: 3. Interferences Dissolve 126 g citric acid monohydrate and 44 Concentrations of iron greater than 25,000 /xg/L g sodium citrate dihydrate in demineralized interfere by suppressing the nickel absorption. water and dilute to 1 L with demineralized water. See NOTE 5 before preparation. 4. Apparatus 5.3 Methyl isobutyl ketone (MIBK). 4.1 Atomic absorption spectrometer 5.4 Nickel standard solution /, 1.00 mL = equipped with electronic digital readout and 200 fig Ni: Dissolve 0.2000 g nickel powder in automatic zero and concentration controls. a minimum amount of dilute HNO3. Heat to 299 300 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS increase rate of dissolution. Add 10.0 mL con­ demineralized water until the ketone layer is centrated HNO3 (sp gr 1.41) and dilute to 1,000 completely in the neck of the flask. mL with demineralized water. 6.8 Aspirate the ketone layer within 1 h. As­ 5.5 Nickel standard solution II, 1.00 mL = pirate the ketone layer of the blank to set the 2.00 /ig Ni: Dilute 10.0 mL nickel standard solu­ automatic zero control. Use the automatic con­ tion I and 1 mL concentrated HNO3 to 1,000 centration control to set the concentrations of mL with demineralized water. This solution is standards. Use at least six standards. Calibrate used to prepare working standards at the time the instrument each time a set of samples is of analysis. analyzed and check calibration at reasonable in­ 5.6 Potassium hydroxide, 10M: Dissolve 56 tervals. g KOH in demineralized water, cool, and dilute to 100 mL. 7. Calculations 5.7 Potassium hydroxide, 2.5M: Dissolve 14 7.1 Determine the micrograms per liter of g KOH in demineralized water and dilute to 100 dissolved or total recoverable nickel in each mL (NOTE 3). sample from the digital display or printer while NOTE 3. Alternatively, a 2.5M NH4OH solu­ aspirating each sample. Dilute those samples tion may be used. Add 167 mL concentrated containing concentrations of nickel that exceed NH4OH (sp gr 0.90) to 600 mL demineralized the working range of the method; repeat the water. Cool, and dilute to 1 L. chelation-extraction and multiply by the proper 5.8 Water, acidified: Add 1.5 mL concen­ dilution factors. trated HNO3 (sp gr 1.41) to 1L of demineralized 7.2 To determine the micrograms per liter of water. suspended recoverable nickel, subtract dis- solved-nickel concentration from total-recover­ 6. Procedure able-nickel concentration. 6.1 Clean all glassware used in this deter­ mination with warm, dilute HNO3 (1+9) and 8. Report rinse with demineralized water immediately Report nickel, dissolved (01065), total-recover­ before use. able (01067), and suspended-recoverable (01066), 6.2 Pipet a volume of sample solution con­ concentrations as follows: less than 10 /*g/L, taining less than 10 pg Ni (100 mL max) into nearest microgram per liter; 10 jtg/L and above, a 200-mL volumetric flask, and adjust the two significant figures. volume to approx 100 mL. 6.3 Prepare a blank of acidified water and 9. Precision sufficient standards, and adjust the volume of 9.1 The standard deviation for dissolved each to approx 100 mL with acidified water. nickel within the range of 3.8 to 23.2 pgIL for 6.4 With a pH meter, adjust the pH of each 20 samples was found to be independent of con­ solution to 2.4 with 2.5M KOH (NOTES 4 and centration. The 95-percent confidence interval 5). Shake for 3 min. for the average standard deviation of 4.3 /*g/L NOTE 4. For water-suspended sediment ranged from 3.8 to 5.0 ftg/L. samples that have been digested, add 1 to 2 mL 9.2 Precision for dissolved nickel for five of lOAf KOH or concentrated NH4OH (sp gr 0.90) the 20 samples expressed in terms of the before pH adjustment. percent relative standard deviation is as NOTE 5. If an automated titration system is follows: used to adjust the pH, add 2.5 mL citric acid- sodium citrate buffer solution prior to pH ad­ justment. This will prevent over-shooting the Number of Mean Relative standard deviation end point in poorly buffered samples. laboratories 0*g/L) _____(percent)_____ 6.5 Add 2.5 mL APDC solution and mix. 5 3.8 11 6.6 Add 10.0 mL MIBK and shake vigorous­ 5 4.4 61 4 10.2 38 ly for 3 min. 8 10.5 16 6.7 Allow the layers to separate and add 13 23.2 23 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 301 9.3 It is estimated that the percent relative Reference standard deviation for total-recoverable and Fishman, M. J., and Midgett, M. R., 1968, Extraction tech­ suspended recoverable nickel will be greater niques for the determination of cobalt, nickel, and lead in fresh water by atomic absorption, in Trace inorganics than that reported for dissolved nickel. in water: American Chemical Society Advances in Chemistry Series, no. 73, p. 230-5.

Nickel, atomic absorption spectrometric, direct

Parameters and Codes: Nickel, dissolved, 1-1499-85 (/xg/L as Ni): 01065 Nickel, total recoverable, I-3499-85 {^g/L as Ni): 01067 Nickel, suspended recoverable, 1-7499-85 (/*g/L as Ni): 01066 Nickel, recoverable-from-bottom-material, dry wt, I -5499-85 Oig/g as Ni): 01068

1. Application mg/L), and cadmium, lead, copper, zinc, cobalt, 1.1 This method may be used to analyze water and chromium (10,000 /xg/L each) do not in­ and water-suspended sediment containing at terfere. Higher concentrations of each consti­ least 100 /ig/L of nickel. Sample solutions con­ tuent were not investigated. taining more than 1,000 itglL need either to be diluted or to be read on a less expanded scale. 4. Apparatus Sample solutions containing less than 100 jig/L 4.1 Atomic absorption spectrometer and brines need to be analyzed by the atomic equipped with electronic digital readout and absorption spectrometric chelation-extraction automatic zero and concentration controls. method, providing that the interference limits 4.2 Refer to the manufacturer's manual to discussed in that method are not exceeded. optimize instrument for the following: 1.2 Suspended recoverable nickel is calcu­ Grating ———————— Ultraviolet lated by subtracting dissolved nickel from total Wavelength ————— 232.0 nm recoverable nickel. (NOTES 1 1.3 This method may be used to analyze bot­ and 2) tom material containing at least 5.0 jig/g of Source (hollow-cathode nickel. Sample solutions containing more than lamp) --—————— Nickel 1,000 figlL need either to be diluted or to be read Oxidant ———————— Air on a less expanded scale. Fuel ————————— Acetylene 1.4 Total recoverable nickel in water-sus­ Type of flame ———— Oxidizing pended sediment needs to undergo preliminary NOTE 1. Setting the proper wavelength for digestion-solubilization by method 1-3485, and nickel is critical because of the presence of an recoverable nickel in bottom material needs to ion line at 231.6 nm. By aspirating a standard undergo preliminary digestion-solubilization by that gives approx 50-percent absorption, the method 1-5485 before being determined. 232.0 nm-absorption line can easily be set. NOTE 2. The 352.4-nm wavelength, less suscep­ 2. Summary of method tible to nonatomic absorbance, may be used. Nickel is determined by atomic absorption The resulting analytical curve is more nearly spectrometry by direct aspiration of the sam­ linear; however, the procedure reduces sen­ ple into an air-acetylene flame without precon- sitivity. centration or pretreatment. 5. Reagents 3. Interferences 5.1 Nickel standard solution /, 1.00 mL = Individual concentrations of sodium (9,000 200 jig Ni: Dissolve 0.2000 g Ni powder in mg/L), potassium (9,000 mg/L), calcium (4,000 a minimum amount of dilute HNO3. Heat to mg/L), magnesium (4,000 mg/L), sulfate (9,000 increase rate of dissolution. Add 10.0 mL

303 304 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS concentrated HNO3 (sp gr 1.41) and dilute to (01066), concentrations to the nearest 100 /*g/L. 1,000 mL with demineralized water. 8.2 Report nickel, recoverable-from-bottom- 5.2 Nickel standard solution II, 1.00 mL = material (01068), concentrations as follows: less 20 ^g Ni: Dilute 100 mL nickel standard solu­ than 100 jxg/g, nearest 10 jig/g; 100 pglg and tion I and 1 mL concentrated HNO3 (sp gr 1.41) above, two significant figures. to 1,000 mL with demineralized water. 5.3 Nickel standard working solutions: 9. Precision Prepare a series of at least six standard work­ 9.1 Precision for dissolved nickel for 16 ing solutions containing from 100 to 1,000 /*g/L samples within the range of 6.2 to 36.2 /ig/L of nickel by appropriate dilution of nickel stand­ (NOTE 3) may be expressed as follows: ard solution II with acidified water. Prepare fresh daily. ST = 0.431X + 2.88 5.4 Water, acidified: Add 1.5 mL concen­ trated HNO3 (sp gr 1.41) to 1 L of demineral­ where ized water. ST = overall precision, micrograms per liter, and 6. Procedure X = concentration of nickel, micrograms per Aspirate the blank (acidified water) to set the liter. automatic zero control. Use the automatic con­ The correlation coefficient is 0.7593. centration control to set the concentrations of NOTE 3. Precision data for nickel are below the standards. Use at least six standards. Calibrate reporting level of 100 /*g/L. Samples were not the instrument each time a set of samples is available that contained greater nickel concen­ analyzed and check calibration at reasonable in­ trations; however, precision should improve at tervals. greater concentrations. 9.2 Precision for dissolved nickel for five of 7. Calculations the 16 samples expressed in terms of the per­ 7.1 Determine the micrograms per liter of cent relative standard deviation is as follows: dissolved or total recoverable nickel in each sample from the digital display or printer while Number of Mean Relative standard deviation aspirating each sample. Dilute those samples laboratories _____(percent)_____ containing concentrations of nickel that exceed 5 6.2 18 the working range of the method and multiply 11 10.5 80 6 10.8 15 by the proper dilution factors. 6 20.0 46 7.2 To determine micrograms per liter of 19 36.2 47 suspended recoverable nickel, subtract dis- solved-nickel concentration from total-recover­ able-nickel concentration. 9.3 It is estimated that the percent relative 7.3 To determine micrograms per gram of standard deviation for total recoverable and nickel in bottom-material samples, first deter­ suspended recoverable nickel and for nickel in mine the micrograms per liter of nickel as in bottom material will be greater than that paragraph 7.1; then reported for dissolved nickel. 9.4 Precision for total recoverable nickel ex­ mL of original digest Ni X pressed in terms of the percent relative stan­ Ni 1,000 dard for two water-suspended sediments is as wt of sample (g) follows:

Number of Mean Relative standard deviation 8. Report laboratories _____(percent)______8.1 Report nickel, dissolved (01065), total- 10 26.2 58 recoverable (01067), and suspended* recoverable 10 35.9 53 Nickel, atomic absorption spectrometric, graphite furnace

Parameter and Code: Nickel, dissolved, 1-1501-85 0*g/L as Ni): 01065

1. Application (20 mg/L), sulfate (34 mg/L), and chloride (25 1.1 This method may be used to determine mg/L) do not interfere. Higher concentrations nickel in low ionic-strength water and precipita­ of these constituents were not investigated. tion. With deuterium background correction 3.2 Precipitation samples usually contain and a 20-/*L sample, the method is applicable very low concentrations of nickel. Special in the range from 1 to 100 Mg/L. With Zeeman precautionary measures must be employed dur­ background correction and a 20-^L sample, the ing both sample collection and laboratory deter­ method is applicable in the range from 1 to 80 mination to prevent contamination. jtg/L. Sample solutions that contain nickel con­ centrations exceeding the upper limits must be 4. Apparatus diluted or preferably be analyzed by the atomic 4.1 Atomic absorption spectrometer* for use absorption spectrometric direct or chelation- at 232.0 ran and equipped with background cor­ extraction method. rection, digital integrator to quantitate peak 1.2 The analytical range and detection limits areas, graphite furnace with temperature pro­ can be increased or possibly decreased by vary­ grammer, and automatic sample injector. The ing the volume of sample injected or the in­ programmer must have high-temperature ramp­ strumental settings. Purification of reagents ing and stopped-flow capabilities. and use of ASTM Type 1 water (Method 4.1.1 Refer to the manufacturer's manual to D-1193, American Society for Testing and optimize instrumental performance. The Materials, 1984) may result in lower detection analytical ranges reported in paragraph 1.1 are limits. for a 20-jiL sample (NOTE 1). NOTE 1. A 20-jiL sample generally requires 30 2. Summary of method s to dry. Samples that have a complex matrix Nickel is determined by atomic absorption may require a longer drying and charring time. spectrometry in conjunction with a graphite fur­ 4.1.2 Graphite furnace, capable of reaching nace containing a graphite platform (Hinder- temperatures sufficient to atomize the element berger and others, 1981). A sample is placed on of interest. Warning: dial settings frequently the graphite platform, and the sample is then are inaccurate and newly conditioned furnaces evaporated to dryness, charred, and atomized require temperature calibration. using high-temperature ramping. The absorp­ 4.1.3 Graphite tubes and platforms. Pyro- tion signal generated during atomization is lytically coated graphite tubes and solid pyro- recorded and compared with standards. lytic graphite platforms are recommended. 4.2 Labware. Many trace metals at very low 3. Interferences concentrations have been found to sorb very 3.1 Interferences in low ionic-strength sam­ rapidly to glassware. To preclude this, fluorin- ples, such as precipitation,normally are quite ated ethylene propylene (FEP) or Teflon lab- low. In addition, the use of the graphite plat­ ware may be used. Alternately, glassware, form reduces the effects of many interferences. particularly flasks and pipets, may be treated Calcium (25 mg/L), magnesium (8 mg/L), sodium with silicone anti-wetting agent such as Surfacfl 305 306 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS (Pierce Chemical Co,, Rockford, IL, 61105) ac­ high purity concentrated HNO3 (sp gr 1.41) to cording to the manufacturer's instructions. each liter of water. Autosampler cups must be checked for con­ 5.7 Water, Type 1. tamination. Lancer (1831 Olive St., St. Louis, MO, 63103) polystyrene disposable cups have 6. Procedure been found to be satisfactory after acid rinsing. 6.1 Systematically clean and rinse work Alternately, reuseable Teflon or FEP cups may areas with deionized water on a regular sched­ be used. ule. Use a laminar flow hood or a "clean room" 4.3 Argon, standard, welder's grade, com­ environment during sample transfers. Ideally, mercially available. Nitrogen may also be used the autosampler and the graphite furnace if recommended by the instrument should be in a clean environment. manufacturer. 6.2 Soak autosampler cups at least over­ night in a 1+1 solution of Type 1 water and 5. Reagents high-purity nitric acid. 5.1 Nickel standard solution /, 1.00 mL = 6.3 Rinse the sample cups twice with sam­ 1,000 /tg Ni: Dissolve 1.0000 g Ni powder in a ple before filling. Place cups in sample tray and minimum of dilute HNO3. Heat to increase rate cover. Adjust sampler so that only the injection of dissolution. Add 10 mL high-purity, concen­ tip contacts the sample. trated HNO3 (sp gr 1.41), Ultrex or equivalent, 6.4 In sequence, inject 20-/*L aliquots of and dilute to 1,000 mL with Type 1 water. blank and working standards, and analyze. 5.2 Nickel standard solution II, 1.00 Analyze the blank and working standards twice. mL — 10.0 /tg Ni: Dilute 10.0 mL nickel stand­ Construct the analytical curve from the in­ ard solution I to 1,000 mL (NOTE 2). tegrated peak areas (absorbance-seconds). NOTE 2. Use acidified Type 1 water (paragraph Generally, the curve should be linear to a peak- 5.6) to make dilutions. All standards must be absorbance (peak-height) value of 0.40 absorb- stored in sealed Teflon or FEP containers. Each ance units. container must be rinsed twice with a small 6.5 Similarly, inject and analyze the samples volume of standard before being filled. Stand­ twice. Every tenth sample cup should contain ards stored for 6 months in FEP containers either a standard or a reference material. yielded values equal to those of freshly prepared 6.6 Restandardize as required. Minor standards. changes of values for known samples usually in­ 5.3 Nickel standard solution III, 1.00 mL = dicate deterioration of the furnace tube, contact 1.00 fig Ni: Dilute 100.0 mL nickel standard rings, and (or) platform. A major variation solution II to 1,000 mL. This standard is used usually indicates either autosampler malfunc­ to prepare working standards serially at time tion or residue buildup from a complex matrix of analysis. in a previous sample. 5.4 Nickel standard solution IV, 1.00 mL = 0.010 fug Ni: Dilute 10.0 mL nickel standard 7. Calculations solution III to 1,000 mL. This standard also is Determine the micrograms per liter of nickel used to prepare working standards serially at in each sample from the digital display or time of analysis. printer output. Dilute those samples containing 5.5 Nitric acid, concentrated, high-purity, concentrations of nickel that exceed the work­ (sp gr 1.41): J. T. Baker "Ultrex" brand HNO3 ing range of the method; repeat the analysis, has been found to be adequately pure; however, and multiply by the proper dilution factors. each lot must be checked for contamination. Analyze acidified Type 1 water for nickel. Add 8. Report an additional 1.5 mL of concentrated Report nickel, dissolved (01065), concentra­ HNO3/liter of water, and repeat analysis. The tions as follows: less than 10 /*g/L, nearest 1 integrated signal should not increase by more /ig/L; 10 /xg/L and above, two significant figures than 0.001 absorbance-seconds. for both deuterium background correction and 5.6 Water, acidified, Type 1: Add 1,5 mL Zeeman background correction. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 307

9. Precision Relative 9.1 Analysis of two samples by a single Amount < Amount Standard standard added found deviation deviation Recovery operator using deuterium background correc­ Otg/L) 0*9/1-) (/*0/L) (percent) (percent) tion is as follows: Deionized water Relative standard 4.35 3.8 1.0 26.3 87 Number of Mean Standard deviation deviation 8.7 9.0 .6 6.7 103 replicates 0*9/L) fcg/U (percent) 13 13.2 1.2 9.1 102 26 25.5 3.1 12.2 98 10 5.8 0.6 10.3 27.5 23.2 1.7 7.3 84 5 9.8 .8 8.2 Tap water (NOTE 3) 9.2 Analysis of three samples six times each 4.35 5.7 .8 11.6 131 by a single operator using Zeeman background 8.7 9.8 .6 5.5 113 correction is as follows: 13 12.8 1.3 9.3 98 26 22.5 3.1 13.0 87 Mean Standard deviation Relative standard deviation 27.5 24.1 2.7 10.9 88 0*g/L) (/*9/L) (percent) 14.5 0.6 4.1 48.3 .5 1.0 9.5 The standard deviation from inter- 79.7 .5 .6 laboratory data, without regard to type of 9.3 The precision and bias for the Zeeman background correction and use of matrix background correction were tested on deionized modifiers, if any, for dissolved nickel within the water and tap water (specific conductance 280 range of 3.8 to 22.5 /*g/L for 16 samples was /xS/cm). A known amount of nickel was added found to be independent of concentration. The to each sample, and single-operator precision 95-percent confidence interval for the average and bias for six replicates are as follows: standard deviation of 5.2 /tg/L ranged from 4.5 to 6.1 A*g/L-

Relative Amount Amount Standard standard added found deviation deviation Recovery References (pQ/L) W-) G*Q/U (percent) (percent) Deionized water American Society for Testing and Materials, 1984, Annual 4.35 4.0 0.6 16 92 book of ASTM standards, section 11, water: Philadel­ 8.7 9.3 .5 5 107 phia, American Society for Testing and Materials, 13 12.3 .8 7 95 v. 11.01, p. 39-41. 26 24.5 1.6 6 94 Cooksey, M., and Barnett, W. B., 1979, Matrix modifica­ 27.5 22.8 1.5 7 83 tion and the method of additions in flameless atomic Tap water (NOTE 3) absorption: Atomic Absorption Newsletter, v. 18, p. 101-5. 4.35 4.2 .8 15 97 Fernandez, F. J., Beatty, M. MM and Barnett, W. B., 1981, 8.7 9.6 .8 7 110 Use of the L'vov platform for furnace atomic absorp­ 13 12.0 1.0 7 92 tion applications: Atomic Spectroscopy, v. 2, p. 16-21. 26 21.5 1.5 7 83 Hinderberger, E. J., Kaiser, M. L., and Koirtyohann, S. R., 27.5 24.1 1.9 8 88 1981, Furnace atomic absorption analysis of biological samples using the L'vov platform and matrix modifica­ NOTE 3. The tap water contained 1.2 ^g/L of tion: Atomic Spectroscopy, v. 2, p. 1-11. nickel, and the standard deviation and percent Manning, D. C., and Slavin, W., 1983, The determination of trace elements in natural waters using the stabilized relative standard deviation were calculated temperature platform furnace: Applied Spectroscopy, prior to subtraction of nickel originally present. v. 37, p. 1-11. 9.4 The precision and bias for the deuterium Ottaway, J. M., 1982, A revolutionary development in background method were tested on deionized graphite furnace atomic absorption: Atomic Spectro­ water and tap water (specific conductance 280 scopy, v. 3, p. 89-92. Slavin, W., Carnrick, G. R,, and Manning, D. C., 1982, /iS/cm). A known amount of nickel was added Magnesium nitrate as a matrix modifier in the stabilized to each sample, and single-operator precision temperature platform furnace: Analytical Chemistry, and bias for six replicates are as follows: v. 54, p. 621-4.

Nickel, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Nickel, total, 1-5474-85 (mg/kg as Ni): none assigned

2. Summary of method hotplate at 200 °C. Nickel is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec- homogenized. The sample is digested with a trometry. See method 1-5474, metals, major and combination of nitric, hydrofluoric, and per­ minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a spectrometric, direct. 309

Nitrogen, titrimetric, digestion-distillation

Parameter and Code: Nitrogen, total-in-bottom-material, dry wt, 1-5554-85 (mg/kg as N): 00603

1. Application 5.5 Salicylic acid, crystals. This method may be used to determine the 5.6 Sodium carbonate solution, 0.03577V: Dis­ total nitrogen concentration of any sample of solve 1.892 g primary standard Na2CO3 in cai> bottom material containing at least 20 mg/kg. bon dioxide-free water and dilute to 1,000 xnL. Only that portion of bottom material that 5.7 Sodium hydroxide-tkiosulfate solution: passes a 2-mm sieve is taken for analysis. With care, dissolve 500 g NaOH in 600 mL ammonia-free water. Add 80 g Na2S2O3-5H2O 2. Summary of method and dilute to 1 L. Salicylic acid in concentrated sulfuric acid is 5.8 Sodium thiosulfate, crystals Na2S2O3- added to the sample of bottom material The 5H2O. sample is then subjected to a digestion whereby 5.9 Sucrose. all nitrogen-containing compounds are converted 5.10 Sulfuric acid, concentrated, sp gr 1.84. to ammonium salts. The resulting mixture is then 5.11 Sulfuric acid standard solution, approx made strongly alkaline, and the ammonia so 0.036AT: Cautiously add 1.0 mL concentrated formed is distilled from the mixture into a solu­ H2SO4 (sp gr 1.84) to 800 mL ammonia-free tion of boric acid and subsequently determined water and dilute to 1 L. Standardize by titrating by titration with standard sulfuric acid solution. 25.0 mL 0.035AT Na^Og to pH 4.5, Compute normality of sulfuric acid standard solution to 3. Interferences four decimal places. There are no known interferences with this method. 6. Procedure 6.1 Free the distillation apparatus of am­ 4. Apparatus monia by boiling ammonia-free water until the Kjeldahl distillation apparatus, 500-mL distillate shows no trace using nessler reagent— flasks. CAUTION: deadly poison. (See nitrogen, am­ monia, colorimetric, distillation-nesslerization 5. Reagents method.) 5.1 Ammonium chloride, crystals. 6.2 Weigh, to the nearest milligram, 3 g of 5.2 Boric acid solution, 20 g/L: Dissolve 20 bottom-material sample, prepared as directed in g H3BO3 crystals in 800 mL ammonia-free method P-0810 (subsampling, bottom-material, water and dilute to 1 L. coring), and transfer to the digestion flask. 5.3 Digestion catalyst: Tablets containing 6.3 Prepare a blank and standard, using 2.0 3.5 g K2SO4 and 0.175 g HgO (Scientific g sucrose for the blank and 0.1000 g NH4C1 Chemical Sales Inc., Kel-catalyst Na KC-M3 or plus 2.0 sucrose for the standard. equivalent), 6.4 Cautiously, add 25 mL concentrated 5.4 Mixed indicator solution: Dissolve 20 mg H2SO4 (sp gr 1.84), and then add 1.0 g salicylic methyl red and 100 mg bromocresol green in 100 acid. Under a hood, swirl the contents of each mL 95-percent ethanol. Store in a well-sealed flask until thoroughly mixed. Allow to stand for bottle. at least 30 min. 311 312 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6.5 Under a hood, add 5 g Na2S2O3'5H2O 6.11 Collect approx 200 mL of distillate, dilute and heat gently over a Bunsen burner. Let to 250 mL with ammonia-free water, and mix. stand for about 5 nmin or until any frothing 6.12 Add 3 drops mixed indicator solution to ceases. the distillate and titrate with standard H2SO4 6.6 Add three digestion-catalyst tablets and until the solution changes from yellow to red. mix well. Add a few glass beads and begin the digestion. Continue the digestion until a clear 7. Calculations solution is obtained, and then continue fuming 1 h. Nitrogen, total, mg/kg = ———=—————Va X Na X 14,000 6.7 Cool the flask until crystals appear. (Do Wts not cool completely). Add 150 mL ammonia-free water; mix and allow to cool. where 6.8 To avoid bumping during the subse­ Va =volume of standard H2SO4 used to quent distillation, transfer the entire solution titrate sample, milliliters, minus volume from the digestion flask to a clean Kjeldahl used to titrate blank, milliliters, flask. Rinse the digestion flask with a minimum Na = normality of standard H2SO4 solution, of ammonia-free water and add to the contents and of the clean flask. Wts = weight of sample, grams. 6.9 Add 100 mL NaOH-Na2S2O3 solution. Immediately connect the flask to the distillation 8. Report apparatus and cautiously mix the contents by Report nitrogen, total in bottom material swirling. (00603), as follows: less than 100 mg/kg, nearest 6.10 Distill at a rate of not more than 10 10 mg/kg; 100 mg/kg and above, two significant mL/min or less than 6 mL/min; collect the figures. distillate in a 250-mL volumetric flask contain­ ing 25 mL boric acid solution. The tip of the 9. Precision delivery tube must be below the surface of the Precision data are not available for this boric acid solution in the receiving flask. method. Nitrogen, ammonia, colorimetric, distillation-nesslerization

Parameters and Codes: Nitrogen, ammonia, dissolved, 1-1520-85 (mg/L as N): 00608 Nitrogen, ammonia, total, I-3520-85 (mg/L as N): 00610

1. Application with the spectrophotometer. Under such condi­ This method may be used to analyze water tions, the sample should be titrated with stand­ and water-suspended sediment containing from ard sulfuric acid solution. 0.01 to 2 mg/L of ammonia-nitrogen. Samples containing more than 2 mg/L need either to be 4. Apparatus diluted or to be analyzed by an alternative titra- 4.1 Cylinder, graduated, with ground-glass tion procedure. stopper, 50-mL capacity (Corning No. 3002 or equivalent). 2. Summary of method 4.2 Kjeldahl distillation apparatus, 500-mL 2.1 The sample is buffered to a pH of 9.5 to flasks. minimize hydrolysis of organic nitrogen com­ 4.3 Spectrophotometer, for use at 425 nm. pounds. Ammonia is distilled from the buffered 4.4 Refer to the manufacturer's manual to solution, and an aliquot of the distillate then is optimize instrument. nesslerized. Essentially, nesslerization is the reaction between potassium mercuric iodide and 5. Reagents ammonia to form a red-brown colloidal complex 5.1 Ammonia standard solution I, 1.00 of mercuric ammonobasic iodide: mL = 1.00 mg NH3-N: Dissolve 3.819 g NH4C1, dried overnight over sulfuric acid, in 2(HgI2-2KI) ammonia-free water and dilute to 1,000 mL. 5.2 Ammonia standard solution II, 1.00 NH2Hg2I3 + 4KI + NH4I mL = 0.010 mg NH3-N: Dilute 10.0 mL am­ monia standard solution I to 1,000 mL with Concentrations of ammonia are then determined ammonia-free water. Prepare fresh daily. by standard spectrometric measurements. 5.3 Borate buffer solution: Dissolve 9.54 g Alternatively, the distillate may be titrated Na2B4O7-10H2O in ammonia-free water. Adjust with standard sulfuric acid solution. the pH to 9.5 with IM NaOH (approx 15 mL) 2.2 Additional information on the principle and dilute to 1 L with ammonia-free water. of the determination was given by Blaedel and 5.4 Boric acid solution, 20 g/L: Dissolve 20 Meloche (1963). g H3BO3 in 800 mL ammonia-free water and dilute to 1 L. 3. Interferences 5.5 Nessler reagent—CAUTION: HgI2 is a 3.1 Calcium, magnesium, iron, and sulfide deadly poison, and the reagent must be so interfere with the nesslerization, but the in­ marked: Dissolve 100 g HgI2 and 70 g KI in a terference of the metals is eliminated by the small volume of ammonia-free water. Add this distillation, and sulfide can be precipitated in mixture slowly, with stirring, to a cooled solu­ the distillation flask by lead carbonate. tion of 160 g NaOH in 500 mL ammonia- free 3.2 Some organic compounds may distill water and dilute to 1 L. Allow the reagent to with the ammonia and form colors with nessler stand at least overnight and filter through a reagent, which cannot satisfactorily be read fritted-glass crucible. 313 314 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.6 Sodium hydroxide solution, 1M: Dissolve 7.2 Determine the ammonia-nitrogen con­ 40 g NaOH in ammonia-free water and dilute to centration in milligrams per liter as follows: 1 L. Ammonia-nitrogen as N, (mg/L) = 6. Procedure 6.1 Rinse all glassware with ammonia-free ——————1,000 X ——————250 X mg N in aliquot water before beginning this determination. mL sample mL aliquot 6.2 Free the distillation apparatus of am­ monia by boiling ammonia-free water until the 8. Report distillate shows no trace using nessler reagent— Report nitrogen, ammonia, dissolved (00608), CAUTION: deadly poison. and total (00610), concentrations as follows: less 6.3 Pipet a volume of well-mixed sample con­ than 1.0 mg/L, two decimals; 1.0 mg/L and taining less than 1*0 mg ammonia-nitrogen (250 above, two significant figures. mL max) into a 500-mL distillation flask, and ad­ just the volume to approx 250 mL with 9. Precision ammonia-free water (NOTE 1). 9.1 Precision for dissolved ammonia- NOTE 1. For watersuspended sediment mixtures, nitrogen for nine samples within the range rinse the pipet with ammonia-free water to remove of 0.10 to 2.0 mg/L may be expressed as adhering particles and combine with sample follows: 6.4 Add 12.5 mL borate buffer solution, and adjust the pH to 9.5 with 1M NaOH, if necessary. ST = 0.465X + 0.0001 6.5 Immediately distill at a rate of not more than 10 mL or less than 6 mL per min; collect the distillate in a 250-mL volumetric flask con­ where taining 25 mL boric acid solution. The tip of the ST = overall precision, milligrams per liter, delivery tube must be below the surface of the and boric acid solution in the receiving flask. X = concentration of ammonia-nitrogen, 6.6 Collect approx 200 mL of distillate, dilute milligrams per liter. to 250 mL with ammonia-free water, and mix. The correlation coefficient is 0.8140. 6.7 Pipet an aliquot of distillate containing 9.2 Precision for dissolved ammonia-nitro­ less than 0.1 mg ammonia-nitrogen (50.0 mL gen for four of the nine samples expressed in maximum) into a glass-stoppered, graduated terms of percent relative standard deviation is mixing cylinder, and adjust the volume to 50.0 as follows: mL with ammonia-free water. 6.8 Prepare a blank of ammonia-free water and Number of Mean Relative standard deviation a series of standards in glass-stoppered, graduated laboratories (mg/L) _____(percent)_____ mixing cylinders. Add 5 mL boric acid solution 11 0.104 73 to each, and adjust the volume of each to 50.0 mL. 4 .600 33 8 1.51 44 6.9 Add 1.0 mL nessler reagent—CAUTION: 7 2.04 63 deadly poison—to each blank, standard, and sampla Stopper and invert several times to mix 9.3 It is estimated that the percent relative thoroughly. standard deviation for total ammonia- nitrogen 6.10 Allow the solutions to stand at least 10 will be greater than that reported for dissolved min, but not more than 30 min. ammonia-nitrogen. 6.11 Determine the absorbance of each test sample and standard against the blank. Reference 7. Calculations 7.1 Determine milligrams of ammonia- Blaedel, W. J., and Meloche, V. W., 1963, Elementary quan­ nitrogen in each sample from a plot of absorb- titative analysis: theory and practice (2d ed.): New York, ances of standards. Harper and Row, 826 p. Nitrogen, ammonia, colorimetric, salicylate-hypochlorite, automated- segmented flow

Parameters and Codes: Nitrogen, ammonia, dissolved, 1-2522-85 (mg/L as N): 00608 Nitrogen, ammonia, total, 1-4522-85 (mg/L as N): 00610 Nitrogen, ammonia, total-in-bottom-material, I-6522-85 (mg/kg as N): 00611

1. Application 3.2 The samples are easily contaminated by 1.1 This method may be used to analyze sur­ ammonia in the laboratory atmosphere; face, domestic, and industrial water, brines, and therefore, sample handling and analysis should water-suspended sediment containing from 0.01 be performed where there is no possibility of to 1.5 mg/L of ammonia-nitrogen. Concentra­ ammonia contamination. tions greater than 1.5 mg/L need to be diluted. 1.2 This method may also be used to deter­ 4. Apparatus mine concentrations of ammonia-nitrogen in 4.1 Centrifuge. bottom material containing at least 0.2 mg/kg 4.2 Shaker, wrist-action. NHg-N. Prepared sample solutions containing 4.3 Technicon AutoAnalyzer II, consisting more than 1.5 mg/L NH3-N must first be of sampler, cartridge manifold, proportioning diluted. pump, heating bath, colorimeter, voltage 1.3 Sodium ion is a good replacement ion for stabilizer, recorder, and printer. ammonium in the slow-exchange positions of 4.4 With this equipment the following soil minerals (Jackson, 1958). The water-sus­ operating conditions have been found satisfac­ pended sediment is treated and preserved in the tory for the range from 0.01 to 1.5 mg/L field with mercury chloride and sodium chloride. ammonia-nitrogen: The resulting mixture, prior to analysis in the Absorption cell ——— 50 mm laboratory, is either centrifuged or decanted to Wavelength ————— 660 nm obtain a clear supernatant solution. Similarly, Cam —————————— 50/h (2/1) bottom material is treated with an acidified Heating-bath tempera­ sodium chloride solution and the resulting mix­ ture ———————— 37 °C ture centrifuged to obtain a clear supernatant solution for analysis. 5. Reagents 5.1 Ammonia standard solution I, 1.00 2. Summary of method mL = 0.50 mg NH3-N: Dissolve 1.9095 g Ammonia reacts with sodium salicylate, NH4C1, dried overnight over sulfuric acid, in sodium nitroprusside, and sodium hypochlorite, ammonia-free water and dilute to 1000 mL. in an alkaline medium, to form an intensely col­ Refrigerate. ored compound. The resulting color is directly 5.2 Ammonia standard solution II, 1.00 proportional to the concentration of ammonia mL = 0.0025 mg NH3-N: Dilute 5.0 mL am­ present. monia standard solution I to 1000 mL with ammonia-free water. Prepare fresh weekly and 3. Interferences refrigerate. 3.1 No substance found in natural waters 5.2.1 Ammonia working standards, bottom appears to interfere with this method. materials: Prepare an ammonia-free blank and 315 316 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS at least 250 mL each of a series of ammonia 5.8 Sodium chloride solution, 100 g/L: working standards by appropriate quantitative Dissolve 100 g NaCl in 800 mL ammonia-free dilution of ammonia standard solution II with water, mix thoroughly, and dilute to 1 L. Adjust acidified sodium chloride solution (5.8) as follows: the pH to 2.5 using concentrated HC1 (sp gr 1.19). 5.9 Sodium hydroxide solution, 5M: Add, Ammonia standard solution II Ammonia-nitrogen concentration (mL) (mg/L) with cooling and stirring, 200 g NaOH to approx­ imately 800 mL ammonia-free water. Cool and oo 00 2.0 .02 dilute to 1 L. 10 .10 5.10 Sodium hypochlorite solution: Dilute 50 25 .25 mL sodium hypochlorite solution (a commercial 50 .50 bleach solution containing 5.25-percent available 100 1.0 125 1.5 chlorine is satisfactory) to 500 mL with ammonia-free water. Add 1.0 mL Brij-35 solution. Prepare fresh weekly and refrigerate. Prepare fresh daily. 5.2.2 Ammonia working standards, water 5.11 Sodium salicylate-sodium nitroprusside and water suspended-sediment: Prepare an solution: Dissolve 150 g sodium salicylate and ammonia-free blank and at least 250 mL each 0.30 g sodium nitroprusside, (NagFelCN^NO- of a series of ammonia working standards by 2H2O), in approximately 600 mL ammonia-free dilution of ammonia standard solution II with water. Filter through Whatman 41 filter paper diluent solution (5.5) as follows: or equivalent, and dilute to 1 L. Add 1.0 mL Brij-35 solution and store in a light-resistant con­ Ammonia standard solution II Ammonia-nitrogen concentration tainer. (mL) (mg/L) 5.12 Sulfuric acid, concentrated (sp gr 1.84). 00 OO 5.13 Sulfuric acid, 2.5AT: Cautiously add 138 2.0 .02 10 .10 mL concentrated H2SO4 (sp gr 1.84) to approx­ 25 .25 imately 700 mL ammonia-free water. Cool and 50 .50 dilute to 1 L with ammonia-free water. 100 1.0 125 1.5 6. Procedure Prepare fresh weekly and refrigerate. 6.1 Proceed to paragraph 6.2 for waters or 5.3 Buffer stock solution, 71 g/L: Dissolve water-suspended sediments. For bottom 134 g Na2HPO4'7H2O in 800 mL ammonia-free materials begin with paragraph 6.1.1. water. Add 100 mL 5Af NaOH, dilute to 1 L 6.1.1 Weigh, to the nearest milligram, approx­ with ammonia-free water, and mix thoroughly. imately 5 g of sample prepared as directed in 5.4 Buffer working solution: Add, with stir­ either method P-0520 or PO810, and transfer to ring, 250 mL stock potassium sodium tartrate a 250-mL Erlenmeyer flask. solution to 200 mL stock buffer solution. Slow­ 6.1.2 Add 50 mL of the acidic sodium chloride ly, with stirring, add 120 mL 5M NaOH. Dilute solution (5.8) and shake on the wrist-action to 1 L with ammonia-free water, add 1 mL shaker for 30 min. Brij-35 solution, and mi* thoroughly. 6.1.3 Carefully transfer the entire sample, in­ 5.5 Diluent solution: Dissolve 52 mg mer­ cluding all sediment particles, to a centrifuge curic chloride (HgCl2) and 600 mg sodium tuba Centrifuge for 5 min; if the sample does not chloride (NaCl) in approximately 800 mL flocculate, add a drop of concentrated HC1 (sp gr ammonia-free water, mix thoroughly, and dilute 1.19) and recentrifuge. to 1 L with ammonia-free water. 6.1.4 Transfer the supernatant solution to a 5.6 Hydrochloric acid, concentrated (sp gr 100-mL volumetric flask, taking care not to 1.19). disturb the residue in the bottom of the cen­ 5.7 Potassium sodium tartrate solution, 149 trifuge tube. g/L: Dissolve 200 g NaKC4H4O6-4H2O in 6.1.5 Wash the sediment in the centrifuge tube approximately 600 mL ammonia-free water. with 20 mL acidic sodium chloride solution (5.8), Dilute to 1 L. recentrifuge, and transfer the clear wash solution METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 317 to the volumetric flask. Adjust to volume with least 5 min for the introduction of these acidic sodium chloride solution (5.8). Proceed to reagents, and then place the salicylate line into paragraph 6.2. its reagent container. If a precipitate forms 6.2 Set up the manifold (fig. 32). If the after the addition of the salicylate, the pH of laboratory air is contaminated with ammonia, the solution stream is too low; check for con­ the air must be passed through a scrubber con­ taminated reagents and (or) remake them, and taining 2.5M H2SO4 before the air enters the start again using the procedure outlined above. air-manifold tube. 6.5 Place a complete set of standards and a 6.3 Allow the colorimeter, recorder, and blank (NOTE 2) in the first positions of the first heating bath to warm for at least 30 min, or un­ sample tray, beginning with the most concen­ til the temperature of the heating bath reaches trated standard (NOTE 3). Place individual 37 °C. standards of differing concentrations in approx­ 6.4 Adjust the baseline to read zero scale imately every eighth position of the remainder divisions on the recorder with all reagents of this and subsequent sample trays. Fill the re­ (NOTE 1), but with either the acidic sodium mainder of each tray with unknown samples. chloride (paragraph 5.8, for bottom material NOTE 2. For analysis of bottom materials use analysis) or the diluent (paragraph 5.5, for water blank and working standards prepared in or water-suspended sediment analysis) in the paragraph 5.2.1. For analysis of waters and water- sample line. The solution remaining in the wash suspended-sediment mixtures, use blank and reservoir from previous determinations may working standards prepared in paragraph 5.2.2. have become contaminated; therefore, this NOTE 3. To avoid possible contamination of the reservoir should be emptied and rinsed, and sample cups, keep them sealed in their packages then refilled with fresh solution before until just prior to use. Rinse each sample cup proceeding. with sample prior to filling. NOTE 1. Place each reagent line except 6.6 Begin analysis. When the peak from the salicylate into its respective container; allow at most concentrated working standard appears on

To sampler 4 wash receptacle^ 0.90in Water 2.90mL/min Heating 0.035in Air bath 10-Turn 20-turn 5-turn ~ 0.42mL/min uiffluuu innran (nnoim awrtft lr 0.051 in Buffer ' i 4i i 1.00mL/min 37°C T O.OSSIn Sample 5 -Turn coil x. 0.42mL/min •0 Collorimeter x. x^_ O.OSOin Salicylate 0.32mL/min nitroprusside Sampler 4 6(>Gnm Waste \. 50/h 15- mm cell^ x^ 0.020 in Hypochlorlte 2/1 cam T 0.16mL/min •MMH TT - 0.060in Waste 7 "** 1.40mL/min 1 Recorder Proportioning pump

Figure 32.—Nitrogen, ammonia, salicylate-hypochlorite manifold 318 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS the recorder, adjust the STD CAL control un­ follows: less than 1.0 mg/L, two decimals; 1.0 til the flat portion of the peak reads full scale. mg/L and above, two significant figures. 8.2 Report nitrogen, ammonia, total in bot­ 7. Calculations tom material (00611), concentrations as follows: 7.1 Prepare an analytical curve by plotting less than 10 mg/kg, one decimal; 10 mg/kg and the height of each standard peak versus its above, two significant figures. respective ammonia-nitrogen concentration. 7.2 Compute the concentration of dissolved 9. Precision or total ammonia-nitrogen, in milligrams per 9.1 Single-operator precision for dissolved liter, in each sample by comparing its peak ammonia-nitrogen, as determined on synthetic, height to the analytical curve. Any baseline deionized water-matrix samples, expressed in drift that may occur must be taken into account terms of the percent relative standard devia­ when computing the height of a sample or tion, is as follows: standard peak. 7.3 Compute the concentration of ammonia- Number of Mean Relative standard devtation nitrogen in each bottom-material sample as determinations (mg/L) _____(percent)_____ follows: 77 0.20 13 77 1.25 3 77 2.00 2 NH3N (mg/kg) = wt of sample (g) 9.2 It is estimated that the percent relative standard deviation for total ammonia-nitrogen and for total ammonia-nitrogen in bottom where material will be greater than that reported for CN = NH3-N concentration in sample, dissolved ammonia-nitrogen. milligrams per liter. Reference 8. Report 8.1 Report nitrogen, ammonia, dissolved Jackson, M. L., 1958, Soil chemical analysis: Englewood (00608), and total (00610), concentrations as Cliffs, N.J., Prentice-Hall, p. 193. Nitrogen, ammonia, colorimetric, salicylate-hypochlorite, automated-discrete

Parameters and Codes: Nitrogen, ammonia, dissolved, 1-2521-85 (mg/L as N): 00608 Nitrogen, ammonia, total, 1-4521-85 (mg/L as N): 00610

1. Application through, quartz This method may be used to analyze water, cuvette wastewater, water-suspended sediment, and Reaction tempera­ brines containing 0.05 to 5.0 mg/L ammonia- ture ————— 37 °C nitrogen. Samples containing concentrations Sample volume - 0.150 mL with 0.100 mL greater than 5.0 mg/L need to be diluted. diluent (NOTE 1) Reagent volumes 0.5 mL buffer solution, 2. Summary of method 0.50 mL sodium Ammonia reacts with sodium salicylate, salicylate-sodium sodium nitroprusside, and sodium hypochlorite nitroprusside solution, to form an intensely colored compound in an 0.2 mL sodium hypo­ alkaline medium. The resulting color is direct­ chlorite solution, and ly proportional to the concentration of the am­ 0.80 mL demineralized monia present. water (NOTE 1)

3. Interferences NOTE 1. Sample-to-diluent ratio and reagent 3.1 A comparison study of the results ob­ volumes must be optimized for each individual tained by this method and those from the col­ instrument according to manufacturer's orimetric, salicylate-hypochlorite, automated- specifications. segmented flow method (methods 1-2522 and 4522) indicate the absence of interferences. 5. Reagents 3.2 Samples are easily contaminated by am­ 5.1 Ammonia standard solution /, 1.00 monia in the laboratory atmosphere; therefore, mL = 1.00 mg NH3-N: Dissolve 3.819 g sample handling and analysis should be per­ NH4C1, dried overnight over concentrated formed where there is no possibility of ammonia sulfuric acid (sp gr 1.84), in ammonia-free water contamination. and dilute to 1,000 mL. 5.2 Ammonia standard solution //, 1.00 4. Apparatus mL = 0.100 mg NH3-N: Dilute 100.0 mL am­ 4.1 Discrete chemical and analyzer system, monia standard solution I to 1,000 mL with American Monitor IQAS or equivalent. ammonia-free water. 4.2 With this equipment, the following oper­ 5.3 Ammonia working standards: Prepare a ating conditions have been found satisfactory blank and 1,000 mL each of a series of working for the range 0.01 to 5.00 mg/L. standards by dilution of ammonia standard Wavelength —— 620 nm solution II. Dissolve 52 mg mercuric chloride Absorption cell - 1 cm square, tempera­ and 600 mg sodium chloride in each working ture-controlled, flow- standard. For example:

319 320 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Standard solution II Ammonia-nitrogen concentration (ml) (mg/L) 6.3 Place standards, beginning with the lowest concentrations, in ascending order OO ooo (computer-calibration curve) in the first five 2.5 .25 5.0 .50 positions on the sample turntable. Place 10.0 1.00 samples and quality-control standards in the re­ 50.0 5.00 mainder of the sample turntable. 6.4 Begin analysis. The cathode-ray tube (CRT) will acknowledge the parameter and con­ 5.4 Buffer solution: Add, with stirring, 250 mL potassium sodium tartrate solution to 200 centration range listing each sample-cup mL sodium phosphate solution. Slowly, with number and corresponding concentrations cal­ stirring, add 120 mL 5Af NaOH. Dilute to 1 L culated from the working curve. During each run, the CRT display will provide a plot of with ammonia-free water. 5.5 Sodium hydroxide solution, 5M: Add, standards, samples, and list blank and slope cal­ with cooling and stirring, 200 g NaOH to ap- culations. Retain copy of all information ob­ prox 800 mL ammonia-free water. Cool and tained from the printer. dilute to 1 L. 5.6 Sodium hypochlorite solution: Dilute 6.0 7. Calculations mL sodium hypochlorite solution (a commercial Determine the concentration in milligrams bleach solution containing 5.25-percent per liter of dissolved or total ammonia-nitrogen in each sample from either the CRT display or available chlorine is satisfactory) to 100 mL with ammonia-free water. the printer output. 5.7 Sodium phosphate, diabasic solution, 71 g/L: Dissolve 71 g anhydrous Na2HPO4 in ap- 8. Report Report nitrogen, ammonia, dissolved (00608), prox 800 mL ammonia-free water. Add 100 mL 5M NaOH, dilute to 1 L with ammonia-free and total (00610), concentrations as follows: less water, and mix thoroughly. than 1.00 mg/L, two decimals; 1.0 mg/L and 5.8 Sodium potassium tartrate solution, 149 above, two significant figures. g/L: Dissolve 200 g NaKC4H4O6-4H2O in ap- prox 600 mL ammonia-free water. Dilute to 1 L. 9. Precision 5.9 Sodium scdicylate-sodium nitroprusside The precision expressed in terms of the stand­ solution: Dissolve 150 g sodium salicylate and ard deviation and percent relative standard 0.30 g sodium nitroprusside in approx 600 mL deviation for replicate analysis of reference ammonia-free water. Filter through Whatman materials by a single operator is as follows:

41 filter paper or equivalent, and dilute to 1 L. Relative standard Store in a light-resistant container. Mean Number of Standard deviation deviation (mo/L) replicates (mo/U (percent)

6. Procedure 0.014 39 0.002 14.3 .030 39 .003 10.0 6.1 Rinse all glassware with ammonia-free .186 30 .012 6.4 water before each use. .651 22 .010 1.5 6.2 Set up analyzer and computer-card 1.27 30 .020 1.6 2.48 22 .018 .7 assignments according to manufacturer's in­ 3.38 22 .093 2.8 structions. 4.99 30 .027 .5 Nitrogen, ammonia, colorimetric, indophenol, automated-segmented flow

Parameters and Codes: Nitrogen, ammonia, dissolved, 1-2523-85 (mg/L as N): 00608 Nitrogen, ammonia, total, 1-4523-85 (mg/L as N): 00610 Nitrogen, ammonia, totat-in-bottom-material, I-6523-85 (mg/kg as N): 00611

1. Application 3. Interferences 1.1 This method may be used to analyze sur­ A complexing reagent consisting of sodium face, domestic, and industrial water, and brines potassium tartrate and sodium citrate is added and water-suspended sediment containing from to remove interferences from several metal ions, 0.01 to 5.0 mg/L of ammonia-nitrogen. The including calcium, magnesium, and iron. The range may be extended if the nitroprusside is color development is pH dependent; therefore, omitted. samples whose pH values lie outside of the 1.2 This method may be used to determine range from 4 to 10 must be analyzed with stand­ concentrations of ammonia-nitrogen in bottom ards and a wash solution of approximately the material containing at least 0.2 mg/kg NH3-N. same pH. Aromatic amines may interfere. Prepared sample solutions containing more than 5.0 mg/L NH3-N must first be diluted. 4. Apparatus The range may be extended to 10.0 mg/L 4.1 Centrifuge. NH3-N if the nitroprusside is omitted. 4.2 Shaker, wrist-action. 1.3 Sodium ion is a good replacement ion for 4.3 Technicon AutoAnalyzer //, consisting ammonium in the slow-exchange positions of of sampler, cartridge manifold, proportioning soil minerals (Jackson, 1958). Water-suspended pump, heating bath, colorimeter, voltage stabil­ sediment is treated and preserved in the field izer, recorder, and printer. with mercury chloride and sodium chloride. The 4.4 With this equipment the following oper­ resulting mixture, prior to analysis in the labor­ ating conditions have been found satisfactory atory, is either centrifuged or decanted to for the range from 0.01 to 5.0 mg/L ammonia- obtain clear supernatant solution. Similarly, nitrogen. bottom material is treated with an acidified Absorption cell ——— 15 mm sodium chloride solution, and the resulting mix­ Wavelength ————— 630 nm ture centrifuged to obtain a clear supernatant Cam ——r-———————— 60/h (6/1) solution for analysis. Heating-bath tempera­ ture ———————— 50 °C 2. Summary of method Ammonia reacts with hypochlori te and alkaline 5. Reagents phenol to form an intensely colored indophenol 5.1 Alkaline phenol solution: Mix 89 mL li­ compound, the absorbance of which is directly quid phenol (approx 90 percent) in 50 mL proportional to the ammonia concentration. So­ ammonia-free water. Cautiously add, while cool­ dium nitroprusside may be added to improve the ing, in small increments with agitation, 180 mL sensitivity of this determination (Bolleter and 5M NaOH. Dilute to 1 L with ammonia-free othere, 1961; O'Brien and More, 1962; letlow and water (NOTE 1). Keep refrigerated in an amber Wilson, 1964; Van Slyke and Hiller, 1933). bottle. 321 322 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Ammonia standard solution I, 1.00 water. Cool and dilute to 1 L. Store in a plastic mL = 1.00 mg NH3-N: Dissolve 3.819 g container. NH4C1, dried overnight over sulfuric acid, in 5.11 Sodium hypochlorite stock solution: ammonia-free water and dilute to 1,000 mL. Clorox or any other good commercial household Refrigerate. bleach having approx 5-percent available 5.3 Ammonia standard solution II, 1.00 chlorine. mL = 0.025 mg NH3-N: Dilute 25.0 mL am­ 5.12 Sodium hypochlorite working solution: monia standard solution I to 1,000 mL with Dilute 200 mL of stock sodium hypochlorite to diluent solution (paragraph 5.6). Prepare fresh 1 L with ammonia-free water. weekly and refrigerate. 5.13 Sodium nitroprusside solution, 0.44 g/L: 5.4 Ammonia working standards: Prepare a Dissolve 0.5 g Na2Fe(CN)5NO-2H2O in am­ blank and 250 mL each of a series of ammonia monia-free water and dilute to 1 L. working standards by appropriate quantitative 5.14 Sulfuric acid, concentrated (sp gr 1.84). dilution of ammonia standard solution II with 5.15 Sulfuric acid, 2.5M- Cautiously, add 138 diluent solution (paragraph 5.6) as follows mL concentrated (sp gr 1.84) to 500 mL am­ (NOTE 1): monia-free water, cool, and dilute to 1 L.

Ammonia standard solution II Ammonia-nitrogen concentration (mL) (mg/L) 6. Procedure 6.1 Proceed to paragraph 6.2 for waters or 0.0 0.0 10 1.0 water-suspended sediments. For bottom mate­ 20 2.0 rials begin with paragraph 6.1.1. 30 3.0 6.1.1 Weigh, to the nearest milligram, approx 40 4.0 50 5.0 5 g of sample, prepared as directed in either method P-0520 or P-0810, and transfer to a Prepare fresh weekly and refrigerate. 250-mL Erlenmeyer flask. NOTE 1. If ammonia-nitrogen in bottom mate­ 6.1.2 Add 50 mL NaCl solution and shake on rial is being determined, the working standards the wrist-action shaker for 30 min. are diluted with sodium chloride solution 6.1.3 Carefully transfer the entire sample, in­ (paragraph 5.9). cluding all sediment particles, to a centrifuge 5.5 Brij-35 solution: 30-percent aqueous solu­ tube. Centrifuge for 5 min; if the sample does tion (Baker Cat. No. C706 or equivalent). not flocculate, add a drop of concentrated HC1 5.6 Diluent solution: Dissolve 52 mg mer­ (sp gr 1.19) and recentrifuge. curic chloride and 600 mg sodium chloride in 6.1.4 Transfer the supernatant solution to a 800 mL ammonia-free water, mix thoroughly, 100-mL volumetric flask, taking care not to and dilute to 1 L with ammonia-free water. disturb the residue in the bottom of the cen­ 5.7 Hydrochloric acid, concentrated (sp gr trifuge tube. 1.19). 6.1.5 Wash the sediment in the centrifuge 5.8 Potassium sodium tartrate-sodium tube with 20 mL NaCl solution, recentrifuge, citrate solution: Dissolve 33 g KNaC4H4O6- and transfer the dear wash solution to the volu­ 4H2O and 24 g sodium citrate in 950 mL metric flask. Adjust to volume with NaCl solu­ ammonia-free water. Adjust the pH of this solu­ tion. Proceed to paragraph 6.2. tion to 5.0 with concentrated H2SO4 (sp gr 1.84) 6.2 Set up manifold (fig. 33). If the labor­ and dilute to 1L with ammonia-free water. Add atory air is contaminated with ammonia, the air 0.5 mL Brij-35 solution. must be passed through a scrubber containing 5.9 Sodium chloride solution, 100 g/L: 2.5M H2SO4 before the air enters the air- Dissolve 100 g NaCl in 800 mL ammonia-free manifold tube. water, mix thoroughly, and dilute to 1 L. Ad­ 6.3 Allow the colorimeter, recorder, and heat­ just the pH to 2.5 using concentrated HC1 (sp ing bath to warm for at least 30 min, or until the gr 1.19). temperature of the heating bath reaches 50 °C. 5.10 Sodium hydroxide solution, 5M: Cau­ 6.4 Adjust the baseline to read zero scale tiously, dissolve 200 g NaOH in ammonia-free divisions on the recorder with all reagents, METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 323

0,030 in Air 20-turn coil 20-turn coil 0.32 mL/min 0.045in0.04 Tartrate-citrate 0.80Off mL/min

0.035in Sample 0.42 mL/min

0.035in Alkaline phenol Heating Sampler 4 0.42 mL/min bath 60/h 50°C 0.030in0.03 Hypochlorite 6/lcam 157 -B273-32 0.32 mL/min

0.035 in Nitroprusside Colorimeter 0.42 mL/min To sampler 4 630 nm 0.073 in Water 15-mm cell wash receptacle .065in Waste 1.60 mL/min Recorder Proportioning pump Figure 33.—MUuyen, dinmuula, InUupMenul manifold but with ammonia-free water in the sample line. the height of each standard peak versus its 6.5 Place a complete set of standards and a respective ammonia-nitrogen concentration. blank in the first positions of the first sample 7.2 Compute the concentration of dissolved tray, beginning with the most concentrated or total ammonia-nitrogen, in milligrams per standard (NOTE 2). Place individual standards liter, in each sample by comparing its peak of differing concentrations in approximately height to the analytical curve. Any baseline every eighth position of the remainder of this drift that may occur must be taken into account and subsequent sample trays. Fill remainder of when computing the height of a sample or each tray with unknown samples. standard peak. NOTE 2. To avoid possible contamination of the 7.3 Compute ammonia-nitrogen concentra­ sample cups, keep them sealed in their packages tions in each bottom material sample as follows: until just prior to use. Rinse each sample cup with sample prior to filling. 6*6 Begin analysis. When the peak from the _ CN X 100 most concentrated working standard appears NH3-N (mg/kg) on the recorder, adjust the STD CAL control wt of sample (g) until the flat portion of the peak reads full scale. where 7. Calculations CN = NH3-N concentration in sample, milli­ 7.1 Prepare an analytical curve by plotting grams per liter. 324 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 8. Report Number of Mean Relative standard deviation laboratories (mg/L) _____(percent)_____ 8.1 Report nitrogen, ammonia, dissolved (00608), and total (00610), concentrations as 8 0.126 17 21 .665 13 follows: less than 1.0 mg/L, two decimals; 1.0 20 1.20 17 mg/L and above, two significant figures. 23 3.25 12 8.2 Report nitrogen, ammonia, total-in- bottom-material (00611), concentrations as 9.3 It is estimated that the percent relative follows: less than 10 mg/kg, one decimal; 10 standard deviation for total ammonia-nitrogen nag/kg and above, two significant figures. and for total ammonia-nitrogen in bottom material will be greater than that reported for 9. Precision dissolved ammonia-nitrogen. 9.1 Precision for dissolved ammonia-nitro­ gen for nine samples within the range of 0.126 to 3.25 mg/L may be expressed as follows: References

ST = 0.098X + 0.079 Bolleter, W. T.f Bushman, C. J., and Tidwell, P. W., 1961, Spectrophotometric determination of ammonia as in- where dophenol: Analytical Chemistry, v. 33, p. 592-3. ST = overall precision, milligrams per liter, Jackson, M. L., 1958, Soil chemical analysis: Englewood Cliffs, N.J., Prentice-Hall, p. 193. and O'Brien, J. E., and Fiore, J., 1962, Ammonia determination X = concentration of ammonia-nitrogen, by automatic analysis: Wastes Engineering, v. 33, milligrams per liter. p. 352. The correlation coefficient is 0.9085. Tetlow, J. A., and Wilson, A. L.., 1964, An absorptiometric 9.2 Precision for dissolved ammonia-nitro­ method for determining ammonia in boiler-feed water: Analyst, v. 89, p. 453-65. gen for four of the nine samples expressed in Van Slyke, D. D., and Miller, A. J., 1933, Determination of terms of percent relative standard deviation is ammonia in blood: Biological Chemistry Journal, v. 102, as follows: p. 499. Nitrogen, ammonia, electronnetric, ion-selective electrode

Parameters and Codes: Nitrogen, ammonia, dissolved, 1-1524-85 (mg/L as N): 00608 Nitrogen, ammonia, total, I-3524-85 (mg/L as N): 00610

1. Application 4. Apparatus This method may be used to analyze water, 4.1 Ammonia electrode, Orion Model No. brines, and water-suspended sediment contain­ 95-10 or equivalent. ing at least 0.10 mg/L ammonia-nitrogen. Sam­ 4.2 pH/millivolt meter, with expanded scale. ples containing less than 0.10 mg/L need to be 4.3 Stirrer, magnetic, battery-operated, with analyzed by the single standard addition tech­ Teflon-coated stirring bar. nique (paragraph 6.6). 5. Reagents 2. Summary of method 5.1 Ammonia standard solution /, 1.00 Ammonia is determined potentiometrically in mL = 1.00 mg NH3-N: Dissolve 3.819 g am­ an alkaline medium by using an ammonia gas- monium chloride (NH4C1), dried overnight over detecting electrode. The internal solution of the sulfuric acid, in ammonia-free water and dilute electrode is separated from the sample solution to 1,000 mL. by a gas-permeable membrane. Dissolved am­ 5.2 Ammonia standard solution //, 1.00 monia in the sample diffuses through the mem­ mL — 0.010 mg N: Dilute 10.0 mL of ammonia brane until the partial pressure of ammonia is standard solution I to 1,000 mL with ammonia- the same on both sides. The change in partial free water. Prepare fresh daily. pressure is proportional to the ammonia concen­ 5.3 Ammonia working standards: Prepare a tration and is measured as a potential with an series of three standard solutions containing internal chloride-sensing reference electrode and 0.1, 1.0, and 5.0 mg/L NH3-N by appropriate a glass electrode. dilution of either ammonia standard solution I or II with ammonia-free water. 3. Interferences 5.4 Sodium hydroxide solution, lOAf. 3.1 Color and turbidity do not affect the Dissolve with caution 400 g NaOH in ammonia- measurements. Significant quantities of inor­ free water and dilute to 1 L. ganic cations and anions cannot penetrate the nonwettable, gas-permeable membrane and do 6. Procedure not interfere directly. However, as the salinity 6.1 Rinse all glassware with ammonia-free of the sample increases, there is an increase in water before beginning this determination. the observed ammonia concentration. Samples 6.2 Adjust the pH/millivolt meter according containing dissolved substances at a total con­ to the manufacturer's instructions. centration greater than 1M should be analyzed 6.3 Pipet 50.0 mL of each ammonia chloride by standard addition or, if the ammonia concen­ working standard (0.1, 1.0, and 5.0 mg/L tration is sufficiently high, be analyzed after ap­ NH3-N, respectively) into 100-mL beakers. propriate dilution. 6.4 Pipet 50.0 mL of well-mixed sample in­ 3.2 Certain gases do present a potential in­ to a 100-mL beaker. terference; however, common gases such as 6.5 Place each standard and sample con­ CO2, HCN, SO2, and C12 do not interfere (Orion secutively on a magnetic stirrer (NOTE 1), im­ Research Inc., 1971). merse the electrode, and then add 0.5 mL 10M 325 326 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS NaOH solution. Start the stirrer and record the 9. Precision potential (mV) reading after it has stabilized (2 9.1 Precision for dissolved ammonia-nitro­ to 5 min). Rinse the electrode thoroughly with gen for seven samples within the range of 0.339 distilled water between samples and blot with to 3.48 mg/L may be expressed as follows: a damp tissue. " NOTE 1. Insulate the top of the stirrer with an asbestos sheet and an air space to avoid rais­ ST = Q.UQX+ 0.083 ing the temperature of the solution. 6.6 If the millivolt reading from the analyt­ where ical curve (paragraph 7) indicates a concentra­ ST = overall precision, milligrams per liter, tion of less than 0.10 mg/L, determine NH3-N and in the sample by single standard addition X = concentration of ammonia-nitrogen, (paragraph 6.7). milligrams per liter. 6.7 Add 0.5 mL ammonia chloride standard The correlation coefficient is 0.8331. solution II to the sample (paragraph 6.5), 9.2 Precision for dissolved ammonia-nitro­ equivalent to an increase in concentration of gen for four of the seven samples expressed in 0.10 mg/L NH3-N, and record the new poten­ terms of percent relative standard deviation is tial. Approx 5 min is required for the potential as follows: to stabilize.

Number of Mean Relative standard deviation 7. Calculations laboratories _____(percent)_____ Construct an analytical curve of potential 7 0.339 45 (mV) versus concentration of standards on 4 .620 13 semilog paper, with concentrations plotted on 7 1.01 29 the logarithmic axis. Determine the milligrams 3.48 17 per liter ammonia-nitrogen in each sample from the analytical curve. When standard addition 9.3 It is estimated that the percent relative is used to determine NH3-N (paragraph 6.7), standard deviation for total ammonia-nitrogen subtract 0.10 mg/L NH3-N from the concentra­ will be greater than that reported for dissolved tion obtained from the analytical curve. ammonia-nitrogen. 8. Report Report nitrogen, ammonia, dissolved (00608), Reference and total (00610), concentrations as follows: less than 1.0 mg/L, two decimals; 1.0 mg/L and Orion Research, Inc., 1971, Instruction manual, ammonia above, two significant figures. ammonia electrode, Model 95-10: Cambridge, Mass. Nitrogen, ammonia plus organic, colorimetric, block digestor-salicylate-hypochlorite, automated-segmented flow

Parameters and Codes: Nitrogen, ammonia plus organic, dissolved, 1-2552-85 (mg/L as N): 00623 Nitrogen, ammonia plus organic, total, 1-4552-85 (mg/L as N): 00625 Nitrogen, ammonia plus organic, suspended-total, 1-7552-85 (mg/L as N): 00624 Nitrogen, ammonia plus organic, total-in-bottom-material, dry wt, 1-6552-85 (mg/kg as N): 00626

1. Application (methods 1-1550 and 1-2551, respectively) in­ 1.1 This method may be used to analyze water dicated the absence of interferences. and water-suspended sediment containing 0.2 3.2 The samples are easily contaminated by to 10 mg/L total ammonia plus organic nitro­ ammonia in the laboratory atmosphere. The gen. Samples containing concentrations greater digestion process should be performed in a fume than 10 mg/L need to be diluted. hood that is operating properly and that is 1.2 Suspended total ammonia plus organic located in an ammonia-free area of the labora­ nitrogen is calculated by subtracting dissolved tory. Other laboratory procedures may be per­ ammonia plus organic nitrogen from total am­ formed outside or near this hood only if there monia plus organic nitrogen. is no possibility of ammonia contamination. 1.3 This method may be used to analyze samples of bottom material containing at least 4. Apparatus 10 mg/kg total ammonia plus organic nitrogen. 4.1 Technicon block digestor, Model BD-40 Concentration ranges for determining 10 to 120 with 75-mL digestion tubes or equivalent. mg/kg and 80 to 400 mg/kg of nitrogen are used. 4.2 With this equipment, the following oper­ ating conditions have been found satisfactory: 2. Summary of method Modeswitch ————— Automatic Organic nitrogen compounds are reduced to Low-temperature regu­ the ammonium ion by digestion with sulfuric lator ———————— 160°C acid in the presence of mercuric sulfate, which High-temperature regu­ acts as a catalyst, and potassium sulfate. The lator ———————— 370°C ammonium ion produced by this digestion, as Low-temperature timer 1.5 h well as the ammonium ion originally present, is Total cycle time ——— 3.5 h determined by reaction with sodium salicylate, 4.3 Technicon AutoAnalyzer II, consisting sodium nitroprusside, and sodium hypochlorite of sampler, cartridge manifold, proportioning in an alkaline medium. The resulting color is pump, heating bath, colorimeter, voltage stabil­ directly proportional to the concentration of am­ izer, recorder, and printer. monia present. 4.4 With this equipment, the following operating conditions have been found satisfac­ 3. Interferences tory (NOTE 1): 3.1 A comparison study of results obtained Absorption cell ——— 15 mm by this method with those from the colori­ Wavelength ————— 660 nm metric, digestion-distillation-nesslerization Cam —————————— 60/h (6/1) method, and the colorimetric, digestion- Water-bath tempera­ distillation-indophenol, automated method ture ————————— 37 °C 327 328 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS NOTE 1. Two concentration ranges—0.2 to 3 5.12 Sulfuric acid, 3.6M Cautiously, add 200 mg/L and 2 to 10 mg/L N—are obtained by mL concentrated H2SO4 (sp gr 1.84) to approx using different STD CAL settings. 700 mL ammonia-free water. Cool and dilute to 1 L with ammonia-free water. 5. Reagents 5.13 Sulfuric acid-mercuric sulfate-potassium 5.1 Ammonia standard solution I, 1.00 mL = sulfate solution: Dissolve 267 g K2SO4 in ap­ 1.00 mg NH3-N: Dissolve 3.819 g NH4C1, dried prox 1,300 mL ammonia-free water. Cautious­ overnight over sulfuric acid, in ammonia-free ly, add 400 mL concentrated H2SO4 (sp gr 1.84) water and dilute to 1,000 mL. and 50 mL mercuric sulfate solution* Cool and 5.2 Ammonia standard solution II, 1.00 dilute to 2 L with ammonia-free water. mL = 0.010 mg NH3-N: Dilute 10.0 mL am­ monia standard solution I to 1,000 mL with 6. Procedure ammonia-free water. Prepare fresh daily. 6.1 Rinse all glassware with ammonia-free 5.3 Buffer stock solution, 71 g/L: Dissolve 71 water before each use. g anhydrous Na2HPO4 in approx 800 mL 6.2 Follow instructions in paragraph 6.2.1 ammonia-free water. Add 100 mL 5M NaOH, for waters or water-suspended sediments and dilute to 1 L with ammonia-free water, and mix in paragraph 6.2.2 for bottom materials. thoroughly. 6.2.1 Pipet a volume (20.0 mL max) of well- 5.4 Buffer working solution: Add, with stir­ mixed sample (NOTE 2) containing less than 0.2 ring, 250 mL stock potassium sodium tartrate mg ammonia plus organic nitrogen (as N) into solution to 200 mL stock buffer solution. Slow­ a digestion tube and adjust the volume to 20 ly, with stirring, add 120 mL 5M NaOH. Dilute mL with ammonia-free water. to 1L with ammonia-free water, add 1 mL Brij-35 NOTE 2. For water-suspended sediment, rinse solution, and mix thoroughly. the pipet with a small amount of ammonia-free 5.5 Mercuric sulfate solution, 11 g/100 mL: water to remove adhering particles, and com­ Dissolve 8 g led HgO in 50 mL 3.6M H2SO4 and bine with sample. dilute to 100 mL with ammonia-free water. 6.2.2 Weigh, to the nearest milligram, an 5.6 Potassium sodium tartrate solution, 149 amount of wet sample (500 mg max) containing g/L: Dissolve 200 g NaKC4H4O6-4H2O in apprax less than 0.2 mg total ammonia plus organic 600 mL ammonia-free water. Dilute to 1 L. nitrogen. Transfer the weighed sample to a 5.7 Sodium hydroxide solution, 5M: Add, digestion tube, rinsing the weighing container with cooling and stirring, 200 g NaOH to approx with ammonia-free water as needed. Add addi­ 800 mL ammonia-free water. Cool and dilute to tional ammonia-free water as necessary to bring 1L. the liquid volume in the digestion tube to ap­ 5.8 Sodium hypochhrite solution: Dilute 6.0 proximately 20 mL. mL sodium hypochlorite solution (a commercial 6.3 Prepare an ammonia-free water blank bleach solution containing 5.25-percent available and at least five standards containing either chlorine is satisfactory) to 100 mL with from 0.004 to 0.06 mg or from 0.04 to 0.20 mg ammonia-free water. Add 0.1 mL Brij-35 solution. ammonia-nitrogen, depending upon use of 0,2- Prepare fresh daily. to 3-mg/L or 2- to 10-mg/L concentration range 5.9 Sodium salicylate-sodium nitroprusside of interest (NOTE 3). The standards and blank solution: Dissolve 150 g sodium salicylate and must also undergo the digestion process. 0.30 g sodium nitroprusside, (Na2Fe(CN)5NO- NOTE 3. The blank and standards must con­ 2H2O), in approx 600 mL ammonia-free water. tain mercuric chloride fortified with sodium Filter through Whatman 41 filter paper or chloride. For example, if 250 mL is prepared, equivalent, and dilute to 1 L. Add 1.0 mL Brij-35 dissolve 13 mg HgCl2 and 150 mg NaCl in each solution and store in a light-resistant container. standard. 5.10 Sulfuric acid, concentrated (sp gr 1.84). 6.4 Add 4.0 mL sulfuric acid-mercuric 5.11 Sulfuric acid, 0.20M- Cautiously, add 11 sulfate-potassium sulfate solution and two boil­ mL concentrated H2SO4 (sp gr 1.84) to ing chips. CAUTION: Hazardous. Mix well ammonia-free water and dilute to 1 L. before placing in digester (NOTES 4 and 5). METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 329 NOTE 4. Protective eyeglasses and clothing are range, this dilution must be made with 0.20M mandatory for this procedure because sulfuric H2S04. acid and high-temperature solutions are very NOTE 6. The precipitation of salts is minimized hazardous. by this procedure. A vortex mixer is useful for NOTE 5. Teflon boiling chips, available from agitating the water-acid mixture. Cole-Parmer Instrument Co., are preferable. NOTE 7. Allow any precipitate that has formed Before use they should be soaked in dilute HC1 or any boiling chip flakes to settle before fill­ (approx 6M), rinsed several times in ammonia- ing the sample cups as described in paragraph free water, and dried at 180 °C. In order to avoid 6.10. contamination by laboratory fumes, store them 6.7 Set up manifold (fig. 34). If the in a tightly stoppered container in an ammonia- laboratory air is contaminated with ammonia, free area of the laboratory. the air must be passed through a scrubber con­ 6.5 Digest under a hood for 3Y2 h using the taining 2.5M H2SO4 before the air enters the listed conditions. It is imperative that the air-manifold tube. heating block cool to 150°C before subsequent 6.8 Allow the colorimeter, recorder, and batches of samples are placed in the digester or heating bath to warm for at least 30 min. extreme spattering will occur. 6.9 Adjust the baseline to read zero scale 6.6 Cautiously remove tubes from the divisions on the recorder with all reagents, but digestor and allow to cool for approx 15 min in with 0.20M H2SO4 in the sample line. The solu­ a hood. Quickly add approx 50 mL ammonia- tion remaining in the wash reservoir from free water to each tube with vigorous agitation previous analyses may have become contami­ and extreme caution (NOTE 6). Allow to cool nated; therefore, this reservoir should be emp­ briefly before making the final dilution to the tied and rinsed, and filled with fresh wash calibration mark. Stopper the tubes and invert solution before proceeding. Place each reagent several times until well mixed (NOTE 7). If a line except salicylate into its respective con­ portion of this solution must be diluted to re­ tainer; allow at least 5 min for the introduction main within the designated concentration of these reagents, and then place the salicylate

To sampler 4 wash receptacle 0.056 in H2S04 0,20111 1.20mL/min 0.030 in Air ID-turn 20-turn 5- turn 0.32mL/min coil coil coil 0.056 in Buffer 37°C 1.20mL/min 0.020 in Sample 5-turn coil 0.16mL/min 0.030 in Salicylate Colorimeter 0.32ml/min nitroprusside Sampler 4 0.020 in Hypochlorite 607 h 0.16 mL/min 6/1 cam 0.065 in Waste 1.60 mL/min Recorder Proportioning pump

Figure 34.—Nitrogen, ammonia plus organic, salicylate-hypochlorite manifold 330 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS line into its reagent container. If a precipitate 7.4 Determine the concentration of total am­ forms after the addition of the salicylate, the pH monia plus organic nitrogen in bottom material of the solution stream is too low. as follows: 6.10 Place a complete set of standards and a blank in the first positions of the first sample Nitrogen, ammonia plus organic (mg/kg) = tray, beginning with the most concentrated standard (NOTE 8). Place individual standards mg NH3-N in sample X 1000 of differing concentrations in approximately ample dry wt (g) every eighth position of the remainder of this and subsequent sample trays. Fill remainder of 8. Report each tray with unknown samples. 8.1 Report nitrogen, ammonia plus organic, NOTE 8. To avoid possible contamination of the dissolved (00623), total (00625), suspended-total sample cups, keep them sealed in their packages (00624), concentrations as follows: 0.2 to 1.0 until just prior to use. Rinse each sample cup mg/L, one decimal; 1.0 mg/L and above, two with sample prior to filling. significant figures. 6.11 Begin analysis. When the peak from the 8.2 Report nitrogen, ammonia plus organic, most concentrated working standard appears total-in-bottom-material (00626), in milligrams on the recorder, adjust the STD CAL control per kilogram of dry-weight sample, concentra­ until the flat portion of the peak reads full scale. tions as follows: less than 1,000 mg/kg, nearest 10 mg/kg; 1,000 mg/kg and above, two signifi­ 7. Calculations cant figures. 7.1 Determine the milligrams of ammonia- nitrogen in each sample from a plot of peak 9. Precision heights of standards. Any baseline drift that 9.1 The standard deviation for dissolved am­ may occur must be taken into account when monia plus organic nitrogen within the range computing the height of a sample or standard of 0.68 to 1.41 mg/L for seven samples was peak. Likewise, the amount of NH3-N present found to be independent of concentration. The from the addition of H2SO4, as indicated by the 95-percent confidence interval for the average concentration of NH3-N in the blank, must be standard deviation of 0.577 mg/L ranged from subtracted from the total milligrams of NH3-N 0.486 to 0.750 mg/L. in each sample. 9.2 Precision for dissolved ammonia plus 7.2 Determine the concentration of dis­ organic nitrogen for three of the seven samples solved or total ammonia plus organic nitrogen expressed in terms of the percent relative stand­ as follows: ard deviation is as follows:

Nitrogen, ammonia plus organic (mg/L) = Number of Mean Relative standard deviation laboratories (mg/L) _____(percent)_____ 1,000 8 0.675 63 X mg NH3-N in sample 8 1.14 54 mL sample 8 1.41 54 9.3 It is estimated that the percent relative 7.3 To determine the concentration of standard deviation for total and suspended suspended total ammonia plus organic nitrogen, total ammonia plus organic nitrogen and for subtract dissolved ammonia-plus-organic total ammonia plus organic nitrogen in bottom nitrogen concentration from total ammonia- material will be greater than that reported for plus-organic nitrogen concentration. dissolved ammonia plus organic nitrogen. Nitrogen, ammonia plus organic, colorimetric, block digestor-salicylate-hypochlorite, automated-discrete

Parameters and Codes: Nitrogen, ammonia plus organic, dissolved, 1-2558-85 (mg/L as N): 00623 Nitrogen, ammonia plus organic, total, 1-4558-85 (mg/L as N): 00625 Nitrogen, ammonia plus organic, suspended total, 1-7558-85 (mg/L as N): 00624

1. Application performed outside or near this hood only if 1.1 This method may be used to analyze there is no possibility of ammonia con­ water and water-suspended sediment contain­ tamination. ing from 0.2 to 5.0 mg/L ammonia plus organic nitrogen. Samples containing concentrations 4. Apparatus greater than 5.0 mg/L need to be diluted. 4.1 Block digester, Technicon Model BD-40 1.2 Suspended total ammonia plus organic with 75-mL digestion tubes or equivalent. nitrogen is calculated by subtracting dissolved 4.2 With this equipment, the following oper­ ammonia plus organic nitrogen from total am­ ating conditions have been found satisfactory: monia plus organic nitrogen. Modeswitch —— Automatic Low-temperature 2. Summary of method regulator — 160 °C Organic nitrogen compounds are reduced to High-tempera­ the ammonium ion by digestion with sulfuric ture regulator 370 °C acid in the presence of mercuric sulfate, which Low-temperature acts as a catalyst, and potassium sulfate. The timer ———— 1.5 h ammonium ion produced by this digestion, as Total cycle time 3.5 h well as the ammonium ion originally present, is 4.3 Discrete analyzer system, American determined by reaction with sodium salicylate, Monitor IQAS or equivalent. sodium nitroprusside, and sodium hypochlorite 4.4 With this equipment, the following oper­ in an alkaline medium. The resulting color is ating conditions have been found satisfactory: directly proportional to the concentration of am­ Wavelength —— 620 nm monia present. Absorption cell 1 cm square, tempera­ ture-controlled, flow- 3. Interferences through quartz 3.1 A comparision study of results obtained cuvette by this method with those from the colori­ Reaction temper­ metric, block-digestor salicylate-hypochlorite, ature —————— 40 °C automated-segmented-flow method (method Sample volume 0.375 mL with 0.075 1-2552) indicates the absence of interferences. mL diluent 3.2 The samples are easily contaminated by Reagent volumes 1.0 mL buffer solu­ ammonia in the laboratory atmosphere. The tion, 0.45 mL sodium digestion process should be performed in a fume salicylate-sodium hood that is operating properly and that is nitroprusside solution, located in an ammonia-free area of the labora­ and 0.25 mL sodium tory. Other laboratory procedures may be hypochlorite solution 331 332 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS NOTE 1. Sample-to-diluent ratio and reagent 5.9 Sodium potassium tartrate solution, 149 volumes must be optimized for each instrument g/L: Dissolve 200 g NaKC4H4O6-4H2O in ap­ according to manufacturer's specifications. prox 600 mL ammonia-free water. Dilute to 1 L. 5.10 Sodium salicylate-sodium nitroprusside 5. Reagents solution: Dissolve 150 g sodium salicylate and 5.1 Ammonia standard solution I, 1.00 0.50 g sodium nitroprusside in approx 600 mL mL = 1.00 mg NH3-N: Dissolve 3.819 g ammonia-free water. Dilute to 1 L with am­ NH4C1, dried overnight over sulfuric acid, in monia-free water, and store in a light-resistant ammonia-free water and dilute to 1,000 mL. container. 5.2 Ammonia standard solution II, 1.00 5.11 Sulfuric acid, concentrated (sp gr 1.84). mL = 0.10 mg NH3-N: Dilute 100.0 mL am­ 5.12 Sulfuric acid, 0.20 M: Cautiously, add 11 monia standard solution I to 1,000 mL with mL concentrated H2SO4 (sp gr 1.84) to am­ ammonia-free water. monia-free water and dilute to 1 L with 5.3 Ammonia working standards: Prepare a ammonia-free water. blank and 1,000 mL each of a series of working 5.13 Sulfuric acid, 3.6 M: Cautiously, add standards by dilution of ammonia standard 200 mL concentrated H2SO4 (sp gr 1.84) to ap­ solution II. Dissolve 52 mg mercuric chloride prox 700 mL ammonia-free water. Cool and and 600 mg sodium chloride in each working dilute to 1 L with ammonia-free water. standard. 5.14 Sulfuric acid-mercuric sulfate-potassium sulfate solution: Dissolve 267 g K2804 in ap­ 'Standard solution M Nitrogen concentration prox 1,300 mL ammonia-free water. Cautious­ (mL) (mo/L) ly, add 400 mL concentrated H2SO4 (sp gr 1.84) 16 O2 and 50 mL mercuric sulfate solution. Cool and 5.0 0.5 dilute to 2 L with ammonia-free water. 10 1 30 3 50 5 6. Procedure Rinse all glassware with ammonia-free water before each use. 5.4 Buffer solution: Add, with stirring, 250 6.1 Pipet a volume (20.0 mL max) of well- mL potassium sodium tartrate solution to 200 mixed sample containing less than 0.1 mg am­ mL sodium phosphate solution. Slowly, with monia plus organic nitrogen (as N) into a diges­ stirring, add 120 mL 5 M NaOH. Dilute to 1 L tion tube and adjust the volume to 20 mL with with ammonia-free water. ammonia-free water. For water-suspended sedi­ 5.5 Mercuric sulfate solution, 11 g/100 mL: ment mixtures, rinse the pipet with a small Dissolve 40 g red HgO in 250 mL 3.6 M amount of ammonia-free water to remove adher­ H28O4 and dilute to 500 mL with ammonia-free ing particles, and combine with sample. water. 6.2 Prepare a blank and four standards in a 5.6 Sodium hydroxide solution, 5 M: Add, similar manner. The blank and standards must with cooling and stirring, 200 g NaOH to ap- also undergo the digestion process. prox 800 mL ammonia-free water. Cool and 6.3 Add 4.0 mL sulfuric acid-mercuric sul­ dilute to 1 L. fate-potassium sulfate solution and two boiling 5.7 Sodium hypochlorite solution: Dilute 6.0 chips. CAUTION: Hazardous. Mix well before mL sodium hypochlorite solution (a commercial placing in digestor (NOTES 2 and 3). bleach solution containing 5.25-percent NOTE 2. Protective eyeglasses and clothing are available chlorine is satisfactory) to 100 mL mandatory for this procedure because sulfuric with ammonia-free water. acid and high-temperature solutions are very 5.8 Sodium phosphate, dibasic, solution, 71 hazardous. The addition of the above mixture g/L: Dissolve 134 g Na2HPO4-7H2O in approx must be carried out in a hood. 800 mL ammonia-free water. Add 100 mL 5 M NOTE 3. Teflon boiling chips, available from NaOH, dilute to 1 L with ammonia-free water, Cole-Parmer Instrument Co., are preferable. and mix thoroughly. Before use they should be soaked in dilute HC1 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 333 (approx 6M), rinsed several times in ammonia- 6.8 Begin analysis. The cathode-ray tube free water, and dried at 180 °C. In order to avoid (CRT) will acknowledge the parameters and con­ contamination by laboratory fumes, store them centration range, listing each sample-cup in a tightly stoppered container in an ammonia- number and corresponding concentrations free area of the laboratory. calculated from the working curve. During each 6.4 Digest under a hood for 3J/2 h using the run, the CRT display will provide a plot of listed conditions. It is imperative that the standards, samples, and list blank and slope heating block cool to 150°C before subsequent calculations. Retain copy of all information ob­ batches of samples are placed in the digestor or tained from printer. extreme spattering will occur. 6.5 Cautiously, remove tubes from the 7. Calculations digestor and allow to cool for approx 15 min in Determine the concentration in milligrams a hood. Quickly add approx 50 mL ammonia- per liter of dissolved or total ammonia plus free water to each tube with vigorous agitation organic nitrogen in each sample from either the and extreme caution (NOTE 4). Allow to cool CRT display or the printer output. briefly before making the final dilution to the 7.2 To determine concentration of sus­ calibration mark. Stopper the tubes and invert pended total ammonia plus organic nitrogen, several times until well mixed (NOTE 5). If a subtract dissolved-ammonia-plus-organic nitro­ portion of this solution must be diluted to re­ gen concentration from total ammonia-plus- main within the designated concentration organic nitrogen concentration. range, this dilution must be made with 0.20M H2S04. 8. Report NOTE 4. The precipitation of salts is minimized Report nitrogen, ammonia plus organic, by this procedure. A vortex mixer is useful for dissolved (00623), total (00625), and suspended- agitating the water-acid mixture. total (00624), concentrations as follows: 0.2 to NOTE 5. Allow any precipitate that has formed 1.0 mg/L, one decimal; 1.0 mg/L and above, two or any boiling chip flakes to settle before fill­ significant figures. ing the sample cups as described in paragraph 6,8. 9. Precision 6.6 Set up analyzer and computer-card as­ The precision expressed in terms of the stand­ signments according to the manufacturer's in­ ard deviation and percent relative standard structions. deviation for replicate analysis of reference 6.7 Place standards, beginning with the materials by a single operator is as follows: lowest concentration, in ascending order Relative (computer-calibration curve) in the first five standard positions on the sample turntable. These stand­ Mean Number of Standard deviation deviation ards should be 0.2, 0.5, 1.0, 3.0, and 5.0 mg/L (mg/L) replicates (mg/L) (percent) NH3-N. Place samples and quality-control 0.11 10 0.04 36.4 .42 34 .09 21.4 standards in the remainder of the sample 4.2 35 .08 1.9 turntable. 5.0 26 .08 1.6

Nitrogen, ammonia plus organic, colorimetric, digestion-distillation-nesslerization

Parameter and Code: Nitrogen, ammonia plus organic, dissolved, 1-1550-85 (mg/L as N): 00623

1. Application 5. Reagents This method, is recommended for analysis of 5.1 Ammonia standard solution I, 1.00 water containing from 0.01 to 2.0 mg/L of mL = 1.00 mg N: Dissolve 3.819 g NH4C1, dissolved ammonia plus organic nitrogen. dried overnight over sulfuric acid, in ammonia- Samples with greater concentrations need either free water and dilute to 1,000 mL. to be diluted or to be analyzed by a titrunetric 5.2 Ammonia standard solution II, 1.00 procedure. mL = 0.010 mg N: Dilute 10.00 mL ammonia standard solution I to 1,000 mL with ammonia- 2. Summary of method free water. Prepare fresh daily. 2.1 Organic nitrogen-containing compounds 5.3 Borate buffer solution: Dissolve 9.54 g are degraded to ammonium salts by digestion Na2B4O7'10H2O in ammonia-free water. with sulfuric acid in the presence of copper Adjust the pH to 9.5 with 1M NaOH (approx sulfate, which acts as a catalyst. The solution 15 mL), and dilute to 1 L with ammonia-free is then made alkaline with sodium hydroxide, water. and the resulting free ammonia is distilled and 5.4 Boric acid solution, 20 g/L: Dissolve 20 nesslerized. The color developed is proportional g H3BO3 in ammonia-free water and dilute to to the ammonia-plus-organic nitrogen content 1 L. of the sample. 5.5 Copper sulfate solution, 6.5 g/100 mL: 2.2 Additional information on the principle Dissolve 6.5 g CuSO4 (anhydrous) in ammonia- of the determination is given in Kolthoff and free water and dilute to 100 mL. others (1969). 5.6 Methyl red indicator solution, 0.1 g/100 mL: Dissolve 0.1 g methyl red indicator in 100 3. Interferences 3.1 Nitrate and nitrite do not interfere. mL 95-percent ethanol. 3.2 Calcium, magnesium, iron, and sulfide 5.7 Nessler reagent— CAUTION: HgI2 is a interfere with the nesslerization, but the distilla­ deadly poison, and the reagent must be so tion eliminates interference of the metals, and marked: Dissolve 100 g HgI2 and 70 g KI in a sulfides are completely destroyed during the small volume of ammonia-free water. Add this digestion. mixture slowly, with stirring, to a cooled solu­ tion of 160 g NaOH in 500 mL ammonia-free 4. Apparatus water and dilute to 1 L. Allow the reagent to 4.1 Cylinder, graduated, with ground-glass stand at least overnight and filter through a stopper, 50-mL capacity (Corning No. 3002 or fritted-glass crucible. equivalent). 5.8 Sodium hydroxide solution, 10M: 4.2 Kjeldahl distillation apparatus, 800-mL Dissolve 400 g NaOH in ammonia-free water flasks. and dilute to 1 L. 4.3 Spectrometer, for use at 425 nm. 5.9 Sulfuric acid, concentrated (sp gr 1.84). 335 336 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6. Procedure batch of H2SO4 by taking 250 mL ammonia-free 6.1 Rinse all glassware with ammonia-free water through the entire procedure: water before use 6.2 Free the Kjeldahl distillation apparatus mg reagent blank = of ammonia by boiling ammonia-free water until mg ammonia mL aliquot plus organic N the distillate shows no trace using nessler distillate reagent—CAUTION: deadly poison. I per 5.0 mL H2SO4 6.3 Pipet a volume of sample containing less 7.2 Determine the milligrams of ammonia than 1.0 mg ammonia plus organic nitrogen (250 plus organic nitrogen in each sample aliquot from mL max) into a 800-mL Kjeldahl digestion flask. a plot of absorbances of standards. 6.4 Add 5.0 mL concentrated H2SO4 and 0.5 7.3 Determine the ammonia-plus-organic mL CuSO4 solution, and mix. nitrogen concentration in milligrams per liter as 6.5 Digest under a hood until copious fumes are given off. Continue heating until the fumes follows: have subsided and the liquid becomes colorless Ammonia plus organic nitrogen, mg/L = or pale yellow. Continue digestion an additional 30 min. ———1,000-————X————-———X 250 6.6 Cool and dilute to approx 150 mL with mL sample mL aliquot ammonia-free water. 6.7 Add 25 mL 10M NaOH cautiously down [(mg ammonia plus organic N in aliquot)- the side of the flask. (mg reagent blank)]. 6.8 Immediately connect the flask to the distillation apparatus, and cautiously mix the 8. Report contents by gentle swirling. Report nitrogen, ammonia plus organic, 6.9 Distill at a rate of no more than 10 and dissolved (00623), concentrations as follows: less no less than 6 mL/min: collect the distillate in a than 1.0 mg/L, two decimals; 1 mg/L and above, 250-mL volumetric flask containing 25 mL boric two signifcant figures. acid solution. The tip of the delivery tube must be below the surface of the boric acid solution 9. Precision in the receiving flask. 9.1 The standard deviation for dissolved am­ 6.10 Collect approx 150 mL distillate, dilute to monia plus organic nitrogen within the range of the mark with ammonia-free water, and mix. 0.43 to 1.81 mg/L for nine samples was found to 6.11 Pipet an aliquot of distillate containing be independent of concentration. The 95-percent less than 0.1 mg ammonia-nitrogen (50.0 mL confidence interval for the average standard max) into a glass-stoppered, graduated mixing deviation of 0.682 mg/L ranged from 0.603 to cylinder, and adjust the volume to 50.0 mL with 0.786 mg/L. ammonia-free water. 9.2 Precision for dissolved ammonia plus 6.12 Prepare a blank of ammonia-free water and organic nitrogen for four of the nine samples ex­ a series of standards in glass-stoppered, graduated pressed in terms of the percent relative standard mixing cylinders. Add 5 mL boric acid solution deviation is as follows: to each, and adjust the volume of each to 50.0 ™T, 6.13 Add 1.0 mL nessler reagent—CAUTION: Number of Mean Relative standard deviation deadly poison—to each blank, standard, and laboratories (mg/L) _____(percent)_____ sample Stopper and invert several times to mix 11 0.434 58 13 .957 79 thoroughly. 15 1.003 53 6.14 Allow the solutions to stand at least 10 8 1.807 72 min, but not more than 30 min. 6.15 Determine the absorbance of each test sample and standard against that of the blank. Reference Kolthoff, I. M.t Sandeli £. R, Meehen, E. J., and Bracken- 7. Calculations stein, SL, 1969, Quantitative chemical analysis (4th ed): 7.1 Determine a reagent blank for each new New York, Macmillan, 1199 pi Nitrogen, ammonia plus organic, titrimetric, digestion-distillation

Parameter and Code: Nitrogen, ammonia plus organic, total-in-bottom-material, dry wt, 1-5553-85 (mg/kg as N): 00626

1. Application 5.5 Sodium carbonate solution, 0.0357N: This method may be used for analysis of bot­ Dissolve 1.892 g primary standard Na2CO3 in tom material containing at least 10 mg/kg of carbon dioxide-free water and dilute to 1,000 total ammonia plus organic nitrogen. Only that mL. portion of bottom material that passes a 2-mm 5.6 Sodium hydroxide-thiosulfate solution: sieve is taken for analysis (method P-0810, sub- Cautiously, dissolve 500 g NaOH in 600 mL sampling, bottom material, coring). ammonia-free water. Add 80 g Na2S2O3-5H2O and dilute to 1 L. 2. Summary of method 5.7 Sodium thiosulfate, crystals, Na2S2O3- The sample is subjected to a digestion where­ 5H20. by all organic nitrogen-containing compounds 5.8 Sucrose. are converted to ammonium salts. The resulting 5.9 Sulfuric acid, concentrated, sp gr 1.84. mixture is then made strongly alkaline, and the 5.10 Sulfuric acid standard solution, approx ammonia so formed is distilled from the mixture 0.0367V; Cautiously, add 1.0 mL concentrated into a solution of boric acid and subsequently H2SO4 (sp gr 1.84) to 800 mL ammonia-free determined by titration with standard sulfuric water and dilute to 1 L. Standardize by titrating acid solution. 25.0 mL 0.0357AT Na2CO3 to pH 4.5. Compute normality of sulfuric acid standard solution to 3. Interferences four decimal places. There are no known interferences with this method. 6. Procedure 6.1 Free the distillation apparatus of am­ 4. Apparatus monia by boiling ammonia-free water until the Kjeldahl distillation apparatus, 500-mL distillate shows no trace using nessler reagent— flasks. CAUTION: deadly poison. 6.2 Weigh to the nearest milligram, 3 g of 5. Reagents bottom-material sample, prepared as directed in 5.1 Ammonium chloride, crystals. method P-0810, and transfer to the digestion 5.2 Boric acid solution, 20 g/L: Dissolve 20 flask. g H3BO3 crystals in 800 mL ammonia-free 6.3 In the same manner prepare a blank, us­ water and dilute to 1 L. ing 2.0 g sucrose. Analyze the blank and each 5.3 Digestion catalyst: Tablets containing sample as directed in paragraphs 6.4 to 6.10. 3.5 g K2SO4 and 0.175 g HgO (Scientific Chem­ 6.4 Cautiously, add 25 mL concentrated ical Technical Sales Inc., SCT Kel-catalyst No. H2SO4 (sp gr 1.84), and under a hood, swirl the KC-M3, or equivalent). contents of the flask until thoroughly mixed. 5.4 Mixed indicator solution: Dissolve 20 mg 6.5 Add three digestion-catalyst tablets and methyl red and 100 mg bromocresol green in mix well. Add a few glass beads and begin the 100 mL 95-percent ethanol. Store in a well- digestion. Continue the digestion until a dear so­ sealed bottle. lution is obtained, and then continue fuming 1 h.

337 338 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6.6 Cool the flask until crystals appear (do X Na X 14,000 not cool completely). Add 150 mL ammonia-free water; mix and allow to cool. Wt0 6.7 Add 100 mL NaOH-Na2S2O3 solution. Immediately connect the flask to the distillation where apparatus and cautiously mix the contents by swirling. Va = volume of standard H2SO4 used to 6.8 Distill at a rate of not more than 10 titrate sample, milliliters, minus mL/min and no less than 6 mL/min; collect the volume used to titrate blank, distillate in a 250-mL volumetric flask contain­ milliliters, ing 25 mL boric acid solution. The tip of the Na — normality of standard H2SO4 solution, delivery tube must be below the surface of the and boric acid solution in the receiving flask. 6.9 Collect approx 200 mL of distillate, WtQ = weight of sample, grams. dilute to 250 mL with ammonia-free water, and mix. 8. Report 6.10 To the distillate, add 3 drops mixed in­ Report nitrogen, ammonia plus organic, total- dicator solution, and titrate with sulfuric acid in-bottom-material (00626), concentrations as standard solution until the color of the solution follows: 10 to 100 mg/kg, nearest 1 mg/kg; 100 changes from yellow to red. mg/kg and above, two significant figures.

7. Calculations 9. Precision Precision data are not available for this Nitrogen, ammonia plus organic (mg/kg) = method. Nitrogen, nitrate, ion-exchange chromatographic, automated

Parameters and Codes: Nitrogen, nitrate, dissolved, 1-2057-85 (mg/L as N): 00618 Nitrogen, nitrate, dissolved, I-2058-85 (mg/L as N): 00618

2. Summary of method anions in their acid form are measured using an Nitrate is determined sequentially with six electrical-conductivity cell. See method 1-2057, other anions by ion-exchange chromatography. anions, ion-exchange chromatographic, auto­ Ions are separated based on their affinity for mated, and method 1-2058, anions, ion-exchange the exchange sites of the resin. The separated chromatographic, precipitation, automated.

339

Nitrogen, nitrite, colorimetric, diazotization

Parameter and Code: Nitrogen, nitrite, dissolved, 1-1540-85 (mg/L as N): 00613

1. Application solution in the dark and protect from nitrogen This method may be used to analyze water oxides that may be in the atmosphere. The solu­ containing between 0.01 and 0.6 mg/L of nitrite- tion is stable for several months. nitrogen; samples containing greater concentra­ 5.2 Nitrite-nitrogen standard solution /, 1.00 tions need to be diluted. mL = 0.50 mg NO2-N: Dissolve 3.038 g KNO2 in demineralized water and dilute to 1,000 mL. 2. Summary of method This and the following nitrite standard solution Nitrite is diazotized with sulfanilamide, and are not stable indefinitely; their concentrations the resulting diazo compound is coupled with must be checked frequently. N-1-naphthylethylenediamine dihydrochloride 5.3 Nitrite-nitrogen standard solution II, to form an intensely colored red compound, 1.00 mL = 0.05 mg NO2-N: Dilute 100.0 mL which is determined spectrometrically at 540 nitrite-nitrogen standard solution I to 1,000 mL nm. Sulfanilamide and N-1-naphthylethylene- with demineralized water. diamine dihydrochloride are combined with a sodium acetate buffer to form a single reagent 6. Procedure solution. 6.1 Pipet a volume of sample containing less than 0.03 mg NO2-N (50.0 mL max) into a 3. Interferences 100-mL beaker and adjust the volume to 50.0 Oxidizing agents interfere by oxidizing nitrite mL with demineralized water (NOTE 1). to nitrate. Sulfide also interferes. No other sub­ NOTE 1. If the sample has a pH greater than stance commonly occurring in natural water in­ 10 or less than 4 (or greater than 600 mg/L terferes with this method. alkalinity or acidity), adjust to approx pH 6 with 3M HC1 or 2.5M NaOH. 4. Apparatus 6.2 Prepare a blank and sufficient stand­ 4.1 Spectrometer for use at 540 nm. ards, and adjust the volume of each to 50.0 mL 4.2 Refer to manufacturer's manual to op­ (NOTE 2). timize instrument. NOTE 2. If the samples were preserved with mercuric chloride fortified with sodium chloride, 5. Reagents add an equivalent amount to the blank and 5.1 Color-buffer solution: Add 105 mL con­ standards. centrated HC1 (sp gr 1.19), 5.0 g sulfanilamide, 6.3 Add 2.0 mL color-buffer solution and mix. and 0.5 g N-1-naphthylethylenediamine dihy­ 6.4 Allow the color to develop for at least 15 drochloride to 250 mL demineralized water. Stir min and measure the absorbances of the sample until dissolved. Add 136 g CH3COONa-3H2O and standards against that of the blank. or 82 g CH3COONa and stir until dissolved. Dilute to 500 mL with demineralized water. 7. Calculations When 2 mL of this solution is added to 50 mL 7.1 Determine milligrams of nitrite-nitrogen demineralized water, the resultant solution in each test sample from a plot of absorbances should have a pH of 1.8. Store the color-buffer of standards. 341 342 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 7.2 Determine the nitrite-nitrogen concen­ ST = 0.096X + 0.006 tration in milligrams per liter as follows: where NO2-N

Parameters and Codes: Nitrogen, nitrite, dissolved, 1-2540-85 (mg/L as N): 00613 Nitrogen, nitrite, total, I-4540-85 (mg/L as N): 00615

1. Application 5. Reagents 1.1 This method may be used to analyze sur­ 5.1 Color reagent: Add 200 mL concentrated face, domestic and industrial water, and brines phosphoric acid (sp gr 1.69) and 20 g sulfanila­ and water-suspended sediment containing from mide to approx 1,500 mL demineralized water. 0.01 to 1.0 mg/L of nitrite-nitrogen. Samples Dissolve completely (warm if necessary). Add containing greater concentrations need to be 1.0 g N-1-naphthylethylenediamine dihydro­ diluted. chloride and dissolve completely. Dilute to 2 L 1.2 Water-suspended sediment may be ana­ with demineralized water. Store in an amber lyzed by this procedure by decanting a suitable bottle and refrigerate; however, the reagent portion from a well-settled sample. must be at room temperature when it is used. The reagent is stable for approx 1 month. 2. Summary of method 5.2 Nitrite-nitrogen standard solution /, 1.00 Nitrite ion reacts with sulfanilamide under mL = 0.100 mg NO2-N: Dissolve 0.6076 g acidic conditions to form a diazo compound, KNO2 in demineralized water and dilute to which then couples with N-1-naphthylethylene- 1,000 mL. This and the following nitrite stand­ diamine dihydrochloride to form a red com­ ard solutions are not stable indefinitely; their pound, the absorbance of which is measured concentrations must be checked frequently. colorimetrically (Kamphake and others, 5.3 Nitrite-nitrogen standard solution II, 1967). 1.00 mL = 6.010 mg NO2-N: Quantitatively dilute 100.0 mL nitrite-nitrogen standard 3. Interferences solution I to 1,000 mL with demineralized Oxidizing agents interfere by oxidizing nitrite water. to nitrate. Sulfide also interferes. No other 5.4 Nitrite-nitrogen working standards: substance commonly occurring in natural water Prepare a blank and 100 mL each of a series of interferes with this method. nitrite-nitrogen working standards by appro­ priate quantitative dilution of nitrite-nitrogen 4. Apparatus standard solution II. Dissolve 5.2 mg mercuric 4.1 Technicon AutoAnalyzer II, consisting chloride and 60 mg sodium chloride in each of sampler, cartridge manifold, proportioning working standard. For example: pump, colorimeter, voltage stabilizer, recorder, and printer. Nitrite-nitrogen standard solution tl Nitrite-nitrogen concentration 4.2 With this equipment the following oper­ (mL) (mg/L) ating conditions have been found satisfactory: 0.0 0.00 Absorption cell ——— 15 mm .5 .05 2.0 .2 Wavelength ————— 520 nm 5.0 .5 Cam —————————— 40/h (4/1) 10.0 1.0

343 344 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6. Procedure 7.2 Compute the concentration of dissolved 6.1 Set up manifold (fig. 35). or total nitrite-nitrogen in each sample by com­ 6.2 Allow colorimeter and recorder to warm paring its height to the analytical curve* Any for at least 30 min. baseline drift that may occur must be taken into 6.3 Adjust the baseline to read zero scale account when computing the height of a sam­ divisions on the recorder with all reagents, but ple or standard peak. with demineralized water in the sample tube. 6.4 Place a complete set of standards and a 8. Report blank in the first positions of the first sample Report nitrogen, nitrite, dissolved (00613), tray, beginning with the most concentrated and total (00615), concentrations as follows: less standard. Place individual standards of differ­ than 1 mg/L, two decimals; 1 mg/L and above, ing concentrations in approximately every two significant figures. eighth position of the remainder of this and subsequent sample trays. Fill remainder of each 9. Precision tray with unknown samples. 9.1 Precision for dissolved nitrite-nitrogen 6.5 Begin analysis. When the peak from the for 19 samples within the range of 0.006 to 2.22 most concentrated working standard appears mg/L may be expressed as follows: on the recorder, adjust the STD CAL control until the flat portion of the peak reads full scale. 0.004 7. Calculations 7.1 Prepare an analytical curve by plotting where the height of each standard peak versus its ST SB overall precision, milligrams per liter, respective nitrite-nitrogen concentration. and

0.030 in Air 0.32 mL/min 10- turn coil nmn ' 0.056 in Water* j i j 1.20 mL/min 0.025 in Sample -0 2(Hum coils 0.23 mL/min 0.030 in Color reagent 0.32 mL/min Sampler 4 C iolorimeter T 40/h ?0 nm .Waste To sampl er 4 5; h + 0.073in Water 4/1 cam 1!i- mm cell/ was i ecepl acle 2.00 mL/min T -s:pi 0.045in Waste 0.80 mL/min Recorder Proportioning pump

Contains 0.5-mL Brij solution per liter Figure 35.—Nitrogen, nitrite, diazotization manifold METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 345 X = concentration of nitrite-nitrogen, milli­ 9.3 It is estimated that the percent relative grams per liter. standard deviation for total nitrite-nitrogen will The correlation coefficient is 0.9445. be greater than that reported for dissolved 9.2 Precision for dissolved nitrite-nitrogen for nitrite-nitrogen. six of the 19 samples expressed in terms of the percent relative standard deviation is as follows:

Number of Mean Relative standard deviation laboratories (mg/L) _____(percent)_____ Reference 13 0.006 133 14 .010 60 20 .050 16 20 .540 6 Kamphake, L.t Hannah, S., and Cohen, J., 1967, Automated 21 1.40 13 analysis for nitrite by hydrazine reduction: Water 19 2.22 9 Research, v. 1, p. 205-16.

Nitrogen, nitrite, colorimetric, diazotization, automated-discrete

Parameters and Codes: Nitrogen, nitrite, dissolved, 1-2539-85 (mg/L as N): 00613 Nitrogen, nitrite, total, I-4539-85 (mg/L as N): 00615

1. Application Sample volume 0.125 mL with 0.100 mL 1.1 This method may be used to analyze sur­ diluent (NOTE 1) face, domestic, and industrial water, and water- Reagent volume 1.0 mL color reagent suspended sediment containing from 0.01 to (NOTE 1) 1.00 mg/L of nitrite-nitrogen. Samples contain­ ing concentrations greater than 1.0 mg/L need NOTE 1. Sample-to-diluent ratio and reagent to be diluted. volume must be optimized for each instrument 1.2 Water-suspended sediment may be according to manufacturer's specifications. analyzed by this procedure by decanting a suitable portion from a well-settled sample. 5. Reagents 5.1 Color reagent: Add 100 mL concentrated 2. Summary of method phosphoric acid (sp gr 1.69) and 10 g sulfanila­ Nitrite ion reacts with sulfanilamide under mide to approx 750 mL demineralized water. acidic conditions to form a diazo compound, Dissolve completely (warm if necessary). Add which then couples with N-1-naphthylethylene- 0.5 g N-1-naphthylethylenediamine dihydro­ diamine dihydrochloride to form a red-colored chloride and dissolve completely. Dilute to 1000 compound, the absorbance of which is measured mL with demineralized water. Store in an amber colorimetrically (Kamphake and others, 1967). bottle and refrigerate. Solution is stable for ap­ prox 1 month. 3. Interferences 5.2 Nitrite-nitrogen standard solution /, 3.1 Oxidizing agents interfere by oxidizing 1.00 mL = 1.00 mg NO2-N: Dissolve 6.076 g nitrite to nitrate. Sulfide also interferes. No KNO2 in demineralized water and dilute to other substance commonly occurring in natural 1000 mL. This and the following nitrite water interferes. standard solutions are not stable indefi­ nitely; their concentrations must be checked 4. Apparatus frequently. 4.1 Discrete chemical analyzer system, 5.3 Nitrite-nitrogen standard solution II, American Monitor IQAS or equivalent. 1.00 mL = 0.01 mg NO2-N: Quantitatively 4.2 With this equipment, the following dilute 10.0 mL nitrite-nitrogen standard so­ operating conditions have been found satisfac­ lution I to 1000 mL with demineralized tory for the range 0.01 to 1.00 mg/L: water. Wavelength — 547 nm 5.4 Nitrite-nitrogen working standards: Absorption cell 1 cm square, Prepare a blank and 1000 mL each of a series temperature-controlled, of nitrite-nitrogen working standards by dilu­ flow-through quartz tion of nitrite-nitrogen standard solution II. cuvette Dissolve 52 mg mercuric chloride and 600 mg Reaction tem­ sodium chloride in each working standard. For perature —— 37 °C example:

347 348 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Nitrite-nitrogen standard solution II Nitrite-nitrogen concentration 7. Calculations (ml) (mg/L) Determine the concentration in milligrams 0.0 0.00 per liter of dissolved or total nitrite-nitrogen in 2.0 .02 each sample from either the CRT display or the 5.0 .05 30.0 .30 printer output. 100.0 1.00 8. Report 6. Procedure Report nitrogen, nitrite, dissolved (00613), 6.1 Set up the analyzer and computer-card and total (00615), concentrations as follows: less assignments according to manufacturer's in­ than 1.0 mg/L, two decimals; 1.0 mg/L and structions. above, two significant figures. 6.2 Place standards, beginning with the lowest concentrations, in ascending order (com­ 9. Precision puter-calibration curve) in the first five posi­ The precision expressed in terms of the stand­ tions on the sample turntable. Place samples ard deviation and percent relative standard and quality-control standards in the remainder deviation for replicate analysis of reference of the sample turntable. materials by a single operator is as follows: 6.3 Begin analysis. The cathode-ray tube (CRT) will acknowledge the parameter and con­ Relative centration range, listing each sample-cup num­ standard Mean Number of Standard deviation deviation ber and corresponding concentrations calcu­

Parameter and Code: Nitrogen, nitrite, dissolved, 1-2057-85 (mg/L as N): 00613

2. Summary of method exchange sites of the resin. The separated anions Nitrite is determined sequentially with six in their acid form are measured using an electri­ other anions by ion-exchange chromatography. cal-conductivity cell See method 1-2057, anions, Ions are separated based on their affinity for the ion-exchange chromatographic (1C), automated 349

Nitrogen, nitrite plus nitrate, colorimetric, cadmium reduction-diazotization, automated-segmented flow

Parameters and Codes: Nitrogen, nitrite plus nitrate, dissolved, 1-2545-85 (mg/L as N): 00631 Nitrogen, nitrite plus nitrate, total, I-4545-85 (mg/L as N): 00630 Nitrogen, nitrite plus nitrate, total-in-bottom-material, dry wt, I-6545-85 (mg/kg as N): 00633

1. Application adjusting the pH of the ammonium chloride buf­ 1.1 This method may be used to analyze sur­ fer to 6.3. face, domestic, and industrial water, and brines and water-suspended sediment containing from 3. Interferences 0.1 to 5.0 mg/L of nitrite- plus nitrate-nitrogen. 3.1 The concentrations of potentially in­ Samples containing greater concentrations need terfering substances are seldom high enough to to be diluted. introduce error. High concentrations of oxidiz­ 1.2 Water-suspended sediment may be ana­ ing agents, reducing agents, and some metals, lyzed by this procedure by decanting a suitable such as Cu+2, interfere. See American Society portion from a well-settled sample. for Testing and Materials (1984) for details on 1.3 This method may be used to determine potential interferences. the sum of nitrite- plus nitrate-nitrogen concen­ 3.2 Acids destroy the cadmium column; trations in bottom material containing at least therefore, acid-treated samples cannot be ana­ 2 mg/kg. lyzed by this method. 3.3 Repeated analysis of waters containing 2. Summary of method concentrations of sulfide more than 2 mg/L will 2.1 An acidified sodium chloride extraction rapidly deactivate the cadmium column by for­ procedure is used to extract nitrate and nitrite mation of cadmium sulfide (Strickland and Par­ from bottom material for this determination sons, 1972). (Jackson, 1958). 2.2 Nitrate is reduced to nitrite by a copper- 4. Apparatus cadmium column. The sample stream is then 4.1 Centrifuge. treated with sulf anilamide under acidic condi­ 4.2 Shaker, wrist-action. tions to yield a diazo compound, which couples 4.3 Technicon AutoAnalyzer II, consisting with N-1-naphthylethylenediamine dihydro- of sampler, cartridge manifold (including chloride to form a red compound, the absorb- copper-cadmium reduction column), proportion­ ance of which is measured colorimetrically. The ing pump, colorimeter, voltage stabilizer, re­ final result is the sum of the nitrite originally corder, and printer. present plus that formed by the reduction of the 4.4 With this equipment the following nitrate (Brewer and Riley, 1965; Kamphake and operating conditions have been found satisfac­ others, 1967; Morris and Riley, 1963; Strickland tory for the range from 0.1 to 5.0 mg/L and Parsons, 1972; U.S. Environmental Protec­ (NO2 + NO3) as N: tion Agency, 1979, p. 207-214; and Ehrlich and MacDonald, written commun., 1969). Absorption cell ——— 15 mm 2.3 Interferences from Hg+2 added to the Wavelength ————— 520 nm samples as a preservative are overcome by Cam ————————— 40/h (4/1) 351 352 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

5. Reagents Nitrite-nitrogen standard solution II Nitrite-nitrogen concentration 5.1 Ammonium chloride solution, 10 g/L: (ml) (mg/L) Dissolve 10 g NH4C1 in demineralized water 0.0 0.00 2.0 .10 and dilute to approx 950 mL. Adjust pH to 5.0 .25 6.3 ± 0.2 with dilute NH4OH solution and 10.0 .5 dilute to 1 L. Add 0.5 mL Brij-35 solution. 20.0 1.0 30.0 1.5 5.2 Brij-35 solution, 30-percent aqueous solu­ 40.0 2.0 tion (Baker No. C706 or equivalent). 60.0 3.0 5.3 Cadmium powder, coarse, 99 percent 80.0 4.0 pure (Technicon No. Til-5063, or equivalent): 100.0 5.0 Wash cadmium powder with diethyl ether or 1M HC1 followed by demineralized water. Allow NOTE 1. If nitrate-nitrogen in bottom material to air-dry. Shake the dry powder with copper is being determined, the working standards are sulfate solution (20 g/L). The weight of the solu­ diluted with sodium chloride solution (5.10). tion should be approx 10 times that of the cad­ Mercuric chloride is not added. mium. Wash thoroughly with demineralized 5.10 Sodium chloride solution, 100 g/L, water to remove colloidal copper, which is visi­ acidified: Dissolve 100 g NaCl in 950 mL ble as a blue color in the wash solution. A ammonia-free water. Acidify with concentrated minimum of 10 washings is usually required to HC1 (sp gr 1.19) to a pH of 2.5. Dilute to 1 L. eliminate perceptible blue color. 5.4 Color reagent: Add 200 mL concentrated 6. Procedure phosphoric acid (sp gr 1.69) and 20 g 6.1 Proceed to paragraph 6.2 for waters or sulfanilamide to approx 1,500 mL demineralized water-suspended sediment mixtures. For bot­ water. Dissolve completely (warm if necessary). tom materials begin with paragraph 6.1.1. Add 1.0 g N-1 -naphthylethylenediamine 6.1.1 Weigh approx 5 g of sample, prepared dihydrochloride and dissolve completely. Dilute as directed in either method P-0520 or P-0810, to 2 L with demineralized water. Add 1.0 mL and transfer to a 250-mL Erlenmeyer flask. Brij-35 solution. Store in a refrigerator. This 6.1.2 Add 50 mL NaCl solution (5.10) and reagent is stable for approx 1 month. shake on the wrist-action shaker for 30 min. 5.5 Copper sulfate solution, 20 g/L: Dissolve 6.1.3 Carefully transfer the entire sample, in­ 20 g CuSO4 (anhydrous) in demineralized water cluding all sediment particles, to a centrifuge and dilute to 1 L. tube. Centrifuge for 5 min; if the sample does 5.6 Hydrochloric acid, l.OM: Add 83.3 mL not flocculate, add a drop of concentrated HC1 concentrated HC1 (sp gr 1.19) to demineralized (sp gr 1.19) and recentrifuge. water and dilute to 1 L. 6.1.4 Transfer the supernatant solution to a 5.7 Nitrate-nitrogen standard solution I, 100-mL volumetric flask, taking care not to 1.00 mL = 0.50 mg NO3-N: Dissolve 3.609 g disturb the residue in the bottom of the cen­ KN03, dried overnight over concentrated trifuge tube. H2SO4, in demineralized water and dilute to 6.1.5 Wash the sediment in the centrifuge 1,000 mL. tube with 20 mL sodium chloride solution, 5.8 Nitrate-nitrogen standard solution II, recentrifuge, and transfer the clear wash solu­ 1.00 mL = 0.025 mg NO3-N: Dilute 50.0 mL tion to the volumetric flask. Adjust to volume nitrate-nitrogen standard solution I to 1,000 mL with sodium chloride solution (5.10). Proceed to with demineralized water. paragraph 6.2. 5.9 Nitrate-nitrogen working standards*. 6.2 Set up manifold (fig. 36). Prepare a blank and 500 mL each of a series of 6.3 Allow the color reagent to come to room nitrate-nitrogen working standards by ap­ temperature. propriate quantitative dilution of nitrate stand­ 6.4 Allow colorimeter and recorder to warm ard solution II (NOTE 1). Dissolve 26 mg for at least 30 min. mercuric chloride and 300 mg sodium chloride 6.5 Fill the reduction column, which is a U- in each working standard. For example: shaped, 36-cm length of 2.0-mm ID glass tubing METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 353

To waste (!)-«— Cadmium-reduction * 5-turn O.OSOin Air column coil 0.32 mL/min (mm) O.OSGin Ammonium chloride 1.20 mL/min 0.020in Sample 0.16 mL/min 0.045 in Waste(l) 0.80 mL/min Sampler 4 O.OSOin Air 407 h 0.32 mL/min 4/1 cam Colorimeter 0.030in Color reagent 520 nm -rWaste 0.32 mL/min 15- mm eel To sampler 4 Water wash 0.073in 2.00 mL/min receptacle 0.045 in Waste (2) 0.80 mL/min Recorder Proportioning pump

*0.034in polyethylene Figure 36.—Nitrogen, nitrite plus nitrate, cadmium reduction-diazotization, manifold

(Tfechnicon Na 189-0000 or equivalent), with 6.7 Activate and stabilize the reduction col­ water. This prevents entrapment of air bubbles umn by pumping a 3.0 mg/L NO3-N standard when filling the tube with cadmium. Transfer the through the sample line until a steady state is prepared cadmium granules to the reduction col­ attained. umn. After filling is completed, insert borosilicate 6.8 Switch to demineralized water in the sam­ glass wool in the exit end of the tuba This col­ ple line and adjust the baseline to read zero scale umn should function for several hundred samples divisions on the recorder. before it needs to be refilled (NOTE 2). 6.9 Place a complete set of standards and two NOTE 2. The reduction efficiency of the column blanks in the first positions of the first sample should be checked regularly by comparing the tray, beginning with the most concentrated stand­ peak heights of nitrite and nitrate standards. ard Place individual standards of differing concen­ Equal concentration standards should give equal trations in every eighth position of the remainder heights. Replace the column if the efficiency falls of this and subsequent sample trays. Fill remain­ below 90 percent. der of each sample tray with unknown samples. 6.6 Begin pumping reagents, but do not con­ 6.10 Begin analysis. When the peak from the nect the reduction column to the manifold most concentrated working standard appears on system until air has been pumped from the the recorder, adjust the STD CAL control until reagent and sample tubes (NOTE 3). the flat portion of the peak reads full scale. NOTE 3. It is important to avoid introduction of air bubbles into the reduction column, because 7. Calculations they adversely affect sample contact with the 7.1 Prepare an analytical curve by plotting cadmium powder and decrease the reduction ef­ the height of each standard peak versus its ficiency. Column must be replaced if air bubbles respective nitrite- plus nitrate-nitrogen concen­ are introduced. tration. 354 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 7.2 Compute the concentration of dissolved where or total nitrite- plus nitrate-nitrogen in = overall precision, milligrams per liter, milligrams per liter in each sample by compar­ and ing its peak height to the analytical curve. Any X concentration of nitrogen, milligrams per baseline drift that may occur must be taken in­ liter. to account when computing the height of a sam­ The correlation coefficient is 0.6826. ple or standard peak. 9.2 Precision for dissolved nitrite- plus 7.3 Compute the concentration of nitrite- nitrate-nitrogen for five of the 18 samples ex­ plus nitrate-nitrogen in bottom material pressed in terms of the percent relative stand­ samples in milligrams per liter in each sample ard deviation is as follows: by comparing its peak height to the analytical curve. Any baseline drift that may occur must Number of Mean Relative standard deviation be taken into account when computing the laboratories (mg/L) _____(percent)_____ height of a sample or standard peak. 24 0.62 8 4 1.05 4 9 1.27 16 16 2.38 16 X 100 24 5.05 8 NO3-N + NO2-N (mg/kg) = wt of sample (g) 9.3 It is estimated that the percent relative standard deviation for total nitrite- plus nitrate- where nitrogen and for total nitrite- plus nitrate- nitrogen in bottom material will be greater than -AT NO3-N + NO2-N concentration in sam­ that reported for dissolved nitrite- plus nitrate- ple, milligrams per liter. nitrogen.

8. Report References 8.1 Report nitrogen, nitrite plus nitrate, dis­ solved (00631), and total (00630), concentrations American Society for Testing and Materials, 1984, Annual as follows: 0.1 to 1.0 mg/L, two decimals; 1.0 book of ASTM standards, section 11, water: Phila­ delphia, v. 11.01, p. 559-71. mg/L and above, two significant figures. Brewer, P. G., and Riley, J. P., 1965, The automatic deter* 8.2 Report nitrogen, nitrite plus nitrate, mination of nitrate in sea water: Deep Sea Research, total-in-bottom-material (00633), concentrations v. 12, p. 765-72. as follows: less than 10 mg/kg, one decimal; 10 Kamphake, LM Hannah, S., and Cohen, J., 1967, Automated mg/kg and above, two significant figures. analysis for nitrate by hydrazine reduction: Water Research, v. 1, p. 205-16. Morris, A. W., and Riley, J. P., 1963, The determination of 9. Precision nitrate in sea water: Analytica Chimica Acta, v. 29, 9.1 Precision for dissolved nitrite- plus p. 272-9. nitrate-nitrogen for 18 samples within the range Strickland, J. D. H., and Parsons, T. R., 1972, A manual of 0.62 to 5.0 mg/L may be expressed as follows: of sea water analysis: Canada Fisheries Research Board Bull. 167, 310 p. U.S. Environmental Protection Agency, 1979, Methods for the chemical analysis of water and wastes: Washington, ST = 0.120X -I- 0.009 U.S. Government Printing Office, p. 353.2-1. Nitrogen, nitrite plus nitrate, colorimetric, hydrazine reduction-diazotization, automated-discrete

Parameters and Codes: Nitrogen, nitrite plus nitrate, dissolved, 1-2543-85 (mg/L as N): 00631 Nitrogen, nitrite plus nitrate, total, I-4543-85 (mg/L as N): 00630

1. Application 4.2 With this equipment, the following oper­ 1.1 This method may be used to determine the ating conditions have been found satisfactory for concentration of the sum of nitrite- plus nitrate- the range 0.01 to 3.0 mg/L: nitrogen in surface, ground, domestic, and Wavelength — 520 nm industrial water, and water-suspended sediment Absorption cell 1 cm square, in the range from 0.01 to 3.0 mg/L. Samples temperature- containing greater concentrations need to be controlled, flow- diluted. through quartz 1.2 Water-suspended sediment may be cuvette analyzed by this procedure by decanting a Reaction temper­ suitable portion from a well-settled sample. ature ———— 37 °C Sample volume 0.13 mL with 2. Summary of method 0.27 mL of Nitrate is reduced to nitrite with hydrazine diluent (NOTE 1) sulfate in alkaline solution. The nitrite (that Reagent volumes 0.25 mL NaOH, 0.25 originally present plus reduced nitrate) is then mL working reduc- treated with sulfanilamide under acidic condi­ tant solution, and tions to yield a diazo compound, which is 0.80 mL color coupled with N-1-napthylethylenediamine reagent (NOTE 1) dihydrochloride to form a red azo dye. The ab- NOTE 1. Sample-to-diluent ratio and reagent sorbance of this dye is measured colorimetrical- volumes must be optimized for each instrument ly at 520 nm (Kamphake and others, 1967; U.S. according to manufacturer's specifications. Environmental Protection Agency, 1979). 5. Reagents 3. Interferences 5.1 Color reagent: Add 100 mL concentrated 3.1 Sample color that absorbs at the spec- H3PO4 (sp gr 1.69) and 10 g sulfanilamide to 750 trophotometric wavelength used for analysis mL demineralized water and warm if necessary will interfere and must be corrected if the color for complete dissolution. Add 0.5 g exceeds 50 platinum cobalt units. N-1-napthylethylenediamine dihydrochloride and 3.2 Samples containing concentrations greater dissolve completely. Dilute to 1000 mL with than 5000 mg/L sulfate, 1000 mg/L calcium, sodi­ demineralized water. Store in a dark bottle in a um, potassium, or chloride, 150 mg/L magnesium, refrigerator. Solution must be at room 30 mg/L phosphate, and 2 mg/L sulfide interfere. temperature before use. Solution is stable for ap­ proximately one month. 4. Apparatus 5.2 Copper sulfate solution, 4 g/L: Dissolve 4 4.1 Discrete analyzer system, American g CuSO4 (anhydrous) in 500 mL demineralized Monitor IQAS or equivalent. water and dilute to 1000 mL.

355 356 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Hydrazine sulfate solution, 27.5 g/L: 6.2 Place four standards (0.1, 0.5, 1.0, and Dissolve 13.75 g N2H4-H2SO4 in 400 mL 3.0 mg/L NO3-N, respectively) and blank, begin­ demineralized water and dilute to 500 mL— ning with the lowest concentration in the first CAUTION: Poisonous. positions, on the sample turntable. Fill re­ 5.4 Nitrate-nitrogen standard solution /, mainder of turntable with samples. 1.00 mL = 0.50 mg NO3-N: Dissolve 3.609 g 6.3 Begin analysis. The cathode-ray tube KNO3> dried overnight over concentrated (CRT) will acknowledge the parameter and con­ H2SO4, in demineralized water and dilute to centration range, listing each sample-cup 1,000 mL. number and corresponding concentrations 5.5 Nitrate-nitrogen standard solution II, calculated from the working curve. During each 1.00 mL = 0.025 mg NO3-N: Dilute 50.0 mL run the CRT display will provide a plot of stand­ nitrate-nitrogen standard solution I to 1000 mL ards, samples, and list blank and slope calcula­ with demineralized water. tions. Retain copy of all information obtained 5.6 Nitrate-nitrogen working standards: from printer. Prepare a blank and 500 mL each of a series of nitrate-nitrogen working standards by ap­ 7. Calculations propriate dilution of the nitrate standard solu­ Determine the concentration in milligrams tion II. Dissolve 26 mg mercuric chloride and per liter of dissolved or total nitrite plus nitrate- 300 mg sodium chloride in each working stand­ nitrogen in each sample from either the printer ard. For example: output or the CRT display.

Nit rite-nitrogen standard solution II Nitrite-nitrogen concentration (mL) (mg/L) 8. Report Report nitrogen, nitrite plus nitrate, dissolved 0.0 0.00 1.0 .05 (00631) and total (00630), concentrations as 2.0 .10 follows: less than 1.0 mg/L, nearest 0.01 mg/L; 10.0 .50 1.0 mg/L and above, two significant figures. 20.0 1.0 60.0 3.0 9. Precision 5.7 Sodium hydroxide solution, 0.3M: Precision expressed in terms of the standard Dissolve 12 g NaOH in 500 mL demineralized deviation and percent relative standard devia­ water and dilute to 1000 mL. tion for replicate analyses of reference materials 5.8 Working reductant solution: Add 13.5 by a single operator are as follows: mL hydrazine sulfate solution plus 8 mL cop­ Relative per sulfate solution to 500 mL demineralized standard Number of Mean Standard deviation deviation water and dilute to 1000 mL. Prepare fresh replicates (mg/L) (mg/L) (percent) daily. 40 0.10 0.01 10 40 .24 .02 8 6. Procedure 17 .31 .03 10 6.1 Set up the analyzer and computer-card 40 .50 .02 4 40 1.01 .02 2 assignments according to the manufacturer's 16 1.63 .08 5 instructions. Add the 0.3M NaOH solution from 57 3.05 .09 3 the first available dispensing station and the working reductant solution from the last available dispensing station. The color reagent References is added from a dispensing station during a sec­ ond cycle of the turntable (NOTE 2). Kamphake, L., Hannah, S., and Cohen, J.t 1967, Automated NOTE 2. This second cycle of the turntable is analysis for nitrate by hydrazine reduction: Water Research, V. 1, p. 205. necessary to ensure complete reduction of U.S. Environmental Protection Agency, 1979, Methods for nitrate to nitrite prior to the formation of the chemical analyses of water and wastes: Cincinnati, red-colored azo dye. p. 353.1-1. Oxygen demand, chemical (COD), colorimetric, dichromate oxidation

Parameter and Code: Oxygen demand, chemical, total, 1-3561-85 (COD in mg/L): 00340

1. Application 5. Reagents This method may be used to analyze water- 5.1 Potassium acid phthalate standard solu­ suspended sediment containing between 10 and tion 7,1.0 mL = 10.0 mg COD: Dissolve 8.500 500 mg/L chemical oxygen demand (COD). g potassium acid phthalate, which has been dried for 2 h at 110°C, in demineralized water 2. Summary of method and dilute to 1,000 mL. 2.1 Organic and other oxidizable materials 5.2 Potassium acid phthalate standard solu­ are oxidized by digestion with an acid-dichro tion II, 1.0 mL = 1.0 mg COD: Dilute 100 mL mate solution in the presence of silver sulfate potassium acid phthalate standard solution I to catalyst. The COD concentration is determined 1,000 mL with demineralized water. This solu­ spectrometrically by measuring the absorbance tion is used to prepare working standards at of the Cr+3 that is formed. time of analysis. 2.2 Additional information about the prin­ 5.3 Potassium dichromate-mercuric sulfate ciples of the method may be found in Jirka and digestion solution: To approx 700 mL deminer­ Carter (1975). alized water, add 10.216 g K2Cr2O7 and 33.0 g HgSO4. CAUTION: Hazardous. Slowly, and 3. Interferences with constant stirring, add 167 mL concen­ 3.1 Reducing substances such as ferrous trated H2SO4 (sp gr 1.84). Mix until dissolved. iron and chloride interfere, because they are ox­ After the solution cools, dilute to 1 L with idized by dichromate in acid solution. Chlorides demineralized water. constitute the largest and most common in­ 5.4 Silver sulfate solution: Dissolve 22 g terference, with 1 mg/L CH equivalent to 0.226 Ag2SO4 in a 9-pound bottle of concentrated mg/L COD. To eliminate chloride interference H2SO4 (sp gr 1.84). as great as 2,000 mg/L, add mercuric sulfate to 5.5 Sulfuric acid, concentrated (sp gr 1.84). the acid-dichromate digestion solution. 3.2 Chromium(III) interferes. One milligram 6. Procedure per liter is equivalent to 0.719 mg/L COD. 6.1 Heat the ampules at 500 °C for 6 h, and Levels great enough to have significant effect cool. on the accuracy are unlikely in natural water 6.2 Pipet 2.5 mL of a well-mixed sample in­ samples. to an ampule. 3.3 Ferric iron concentrations less than 5000 6.3 Prepare a blank and sufficient standards mg/L do not interfere. containing from 10 to 500 mg/L COD using potassium acid phthalate standard solution II. 4. Apparatus Pipet 2.5 mL of each into ampules. 4.1 Ampules, glass, 10-mL capacity. 6.4 Add 1.5 mL potassium dichromate- 4.2 Centrifuge, Sorvall SS-3 Automatic mercuric sulfate digestion solution to each am­ Superspeed or equivalent. pule (NOTE 1). 4.3 Spectrometer for use at 600 nm: Refer to NOTE 1. Protective eyeglasses and clothing are the manufacturer's manual to optimize instrument. mandatory for this entire procedure, because 357 358 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS sulfuric acid and potassium dichromate solutions 7. Calculations at high temperatures are especially hazardous. Determine the milligrams per liter of COD in 6.5 Add 3.5 mL silver sulfate solution to each sample from a plot of absorbances of each ampule. standards. 6.6 Heat-seal the ampules and shake vigorously. 8. Report 6.7 Heat the ampules in an oven at 150°C Report oxygen demand, chemical (COD), total for 2 h. (00340), concentrations as follows: less than 10 6.S Cool the ampules to room temperature mg/L, as <10 mg/L; 10 mg/L and above, two in a cold-water bath. significant figures. 6.9 Centrifuge the solutions at 5,000 rpm for 15 min. 9. Precision 6.10 Set the spectrophot&meter at 600 nm and For potassium acid phthalate standards, the adjust the absorbance to 0.000 with the precision for a single operator expressed in digested blank. terms of the percent relative standard deviation 6.11 Individually transfer each standard and is as follows: sample to the sample cuvette, preferably using an automated flow-through cell, and read and Mean Relative standard deviation record each absorbance value. Care must be ("8/D _____(percent)_____ taken not to disturb any precipitate when pour­ 50 14 ing the sample into the cuvette (NOTE 2). 400 2 NOTE 2. A Technicon AutoAnalyzer system, consisting of a sampler, proportioning pump, cartridge manifold, colorimeter, recorder, and Reference printer, may be used in place of the spectro- Jirka, A. M., and Carter, M. J., 1975, Micro semiautomated photometer to measure the absorbance of the analysis of surface and wastewaters for chemical oxygen digested solution (Jirka and Carter, 1975). Steps demand: Analytical Chemistry, v. 47, no. 8t p. 6.2 to 6.9 remain unchanged. 1397-1402. Oxygen demand, chemical (COD), titrimetric, dichromate oxidation

Parameters and Codes: Oxygen demand, chemical, total, 0.025A/ dichromate, 1-3562-85 (COD in mg/L): 00335 Oxygen demand, chemical, total, 0.25N dichromate, 1-3560-85 (COD in mg/L): 00340 Oxygen demand, chemical, total-in-bottom-materials, dry wt, 1-5560-85 (COD in mg/kg): 00339

1. Application equivalent to 0.226 mg/L COD. To eliminate 1.1 This method may be used to analyze chloride interference, add mercuric sulfate to natural water and industrial waste containing the sample to form a soluble mercuric chloride more than 50 mg/L chemical oxygen demand complex. Nitrite interference may be eliminated (COD) and less than 2,000 mg/L of chloride. by incorporating in the standard dichromate Samples containing less than 50 mg/L COD solution 10 mg of sulfamic acid for each need to be analyzed as directed in paragraph milligram of nitrite in the reflux flask. 6.10. COD values for samples containing more than 2,000 mg/L of chloride need to be corrected 4. Apparatus as indicated in paragraph 6.11. 4.1 Reflux apparatus, consisting of 500-mL 1.2 This method may be used to analyze Erlenmeyer flask and water-cooled condenser, samples of bottom material containing more with ground-glass joints and made of heat- than 100 mg/kg chemical oxygen demand resistant glass. (COD). Samples containing less than 1,000 4.2 Hotplate or heating mantle. mg/kg COD need to be analyzed as directed in paragraph 6.10. 5. Reagents 1.3 Bottom material may be analyzed by the 5.1 Ferrous ammonium sulfate standard procedure after it has been prepared as directed solution /, appprox 0.25CW: Dissolve 98.0 g in method P-0810 or P-0811. FeSO4-(NH4)2SO4-6H2O in demineralized water. Add 20 mL concentrated H2SO4 (sp gr 2. Summary of method 1.84), cool, and dilute to 1 L with demineralized 2.1 Organic and other oxidizable material is water. To standardize: Dilute 25.0 mL standard oxidized by refluxing with standard atid-dichro- 0.2500AT K2Cr2O7 solution to 250 mL. Add 20 mate solution in the presence of silver sulfate mL concentrated H2SO4 (sp gr 1.84) and cool. catalyst. The excess dichromate is titrated with Titrate with the ferrous ammonium sulfate solu­ standard ferrous ammonium sulfate, using or- tion, using 8 to 10 drops ferroin indicator. Com­ thophenanthroline ferrous complex as indicator. pute normality of the ferrous ammonium sulfate 2.2 For additional information, see Ameri­ standard solution to four decimal places. The can Society for Testing and Materials, (1984). solution must be standardized daily or before use. 3. Interferences 5.2 Ferrous ammonium sulfate standard Reducing substances such as ferrous iron, solution //, 0.025AT: Dilute 100 mL of ferrous nitrites, and chlorides interfere, because they ammonium sulfate standard solution I to 1,000 are oxidized. Chlorides constitute by far the mL with demineralized water. The normality of greatest and most common interference, being this solution is dependent upon the standard­ quantitatively oxidized by dichromate in acid ized normality of solution I. solution. One milligram of chloride per liter is 5.3 Mercuric sulfate, powdered HgSO4. 359 360 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.4 Orthophenanthroline ferrous sulfate (fer- sulfate standard solution I, using 8 to 10 drops roin) indicator solution: Dissolve 1.48 g ferroin indicator solution. The end point is a l,10-(ortho)-phenanthroline monohydrate and sharp change from blue green to reddish brown. 0.70 g FeSO4-7H2O in 100 mL water. The 6.9 A demineralized-water blank is carried prepared indicator is available commercially. through all steps of the procedure with each 5.5 Potassium dichromate standard solution group of samples. I, 0.2500M Dissolve 12.2588 g K2Cr2O7 6.10 Samples containing less than 50 mg/L primary standard, dried for 2 h at 110°C, in COD or 1,000 mg/kg COD should be reanalyzed, demineralized water and dilute to 1,000 mL. using 0.025AT solutions of potassium dichromate 5.6 Potassium dichromate standard solution and ferrous ammonium sulfate. A sample size II, 0.0250M Dilute 100 mL of potassium should be selected so that no more than half the dichromate standard solution I to 1,000 mL dichromate is reduced. with demineralized water. 6.11 To determine COD on samples contain­ 5.7 Silver sulfate, powder, Ag2SO4. ing more than 2,000 mg/L of chloride, the follow­ 5.8 Sulfamic acid, crystals. ing treatment should be used (Burns and 5.9 Sulfuric acid, concentrated (sp gr 1.84). Marshall, 1965). Add 10 mg HgSO4 for each milligram of chloride ion in the sample aliquot. 6. Procedure Prepare a series of chloride solutions contain­ 6.1 Follow instructions in paragraph 6.1.1 ing from 2,000 to 20,000 mg/L with the concen­ for natural waters and industrial wastes, and tration interval not exceeding 4,000 mg/L, and in paragraph 6.1.2 for bottom materials. add 10 mg HgSO4 to each solution for each 6.1.1 Pipet 50.0 mL of a well-mixed sample or milligram of chloride ion present. Determine the of a smaller volume diluted to 50.0 mL into the COD of the sample and chloride solution, start­ reflux flask. ing with paragraph 6.2. Plot the COD values ob­ 6.1.2 Weigh, to the nearest milligram, an tained versus milligrams per liter chloride. From amount of wet sample (1.0 g max) that will con­ this curve, COD values may be obtained for any sume approx one-half of the 0.2500JV K2Cr2O7 desired chloride concentration. This value is solution added in paragraph 6.5. Transfer the subtracted as a correction factor to obtain the sample to the reflux flask and add 50 mL COD value of a sample. demineralized water. 6.2 Add slowly, over a period of 2 to 3 min, 7. Calculations 1 g HgSO4; allow to stand 5 min, swirling fre­ 7.1 For natural waters and industrial wastes quently. not requiring chloride correction: 6.3 Add 1 g Ag2SO4 and a few glass beads that have been ignited at 600 °C for 1 h. (A-B)N X 8,000 6.4 Cool in ice water and add 75 mL concen­ COD (mg/L) = trated H2SO4 (sp gr 1.84) slowly enough, with sample mixing, to prevent appreciable solution heating. 6.5 Add 25.0 mL 0.2500AT K2Cr2O7 solution 7.2 For natural waters and industrial wastes and mix thoroughly by swirling (NOTE 1). requiring chloride correction: NOTE 1. If contents are not well mixed, superheating may result, and the contents of (A-B)N X 8,000 the flask may be expelled from the open end of COD (mg/L) -C X 1.20 the condenser. [ mL sample 6.6 Attach flask to condenser, start water flow, and reflux for 2 h. where 6.7 Allow flask to cool and wash condenser with 25 mL demineralized water. COD = chemical oxygen demand from 6.8 Dilute to 300 mL with demineralized dichromate, water, cool to room temperature, and titrate the A = amount of ferrous ammonium excess dichromate with ferrous ammonium sulfate for blank, milliliters, METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 361

B = amount of ferrous ammonium A amount of ferrous ammonium sulfate for sulfate for sample, milliliters, blank, milliliters, N = normality ferrous ammonium B = amount of ferrous ammonium sulfate for sulfate, sample, milliliters, C = chloride-correction value from graph and of chloride concentration versus N = normality ferrous ammonium sulfate. COD, and 1.20 empirical compensation factor. 8. Report 8.1 Report COD, total, 0.025AT dichromate 7.3 Compute the dry weight of the bottom- (00335), as follows: less than 50 mg/L, whole material samples as follows: numbers. (100-M) 8.2 Report COD, total, 0.257V dichromate Sample, dry weight (g) = W- 100 (00340), as follows: 50 mg/L and above, two significant figures. where 8.3 Report COD, total-in-bottom-material, W = wet weight of the sample, grams, dry-weight (00339), as follows: less than 10,000 and mg/kg, to the nearest 100 mg/kg; 10,000 mg/kg M = percentage moisture. and above, two significant figures. 7.4 Determine the chemical oxygen demand in each bottom-material sample as follows 9. Precision (NOTE 2): Precision data are not available for this NOTE 2. Most bottom-material samples con­ method. tain low concentrations of chloride; therefore, a chloride correction is not necessary. References (A-B)N X 8,000 COD (mg/kg) = American Society for Testing and Materials, 1984, Annual sample, dry weight (g) book of ASTM standards, section 11. water: Phila­ delphia, v. 11.01, p. 62-8. where Burns, E. R., and Marshall, CM 1965, Correction for chloride COD = chemical oxygen demand from interference in the chemical oxygen demand test: Water dichromate, Pollution Control Federation Journal, v. 37, p. 1716-21.

pH, electrometric, glass-electrode

Parameters and Codes: pH lab, 1-1586-85 (units): 00403 pH lab, automated, 1-2587-85 (units): 00403

1. Application 4.3 A new glass electrode or one that has This method may be used to determine the dried completely may require several hours of pH of any natural or treated water and any in­ soaking in water or buffer solution before it pro­ dustrial or other wastewater. duces stable, reliable readings. The tip of the glass electrode must be kept immersed in water 2. Summary of method when not in use. Although the glass tip is 2.1 See the introduction to electrometry in reasonably durable, it can be damaged, and this chapter for the principles of pH-meter should never be cleaned or wiped with an operation. See also Barnes (1964), Bates (1964), abrasive or dirty tissue or cloth. and Willard and others (1965). 2.2 This procedure may be automated with 5. Reagents commercially available instrumentation. Standard buffer solutions, pH 4.00, 7.00, and 9.00: These buffers should cover the range of pH 3. Interferences of the samples to be measured. If samples of pH 3.1 The determination is not affected by the less than 4.00 or greater than 9.00 are to be presence of color or turbidity, or of organic or analyzed, additional buffers will be required. colloidal material. Oxidizing and reducing sub­ Ready-made buffer reagents are satisfactory. stances do not impair the accuracy of method. 3.2 The pH measurement is temperature 6. Procedure dependent, and a significant error results if the 6.1 After an appropriate warmup period, temperatures of the buffers and samples differ standardize the instrument with the buffer solu­ appreciably. However, a variation of less than tions, bracketing the pH values of the samples. 5 °C has no significant effect except in the most Samples and buffers must be at the same exacting work. temperature. 3.3 For samples having abnormally high 6.2 With a minimum of aeration or agitation, sodium levels, corrections may be necessary. measure the pH of samples hi accordance with This correction varies with the type of elec­ the manufacturer's instructions. trodes used; hence, see the manufacturer's in­ structions for the necessary computations. 7. Calculations The pH is read directly from the meter. 4. Apparatus 4.1 pH meter, with glass and reference elec­ 8. Report trodes or combination pH electrode. Report pH values (00403) to the nearest 0.1 4.2 Several types of pH meters are available, pH unit. including digital and expanded-scale models. Unless a different type is needed for special pur­ 9. Precision poses, an ordinary laboratory, line-operated, pH 9.1 Precision for pH for five of the 36 meter—capable of a reproducibility of 0.05 of a samples expressed hi terms of standard devia­ pH unit—is adequate. tion is as follows:

363 364 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Number of Mean Relative standard deviation deviations of 0.05 and 0.03 pH units, laboratories (pH units) ____(pH units)____ respectively. 27 6.21 0.26 59 7.14 .32 33 7.52 .15 References 48 8.00 .21 60 8.54 .15 Barnes, Ivan, 1964, Field measurement of alkalinity and pH: US Geological Survey Water- Supply Paper 1535-H, 17 p. 9.2 Using automated instrumentation, Bates, R. G., 1964, Determination of pH—theory and prac­ tice: New York, John Wiley and Sons, 435 p. analysis of two test samples by a single labor­ Willard, H. H., Merritt, L. L., Jr., and Dean, J. A., 1974, In­ atory for 25 replicates of each resulted in mean strumental methods of analysis (5th ed): New York, D. values of 7.58 and 8.07 pH units and standard Van Nostrand, 860 p. Phosphorus, colorimetric, phosphomolybdate

Parameter and Code: Phosphorus, dissolved, 1-1600-85 (mg/L as P): 00666

1. Application silica is somewhat dependent on the reagents; This method may be used to analyze most therefore, an appropriate silica correction water and wastewater containing between 0.02 should be determined for each batch of and 0.4 mg/L of dissolved phosphorus. Samples reagents. Nitrite interferes, but can be oxidized containing greater concentrations need to be to nitrate with hydrogen peroxide before diluted. analysis. Residual chlorine must be removed by boiling the sample. 2. Summary of method 3.2 Mercuric chloride interferes when the 2.1 As far as is known, the phosphomolyb­ chloride concentration is less than 50 mg/L. date method is specific for the orthophosphate Mercuric chloride-preserved samples are for­ form of phosphorus. Weak tests are reported tified with a minimum of 85 mg/L NaCl to over­ with pyrophosphate and polyphosphate, but come this interference. these positive tests may well result from ortho- 3.3 Arsenic as arsenate (AsOj3) produces a phosphate contamination of the material. color similar to that of phosphate (Murphy and 2.2 Acid hydrolyzable and organic forms of Riley, 1962) and may cause a positive inter­ phosphorus are decomposed to orthophosphate ference. Arsenic concentrations up to 100 jig/L by sulfuric acid-ammonium persulfate diges­ do not i interfere. Greater concentrations were tion. Orthophosphate is then converted to not investigated. phosphomolybdate by acidified ammonium molybdate reagent: 4. Apparatus Spectrometer for use at 700 or 882 nm. H3PO4 + 12(NH4)2MoO4 5. Reagents (NH4)3PO4-12MoO3 12H2O 5.1 Ammonium persulfate, (NH4)2S2O8. 5.2 Antimony tartrate-ammordum molybdate 2.3 When phosphomolybdate is reduced solution: Dissolve 0.13 g antimony potassium with ascorbic acid in the presence of antimony tartrate, K(SbO)C4H4O6a/2H2O, in about 700 mL (Murphy and Riley, 1962), an intense blue com­ demineralized water contained in a 1-L volu­ plex is developed that absorbs light at 882 nm. metric flask. Add 5.6 g ammonium molybdate, The reduction is not instantaneous, nor is the (NH4)6Mo7O24-4H2O, and shake flask until dis­ developed blue color stable. The full color solved. Cautiously add 70 mL concentrated develops in 6 to 10 min and fades gradually H2SO4 (sp gr 1.84) while swirling the contents thereafter. of the flask Cool and dilute to volume. Mix thoroughly by repeated inversion and swirling. 3. Interferences This solution is stable for at least 1 year if stored 3.1 Barium, lead, and silver interfere by in a polyethylene bottle away from heat. forming a precipitate. Silica produces a pale- 5.3 Combined reagent solution: Dissolve 0.50 blue color that is additive to the phosphate col­ g ascorbic acid in 100 mL antimony tartrate-am- or and may require correction. The effect of monium molybdate solution. This reagent is 365 366 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS stable for at least 1 week if stored at 4 °C; other­ 6.5 Add 10 mL combined reagent solution wise prepare fresh daily. to each sample, blank, and standard, and mix. 5.4 Phenolphthalein indicator solution, 0.5 6.6 After 10 min, measure absorbance of g/100 mL: Dissolve 0.5 g phenolphthalein in 100 each sample and standard against that of the mL 50-percent ethanol. blank at either 882 or 700 nm. 5.5 Phosphate standard solution I, 1.00 mL = 0.050 mg P: Dissolve 0.2197 g KH2PO4, 7. Calculations dried overnight over H2SO4, in demineralized 7.1 Determine the milligrams of phosphorus water and dilute to 1,000 mL. in each sample from a plot of absorbances of 5.6 Phosphate standard solution II, 1.00 standards. mL = 0.001 mg P: Dilute 20.0 mL phosphate 7.2 Determine the phosphorus concentra­ standard solution I to 1,000 mL with deminer­ tion in milligrams per liter as follows: alized water. 5.7 Sodium hydroxide, 3M: Carefully, with 1,000 cooling, dissolve 120 g NaOH in demineralized P in mg/L = X mg P in sample water and dilute to 1 L. mL sample 5.8 Sulfuric acid, SM: Cautiously, add slow­ ly, with constant stirring and cooling, 330 mL 8. Report concentrated H2SO4 (sp gr 1.84) to 600 mL de- Report phosphorus, dissolved (00666), concen­ mineralized water and dilute to 1 L. trations as follows: less than 1.0 mg/L, two 5.9 Sulfuric acid, 0.25M: Cautiously, add decimals; 1.0 mg/L and above, two significant slowly, with constant stirring and cooling, 14 figures. mL concentrated H2SO4 (sp gr 1.84) to demin­ eralized water and dilute to 1 L. 9. Precision 9.1 The standard deviation for dissolved 6. Procedure phosphorus within the range of 0.138 to 3.14 6.1 Pipet a volume of sample containing less mg/L for 21 samples was found to be independ­ than 0.020 mg P (50.0 mL max) into a 125-mL ent of concentration. The 95-percent confidence Erlenmeyer flask, and adjust the volume to 50.0 interval for the average standard deviation of mL. 0.272 mg/L ranged from 0.252 to 0.296 mg/L. 6.2 Prepare a blank and sufficient stand­ 9.2 Precision for dissolved phosphorus for ards, and adjust the volume of each to 50.0 mL six of the 21 samples expressed in terms of the (NOTE 1). percent relative standard deviation is as follows: NOTE 1. If the samples were preserved with Number of Mean Relative standard deviation mercuric chloride fortified with sodium chloride, laboratories (mg/L) _____(percent)_____ add an equivalent amount to the blank and 13 0.138 48 standards. 15 .573 27 6.3 Add 1.0 mL 6M H2SO4 and 0.4 g 14 .867 5 16 .887 49 (NH4)2S2Og. Boil gently on a hotplate until the 18 1.52 30 volume is reduced to about 10 mL. 15 3.20 5 6.4 Cool. Add 2 drops phenolphthalein in­ dicator solution and neutralize with 3MNaOH, and then carefully add 0.25M H2SO4 until the Reference pink color just disappears. Transfer to a 50-mL Murphy. J., and Riley, J. P., 1962, A modified single-solution volumetric flask and dilute to the mark with de- method for the determination of phosphate in natural mineralized water. waters: Analytica Chemica Acta, v. 27, p. 31-6. Phosphorus, colorimetric, phosphomolybdate, automated-segmented flow

Parameters and Codes: Phosphorus, dissolved, 1-2600-85 (mg/L as P): 00666 Phosphorus, total, 1-4600-85 (mg/L as P): 00665 Phosphorus, total-in-bottom-material, dry wt, 1-6600-85 (mg/kg as P): 00668

1. Application samples to reduce the hydrogen-ion concentra­ 1.1 This method may be used to analyze most tions of all samples. water, wastewater, brines, and water-suspended 3.2 Barium, lead, and silver interfere by sediment containing from 0.01 to 1.0 mg/L of forming a phosphate precipitate, but the effect phosphorus. Samples containing greater con­ is usually negligible in natural waters. The inter­ centrations need to be diluted. ference from silica, which forms a pale-blue com­ 1.2 This method may be used to analyze bot­ plex, is small and can be considered negligible. tom material containing from 40 to 4,000 mg/kg Nitrite interferes, but can be oxidized to nitrate of phosphorus. This range may be extended by with hydrogen peroxide before analysis. using a 0.1-g subsample rather than the 1-g sub- Residual chlorine must be removed by boiling sample specified. the sample. 3.3 Arsenic as arsenate (AsOj3) produces a 2. Summary of method color similar to that of phosphate (Murphy and 2.1 All forms of phosphorus, including Riley, 1962) and may cause a positive inter­ organic phosphorus, are converted to ortho- ference. Arsenic concentrations as much as 100 phosphate by an acid-persulfate digestion. jtg/L do not interfere. Greater concentrations 2.2 Orthophosphate ion reacts with ammon­ were not investigated. ium molybdate in acidic solution to form phos- phomolybdic acid, which, upon reduction with 4. Apparatus ascorbic acid, produces an intensely colored blue 4.1 Autoclave. complex. Antimony potassium tartrate is added 4.2 Centrifuge. to increase the rate of reduction (Murphy and 4.3 Centrifuge tubes, 50-mL capacity. Riley, 1962; Gales and others, 1966). 4.4 Glass tubes with plastic caps, dispos­ 2.3 Mercuric chloride-preserved water able, 18X150 mm. samples and water-suspended sediment mix­ 4.5 Technicon AutoAnalyzer //, consisting tures are fortified with a minimum of 85 mg/L of sampler, cartridge manifold, proportioning NaCl to overcome the interference from mer­ pump, colorimeter, voltage stabilizer, recorder, cury in the analysis. and printer. 2.4 Digested and centrifuged bottom-mate­ 4.6 With this equipment the following rial samples are diluted to reduce the acid and operating conditions have been found satisfac­ phosphorus concentrations before final analysis. tory for the range from 0.01 to 1.0 mg/L P: Absorption cell ——— 50 mm 3. Interferences Wavelength ————— 880 nm or 660 nm 3.1 The color of the molybdate blue complex Cam —————————— 40/h (5/1) is strongly affected by pH. The method incor­ Heating-bath tempera­ porates a dilution step for bottom-material ture ————————— 37.5 °C 367 368 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5. Reagents 5.10 Potassium persulfate solution, 4 g/L: 5.1 Ammonium molybdate solution, 35,6 Dissolve 4.0 g K2S2O8 in demineralized water g/L: Dissolve 40 g ammonium molybdate and dilute to 1 L. (NH4)6Mo7O24-4H2O in 800 mL demineralized 5.11 Sulfuric acid, concentrated (sp gr 1.84). water and dilute to 1 L. 5.12 Sulfuric acid, 2.45M: Cautiously, add 5.2 Ascorbic acid solution, 18 g/L: Dissolve slowly, with constant stirring and cooling, 136 18 g ascorbic acid (C6H8O6) in 800 mL demin­ mL concentrated sulfuric acid (sp gr 1.84) to 800 eralized water and dilute to 1 L. Keep in a dark mL demineralized water and dilute to 1 L with bottle and refrigerate. The solution is stable for demineralized water. 1 week. 5.13 Sulfuric acid, 0.45M: Cautiously, add 5.3 Antimony potassium tartrate solution, slowly, with constant stirring and cooling, 25.2 3 g/L: Dissolve 3.0 g antimony potassium tar­ mL concentrated sulfuric acid (sp gr 1.84) to 800 trate K(SbO)C4H4O6-V6H2O in 800 mL demin­ mL demineralized water and dilute to 1 L with eralized water and dilute to 1 L. demineralized water. 5.4 Combined working reagent: Combine 5.14 Sulfuric acid-persulfate reagent, (1 + 1): reagents in order and volumes listed below. This Mix equal volumes of 0.45M sulfuric acid and reagent is stable for about 8 h. potassium persulfate solution. Sulfuric acid, 2.45M - 50 mL 5.15 Water diluent: Dissolve 20g NaCl in 800 Ammonium molybdate mL demineralized water. Add 2.0 ml. Levor V solution ————— 15 mL and dilute to 1L with demineralized water. Ascorbic acid solution 30 mL Antimony potassium 6. Procedure tartrate solution — 5 mL 6.1 Follow instructions in paragraphs 6.1.1 5.5 Levor V solution or equivalent. through 6.1.4 for water or water-suspended sedi­ 5.6 Phosphate standard solution I, 1.00 ment and in paragraphs 6.1.5 through 6.1.12 for mL = 0.100 mg P: Dissolve 0.4394 g KH2PO4, bottom material. dried overnight over concentrated H2SO4 (sp gr 6.1.1 Pipet a volume of well-mixed sample con­ 1.84), in demineralized water and dilute to 1,000 taining less than 0.01 mg total P (10.0 mL max) mL. into a disposable glass tube, and adjust the 5.7 Phosphate standard solution II, 1.00 volume to 10.0 mL. mL = 0.010 mg P: Dilute 100.0 mL phosphate 6.1.2 Pipet 10.0 mL of blank and each work­ standard solution I to 1,000 mL with deminer­ ing standard into disposable glass tubes. alized water. 6.1.3 Add 4.0 mL sulfuric acid-persulfate 5.8 Phosphate working standards: Prepare reagent. a blank and 200 mL each of a series of working 6.1.4 Place plastic caps gently on top of tubes standards by appropriate quantitative dilution but do not push down. Autoclave for 30 min at of phosphate standard solution II with demin­ 15 Ibs pressure. Cool and filter those samples eralized water. Dissolve 10 mg mercuric chloride containing sediment through a 0.45-jim mem­ and 120 mg sodium chloride in each working brane filter. Proceed to paragraph 6.2. standard. For example: 6.1.5 Accurately weigh a portion of as- received sample having a dry weight of approx Orthophosphate-phosphorus 1 g. The sample must first be prepared as Phosphate standard solution II concentration (mo/L) directed in method P-0810. Transfer the weighed sample to a 50-mL centrifuge tube and 0.0 0.00 1.0 .05 add 10 mL demineralized water. 2.0 .10 6.1.6 On a separate portion, determine the dry 5.0 .25 weight of the sample (method P-0590). 10 .50 20 1.00 6.1.7 Add 1.0 mL concentrated H2SO4 and 1.0 g potassium persulfate to each centrifuge tube. 5.9 Potassium persulfate, crystals. 6.1.8 Autoclave for 30 min at 15 psi pressure. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 369 6.1.9 Centrifuge for 5 to 10 min at 5,000 rpm. subsequent sample trays. Fill remainder of each 6.1.10 Transfer the supernatant solution to a tray with unknown samples. 200-mL volumetric flask, taking care not to 6.6 Begin analysis. When the peak from the disturb the residue in the bottom of the cen­ most concentrated standard appears on the trifuge tube. recorder, adjust the STD CAL control until the 6.1.11 Wash the residue several times with de- flat portion of the curve reads full scale. mineralized water, adding the washings to the volumetric flask. Dilute to 200 mL with demin- 7. Calculations eralized water. 7.1 Prepare an analytical curve by plotting 6.1.12 Pipet 5.0 mL of sample, into a 100-mL the height of each standard peak versus its volumetric flask and dilute to volume with de- respective orthophosphate-phosphorus concen­ mineralized water. Proceed to paragraph 6.2 tration. (NOTE 1). 7.2 Compute the concentration of dissolved NOTE 1. Use blank and standards as prepared or total phosphorus in each sample by compar­ in paragraphs 6.1.2 through 6.1.4. ing its peak height to the analytical curve. Any 6.2 Set up manifold (fig. 37). baseline drift that may occur must be taken in­ 6.3 Allow colorimeter, recorder, and heating to account when computing the height of a sam­ bath to warm for at least 30 min or until the ple or standard peak. temperature of the heating bath is 37.5 °C. 7.3 Compute total phosphorus concentra­ tions in each bottom-material sample as follows: 6.4 Adjust the baseline to read zero scale divisions on the recorder for all reagents, but P 20 with demineralized water in the sample line. Phosphorus (mg/kg) = — X — X 1,000 6.5 Place a complete set of standards and a blank in the first positions of the first sample where tray, beginning with the most concentrated P — concentration of phosphorus, milligrams standard. Place individual standards of differ­ per liter, in the sample, ing concentrations in approximately every and eighth position of the remainder of this and W — dry weight, grams, of the sample.

no. Air 573-03 0.030in 5-turn coils 0.32mL/mln (Bflinnnh mnmn ^ f 0.0 30 in Water diluent / i t i 0.32mL/mln ; He ating bath ^ • 37.5°C 0.035ln 3 i r Sampler 4 0.42 mL /min 40/h 5/1 cam Cotlorimeter 0.030ln Combined reapent 88 Onm* Waste 0.32mL/mln 15-mm cell^r To sai npl er 4 0.073in Waeh solution i th -* wat 2.00mL/mln T rec•PiCacle 0.040in Waste V ^ 0.60mL/min I Recorder Pr<^portioning pump

Alternatively 660 nm Figure 37.—Phosphorus, phosphomolybdate manifold 370 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 8. Report 9.2 Precision for dissolved phosphorus for 8.1 Report phosphorus, dissolved (00666), four of the 20 samples expressed in terms of the and total (00665), concentrations as follows: less percent relative standard deviation is as follows: than 1 mg/L, two decimals; 1 mg/L and above, Number of Mean Relative standard deviation two significant figures. laboratories _____(percent)_____ 8.2 Report phosphorus, total-in-bottom- 3 0.183 12 material (00668), in milligrams per kilogram, to 13 .572 8 two significant figures. 18 1.411 9 15 3.59 19 9. Precision 9.3 It is estimated that the percent relative 9.1 Precision for dissolved phosphorus for standard deviation for total phosphorus and for 20 samples within the range of 0.183 to 3.59 total phosphorus in bottom material will be mg/L may be expressed as follows: , greater than that reported for dissolved phos­ phorus.

= 0.189 X -0.062 References where Gales, M. E., Jr., Julian, E. C., and Kroner, R. C., 1966, ST = overall precision, milligrams per liter, Method for quantitative determination of total phos­ and phorus in water: American Water Works Association Journal, v. 58, p. 1363-8. X sss concentration of phosphorus, milligrams Murphy, J.f and Riley, J. P., 1962, A modified single-solution per liter. method for the determination of phosphate in natural The correlation coefficient is 0.9260. waters: Analytica Chimica Acta, v. 27, p. 31-6. Phosphorus, colorimetric, phosphomolybdate, automated-discrete

Parameters and Codes: Phosphorus, dissolved, 1-2599-85 (mg/L as P): 00666 Phosphorus, total, 1-4599-85 (mg/L as P): 00665

1. Application A 0.1-mg/L P spike is dispensed into the four This method may be used to analyze water, leading wash tubes with the color reagent. The wastewater, water-suspended sediment, and resulting blue color then coats the flow cell prior brines containing from 0.01 to 2.0 mg/L phos­ to the introduction of the working standards. By phorus. Samples containing concentrations this action, the high bias is effectively greater than 2.0 mg/L need to be diluted. eliminated.

2. Summary of method 4. Apparatus 2.1 All forms of phosphorus, including 4.1 Discrete chemical analyzer system, organic phosphorus, are converted to ortho- American Monitor IQAS or equivalent. phosphate by an acid-persulfate digestion. 4.2 With this equipment, the following 2.2 Orthophosphate ion reacts with am­ operating conditions have been found monium molybdate in acidic solution to form satisfactory: phosphomolybdic acid, which upon reduction Wavelength —— 880 nm with ascorbic acid produces an intensely colored Absorption cell 1 cm square, tempera­ blue complex. Antimony potassium tartrate is ture-controlled, flow- added to increase the rate of reduction (Murphy through quartz and Riley, 1962; Gales and others, 1966). cuvette 2.3 Mercuric chloride-preserved samples are Reaction tem­ fortified with a minimum of 85 mg/L NaCl to perature —— 37 °C overcome the interference from mercury in the Sample volume 0.400 mL with 0.050 analysis. mL diluent (NOTE 1) 3. Interferences Reagent 3.1 Barium, lead, and silver interfere by volumes —— 0.25 mL color reagent forming a precipitate. The interference from and 0.80 mL demin- silica, which forms a pale-blue complex, is slight eralized water and can be considered negligible. Nitrite in­ (NOTE 1) terferes, but can be oxidized to nitrate with NOTE 1. Sample-to-diluent ratio and reagent hydrogen peroxide before analysis. Residual volumes must be optimized for each instrument chlorine must be removed by boiling the sample. according to manufacturer's specifications. 3.2 Arsenic as arsenate (AsOj3) produces a 4.3 Autoclave. color similar to that of (Murphy and Riley, 1962) 4.4 Glass tubes with plastic caps, disposable, and may cause a positive interference Arsenic 18 by 150 mm. concentrations as much as 100 jig/L do not inter­ fere. Greater concentrations were not investigated. 5. Reagents 3.3 The blue color produced will coat the flow 5.1 Ammonium molybdate solution, 35.6 cell, causing a small but significant high bias. g/L: Dissolve 40 g ammonium molybdate, 371 372 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS (NH4)6Mo7O24'4H20, in 800 mL demineralized 5.11 Sulfuric add, 0.45M; Cautiously, add slow­ water and dilute to 1L. ly, with constant stirring and cooling, 25.2 mL 5.2 Antimony potassium tartrate solution, 3 concentrated sulfuric acid (sp gr 1.84) to 800 mL g/L: Dissolve 3.0 g antimony potassium tartrate, demineralized water and dilute to 1 L with de- RfSbOJC^Og-VfeHgO, in 800 mL demineralized mineralized water. water and dilute to 1 L. 5.12 Sulfuric acid-persulfate reagent, (1 + 1): 5.3 Ascorbic acid solution, 18 g/L: Dissolve Mix equal volumes of 0.45M sulfuric acid and 18 g ascorbic acid (C6H8O6) in 800 mL demin­ potassium persulfate solution. eralized water and dilute to 1 L. 5.4 Combined working reagent: Combine 6. Procedure reagents in order and volumes listed below. This 6.1 Pipet a volume of well-mixed sample con­ reagent is stable for about 8 h: taining less than 0.02 mg total P (10.0 mL max) Sulfuric acid, 2.45Af ————— 50 mL into a disposable glass tube, and adjust the Ammonium molybdate solution 15 mL volume to 10.0 mL. Ascorbic acid solution ———— 30 mL 6.2 Pipet 10.0 mL of blank and each working Antimony potassium tartrate standard into disposable glass tubes. solution ——————————— 5 mL 6.3 Add 4.0 mL sulfuric acid-persulfate 5.5 Phosphate standard solution 1, 1.00 mL = reagent. 1.00 mg P: Dissolve 4.394 g KH2P04, dried over­ 6.4 Place plastic caps gently on top of tubes night over concentrated H2SO4 (sp gr 1.84), in de- but do not push down. Autoclave for 30 min at mineralized water and dilute to 1,000 mL. 15 Ibs pressure Cool and filter those samples con­ 5.6 Phosphate standard solution II, 1.00 mL = taining sediment through a 0.45-/xm membrane 0.05 mg P: Dilute 50.0 mL phosphate standard filter. solution I to 1,000 mL with demineralized water. 6.5 Set up analyzer and computer-card assign­ 5.7 Phosphate working standards: Prepare a ments according to manufacturer's instructions. blank and 1,000 mL each of a series of working 6.6 Place standards, beginning with the low* standards by appropriate quantitative dilution est concentrations, in ascending order (computer- of phosphate standard solution II with demin­ calibration curve) in the first five positions on the eralized water. Dissolve 52 mg mercuric chloride sample turntable Place samples and quality- and 600 mg sodium chloride in each working control standards in the remainder of the sam­ standard. For example: ple turntable 6.7 Begin analysis. The cathode-ray tube Standard solution II Ortnophospnate-phosphoms concentration (CRT) will acknowledge the parameter and con­ (mL) (mfl/L) centration range, listing each sample-cup number 0.0 0.00 and the corresponding concentrations calculated 1.0 .05 from the working curve During each run, the 5.0 .25 10.0 .50 CRT display will provide a plot of standards, 20.0 1.00 samples, and list blank and slope calculations. 40.0 2.00 Retain copy of all information obtained from printer. 5.8 Phosphate standard solution III (spike), 1.00 mL = 0.0001 mg P: Dilute 2.0 mL phos­ 7. Calculations phate standard solution II to 1,000 mL with de- Determine the concentration in milligrams per mineralized water. liter of dissolved or total phosphorus in each sam­ 5.9 Potassium persulfate solution, 4 g/L: Dis­ ple from either the CRT display or the printer solve 4.0 g K2S2O8 in demineralized water and output. dilute to 1 L. 5.10 Sulfuric acid, 2.45M Cautiously, add slow­ 8. Report ly, with constant stirring and cooling, 136 mL Report phosphorus, dissolved (00666), and concentrated sulfuric acid (sp gr 1.84) to 800 mL total (00665), concentrations as follows: less than demineralized water and dilute to 1 L with de- 1.0 mg/L, two decimals; 1.0 mg/L and above, two mineralized water. significant figures. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 373 9. Precision References The precision expressed in terms of the stand­ ard deviation and percent relative standard deviation for replicate analysis of reference Gales, M. E., Jr., Julian, E. C., and Kroner, R. C., 1966, materials by a single operator is as follows: Method for quantitative determination of total phos­ phorus in water: American Water Works Association Mean Number of Standard deviation Relative standard deviation (mp/L) replicates ___(mq/L) _____(percent)_____ Journal, v. 58, p. 1363-8. 0.142 27 0.009 6.34 .551 25 .009 1.63 Murphy, J., and Riley, J. P., 1962, A modified single-solu­ .750 25 .009 1.20 tion method for the determination of phosphate hi 1.00 25 .015 1.50 natural waters: Analytica Chimica Acta, v. 27, 1.72 22 .007 .41 2.00 25 .027 1.35 p. 31-6.

Phosphorus, orthophosphate plus hydrolyzable, colorimetric, phosphomolybdate

Parameter and Code: Phosphorus, orthophosphate plus hydrolyzable, dissolved, 1-1602-85 (mg/L as P): 00677

1. Application an appropriate silica correction should be deter­ This method may be used to analyze most mined for each batch of reagents. Nitrite in­ water and wastewater containing between 0.02 terferes, but can be oxidized to nitrate with and 0.4 mg/L of dissolved orthophosphate plus hydrogen peroxide before analysis. Residual hydrolyzable phosphorus. Samples containing chlorine must be removed by boiling the sample. greater concentrations need to be diluted. 3.2 Mercuric chloride interferes when the chloride concentration is less than 50 mg/L. 2. Summary of method Mercuric chloride-preserved samples are for­ 2.1 As far as is known, the phosphomolyb­ tified with a minimum of 85 mg/L NaCl to over­ date method is specific for the orthophosphate come this interference. form of phosphorus. Weak tests are reported 3.3 Arsenic as arsenate (AsO43) produces a with pyrophosphate and polyphosphates, but color similar to that of phosphate (Murphy and these positive tests may well result from or­ Riley, 1962) and may cause a positive interfere. thophosphate contamination of the material. Arsenic concentrations as much as 100 /ig/L do 2.2 Acid hydrolyzable phosphorus is decom­ not interfere. Greater concentrations were not posed to orthophosphate by sulfuric acid diges­ investigated. tion. Orthophosphate is then converted to phosphomolybdate by acidified ammonium 4. Apparatus molybdate reagent: Spectrometer for use at 700 or 882 nm.

H3PO4 + 12(NH4)2MoO4 5. Reagents 5.1 Antimony tartrate-ammonium molybdate (NH4)3PO4-12MoO3 12H2O solution: Dissolve 0.13 g antimony potassium tartrate^ K(SbO)C4H4O6a/2H2O, in about 700 mL 2.3 When phosphomolybdate is reduced demineralized water contained in a 1-L with ascorbic acid in the presence of antimony volumetric flask. Add 5.6 g ammonium molyb­ (Murphy and Riley, 1962), an intense blue com­ date, (NH4)6Mo7O24-4H2O, and shake flask un­ plex is developed that absorbs light at 882 nm. til dissolved. Cautiously, add 70 mL concentrated The reduction is not instantaneous, nor is the H2SO4 (sp gr 1.84) while swirling the contents developed color stable. The full color develops of the flask Cool and dilute to volume. Mix in 6 to 10 min and fades gradually thereafter. thoroughly by repeated inversion and swirling. This solution is stable for at least 1 year if stored 3. Interferences in a polyethylene bottle away from heat. 3.1 Barium, lead, and silver interfere by 5.2 Combined reagent solution: Dissolve 0.50 forming a precipitate. Silica gives a pale-blue g ascorbic acid in 100 mL antimony tartrate- color that is additive to the phosphate color and ammonium molybdate solution. This reagent is may require correction. The effect of silica is stable for at least 1 week if stored at 4°C; other­ somewhat dependent on the reagents; therefore, wise prepare fresh daily. 375 376 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Phenolphthalein indicator solution, 0.5 and then carefully add 0.25M H2SO4 until the g/100 mL: Dissolve 0.5 g phenolphthalein in 100 pink color just disappears. Transfer to a 50-mL mL 50-percent ethanol. volumetric flask and dilute to the mark with de- 5.4 Phosphate standard solution I, 1.00 mineralized water. mL = 0.050 mg P: Dissolve 0.2197 g KH2PO4, 6.5 Add 10 mL combined reagent to each dried overnight over H2SO4, in demineralized sample, blank, and standard, and mix. water and dilute to 1,000 mL. 6.6 After 10 min measure absorbance of 5.5 Phosphate standard solution II, 1.00 each sample and standard against that of the mL = 0.001 mg P: Dilute 20.0 mL phosphate blank at either 882 or 700 nm. standard solution I to 1,000 mL with deminer­ alized water. 7. Calculations 5.6 Sodium hydroxide, 3Af: Carefully, with 7.1 Determine the milligrams of phosphorus cooling, dissolve 120 g NaOH in demineralized in each sample from a plot of absorbances of water and dilute to 1 L. standards. 5.7 Sulfuric acid, 6M: Cautiously, add slow­ 7.2 Determine the phosphorus concentra­ ly, with constant stirring and cooling, 330 mL tion in milligrams per liter as follows: concentrated H2SO4

Parameters and Codes: Phosphorus, orthophosphate plus hydrolyzable, dissolved, 1-2602-85 (mg/L as P): 00677 Phosphorus, orthophosphate plus hydrolyzable, total, 1-4602-85 (mg/L as P): 00678

1. Application 3.2 Mercuric chloride interferes when the This method may be used to analyze most chloride concentration is less than 50 mg/L. water, brines, and water-suspended sediment 3.3 Arsenic as arsenate (AsOj3) produces a containing between 0.01 and 1.0 mg/L combined color similar to that of phosphate (Murphy and acid hydrolyzable and orthophosphate-phos- Riley, 1962) and may cause a positive inter­ phorus. Samples containing greater concentra­ ference. Arsenic concentrations as much as 100 tions need to be diluted. jig/L do not interfere. Greater concentrations were not investigated. 2. Summary of method 2.1 Polyphosphates (P2O7)-4, (P3O10)-5, etc., 4. Apparatus and a few organic phosphorus compounds are 4.1 Autoclave. converted to orthophosphate by an acid 4.2 Technicon AutoAnalyzer II, consisting hydrolysis. of sampler, cartridge manifold, proportioning 2.2 Orthophosphate ion reacts with am­ pump, heating bath, colorimeter, voltage monium molybdate in acidic solution to form stabilizer, recorder, and printer. phosphomolybdic acid, which, upon reduction 4.3 With this equipment the following with ascorbic acid, produces an intensely col­ operating conditions have been found satisfac­ ored blue complex. Antimony potassium tar- tory for the range from 0.01 to 1.0 mg/L com­ trate is added to increase the rate of reduction bined hydrolyzable and orthophosphate- (Murphy and Riley, 1962; Gales and others, phosphorus: 1966). Absorption cell ——— 50 mm 2.3 Mercuric chloride-preserved samples are Wavelength ————— 880 nm or 660 nm fortified with a minimum of 85 mg/L NaCl to Cam —————————— 40/h (5/1) overcome the interference from mercury in the Heating-bath temper­ analysis. ature ———————— 37.5 °C 4.4 Glass tubes with plastic caps, dispos­ 3. Interferences able, 18 X 150 mm. 3.1 Barium, lead, and silver interfere by forming a phosphate precipitate, but the effect 5. Reagents is usually negligible in natural waters. The inter­ 5.1 Ammonium molybdate solution, 35.6 ference from silica, which forms a pale-blue com­ g/L: Dissolve 40 g ammonium molybdate, plex, is slight and can be considered negligible. (NH4)6Mo7O24-4H2O, in 800 mL demineralized Nitrite interferes, but can be oxidized to nitrate water and dilute to 1 L. with hydrogen peroxide before analysis. 5.2 Ascorbic acid solution, 18 g/L: Dissolve Residual chlorine must be removed by boiling 18 g ascorbic acid (C6H8O6) in 800 mL demin­ the sample. eralized water and dilute to 1 L.

377 378 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Antimony potassium tartrate solution, 6. Procedure 3 g/L: Dissolve 3.0 g antimony potassium tar­ 6.1 Pipet a volume of well-mixed sample con­ trate, K(SbO)C4H4O6-1/2H2O, in 800 mL demin- taining less than 0.01 mg combined hydrolyzable eralized water and dilute to 1 L. and orthophosphate-phosphorus (10.0 mL max) 5.4 Combined working reagent: Combine into a disposable glass tube and adjust the reagents in order and volumes listed below. This volume to 10.0 mL. reagent is stable for about 8 h: 6.2 Pipet 10.0 mL of blank and each work­ Sulfuric acid, 2.45M ———— 50 mL ing standard into disposable glass tubes. Ammonium molybdate solu­ 6.3 Add 2.0 mL 0.45M sulfuric acid. tion ————————————— 15 mL 6.4 Place plastic caps gently on top of tubes Ascorbic acid solution —— 30 mL but do not push down. Autoclave for 30 min at Antimony potassium tartrate 15 Ibs pressure. Cool and filter those samples solution ————————— 5 mL containing sediment through a 0.45-/un mem­ 5.5 Levor V solution or equivalent. brane filter. 5.6 Phosphate standard solution I, 1.00 6.5 Set up manifold (fig. 38). mL = 0.100 mg P: Dissolve 0.4394 g KH2PO4, 6.6 Allow colorimeter, recorder, and heating dried overnight over concentrated H2SO4 (sp gr bath to warm for at least 30 min or until the 1.84), in demineralized water and dilute to 1,000 temperature of the heating bath is 37.5 °C. mL. 6.7 Adjust the baseline to read zero scale 5.7 Phosphate standard solution II, 1.00 divisions on the recorder for all reagents, mL = 0.010 mg P: Dilute 100.0 mL phosphate but with demineralized water in the sample standard solution I to 1,000 mL with deminer­ line. alized water. 6.8 Place a complete set of standards and a 5.8 Phosphate working standards: Prepare blank in the first positions of the first sample a blank and 200 mL each of a series of working tray, beginning with the most concentrated standards by appropriate quantitative dilution standard. Place individual standards of differ­ of phosphate standard solution II. Dissolve 10 ing concentrations in approximately every mg mercuric chloride and 120 mg sodium eighth position of the remainder of this and chloride in each working standard. For example: subsequent sample trays. Fill remainder of each tray with unknown samples. Phosphate standard Orthophosphate-phosphorus 6.9 Begin analysis. When the peak from the solution II concentration (mL) (mg/L) most concentrated standard appears on the recorder, adjust the STD CAL control until the 0.0 0.00 1.0 .05 flat portion of the peak reads full scale. 2.0 .10 5.0 .25 7. Calculations 10 .50 20 1.00 7.1 Prepare an analytical curve by plotting the height of each standard peak versus its 5.9 Sulfuric acid, 2.45M: Cautiously, add respective orthophosphate-phosphorus concen­ slowly, with constant stirring and cooling, 136 tration. mL concentrated sulfuric acid (sp gr 1.84) to 800 7.2 Compute the concentration of dissolved mL demineralized water and dilute to 1 L with or total phosphorus in each sample by compar­ demineralized water. ing its peak height to the analytical curve. Any 5.10 Sulfuric acid, 0.45M; Cautiously, add baseline drift that may occur must be taken into slowly, with constant stirring and cooling, 25.2 account when computing the height of a sam­ mL concentrated sulfuric acid (sp gr 1.84) to 800 ple or standard peak. mL demineralized water and dilute to 1 L with demineralized water. 8. Report 5.11 Water diluent: Dissolve 20 g NaCl in 800 Report phosphorus, orthophosphate plus mL demineralized water. Add 2.0 mL Levor V hydrolyzable, dissolved (00677), and total and dilute to 1 L with demineralized water. (00678), concentrations as follows: less than 1 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 379

no. 0.030ln Air >73H!>3 5-turn coite O.32mL/mlh

tbtbiU^Qi 0.030in Water diluent / MM^ . ffflB«.j• j 0.32mL/mln H«ating bath 3> _ 37.5°C 0.035ln r Sampler 4 0.42mL/mln 40/h 5/1 cam Co lorlmeter 0.03Oln Combined reagent 88 Onm* Watte 0.32mL/mln 15 -mm cell^ r To satnpl er 4 Wash solution th -* 0.073ln i iva« 2.00mL/mln t rec•pttacle i^HHH 0.040ln Waste ^ 0.60mL/mln R«cord«r Pnportioning pump

Alternativelyi 660 nm Figure 38.—Phosphorus, phosphomolybdate manifold mg/L, two decimals; 1 mg/L and above, two References significant figures. Gales, M. E,t Jr., Julian, E. C.t and Kroner, R. C., 1966, 9. Precision Method for quantitative determination of total phos­ It is estimated that the percent relative stand­ phorus in water: American Water Works Association ard deviation for dissolved and total ortho- Journal, v. 58, p. 1363-8. phosphate plus hydrolyzable phosphorus will be Murphy J., and Hiley, J. P., 1962, A modified single-solution equal to that reported for phosphorus by the method for the determination of phosphate in natural automated phosphomolybdate method. waters: Analytica Chimica Acta, v. 27, p. 31-6.

Phosphorus, orthophosphate, colorimetrjc, phosphomolybdate

Parameter and Code: Phosphorus, orthophosphate, dissolved, 1-1601-85 (mg/L as P): 00671

1. Application reagents. Nitrite interferes but can be oxidized This method may be used to analyze most to nitrate with hydrogen peroxide before water and wastewater containing between 0.02 analysis. Residual chlorine must be removed by and 0.4 mg/L of orthophosphate-phosphorus. boiling the sample. Samples containing greater concentrations need 3.2 Mercuric chloride interferes when the to be diluted. chloride concentration is less than 50 mg/L. Mercuric chloride-preserved samples are for- 2. Summary of method tified with a minimum of 85 mg/L NaCl to over­ 2.1 As far as is known, the phosphomolyb­ come this interference. date method is specific for the orthophosphate 3.3 Arsenic as arsenate (AsO43) produces a form of phosphorus. Weak tests are reported color similar to that of phosphate (Murphy and with pyrophosphate and polyphosphates, but Riley, 1962) and may cause a positive inter­ these positive tests may well result from or­ ference. Arsenic concentrations as much as 100 thophosphate contamination of the material. /ig/L do not interfere. Greater concentrations 2.2 Orthophosphate is converted to phos­ were not investigated. phomolybdate by acidified ammonium molyb- date reagent: 4. Apparatus Spectrometer for use at 700 or 882 nm. H3PO4 + 12

Number of Relative standard deviation 7. Calculations laboratories (mg/L) _____(percent)_____ 7.1 Determine the milligrams of phosphorus 11 0.000 0 in. each sample from a plot of absorbances of 12 .008 62 15 .406 11 standards. 11 1.02 8 7.2 Determine the phosphorus concentra­ 14 1.70 13 tion in milligrams per liter as follows: Reference

1,000 Murphy, J.f and Riley, J. P., 1962, A modified single-solution P (mg/L) = X mg P in sample method for the determination of phosphate in natural mT. sample waters: Analytica Chimica Acta, v. 27, p. 31-6. Phosphorus, orthophosphate, colorimetrijc, phosphomolybdate, automated-segmented flow

Parameters and Codes: Phosphorus, orthophosphate, dissolved, 1-2601-85 (mg/L as P): 00671 Phosphorus, orthophosphate, total, 1-4601-85 (mg/L as P): 70507

1. Application interference from silica, which forms a pale-blue 1.1 This method may be used to analyze most complex, is slight and can be considered negligi­ water, wastewater, brines, and water-suspended ble. Nitrite interferes, but can be oxidized to sediment containing between 0.01 and 1.0 mg/L nitrate with hydrogen peroxide before analysis. orthophosphate-phosphorus. Residual chlorine must be removed by boiling 1.2 Total orthophosphate-phosphorus is the sample. determined by allowing the suspended sediment 3.3 Mercuric chloride interferes when the in an unfiltered, unacidified sample to settle in chloride concentration is less than 50 mg/L. the sample bottle and by decanting a portion 3.4 Arsenic as arsenate (AsO^3) produces a of the clear supernatant solution for analysis. color similar to that of phosphate (Murphy and Riley, 1962) and may cause a positive inter­ 2. Summary of method ference. Arsenic concentrations as much as 100 2.1 Orthophosphate ion reacts with am­ /ig/L do not interfere. Greater concentrations monium molybdate in acidic solution to form were not investigated. phosphomolybdic acid, which upon reduction with ascorbic acid produces an intensely colored 4. Apparatus blue complex. Antimony potassium tartrate is 4.1 Technicon AutoAnalyzer //, consisting added to increase the rate of reduction (Murphy of sampler, cartridge manifold, proportioning and Riley, 1962; Gales and others, 1966). pump, heating bath, colorimeter, voltage sta­ 2.2 Mercuric chloride-preserved samples are bilizer, recorder, and printer. fortified with a minimum of 85 mg/L NaCl to 4.2 With this equipment the following overcome the interference from mercury in the operating conditions have been found satisfac­ analysis. tory for the range from 0.01 to 1.0 mg/L P: Absorption cell ——— 50 mm 3. Interferences Wavelength ————— 880 nm or 3.1 Because as phosphorus is easily ad­ 660 nm sorbed on sediment, the orthophosphate recov­ Cam —————————— 40/h (5/1) ered from the supernatant solution above a Heating bath ———— 37.5 °C water-suspended sediment after some time has elapsed may be less than the orthophosphate 5. Reagents that would have been determined in the filtrate 5.1 Ammonium molybdate solution, 35.6 from a sample filtered at the time of collection. g/L: Dissolve 40 g ammonium molybdate, The amount recovered may also depend on the (NH4)6Mo7O24'4H2O, in 800 mL demineralized type of sediment (clay, sand, etc.). water and dilute to 1 L. 3.2 Barium, lead, and silver interfere by 5.2 Ascorbic acid solution, 18 g/L: Dissolve forming a phosphate precipitate, but the effect 18 g ascorbic acid (C6H8O6) in 800 mL demin­ is usually negligible in natural waters. The eralized water and dilute to 1 L.

383 384 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

5.3 Antimony potassium tartrate solution, Phosphate standard Orthophosphate-phosphorus solution II concentration 3 g/L: Dissolve 3.0 g antimony potassium tar­ (mL) (mg/L) trate, K(SbO)C4H4O6-1/2H2O, in 800 mL demin- 0.0 0.00 eralized water and dilute to 1 L. 1.0 .05 5.4 Combined working reagent: Combine 2.0 .10 reagents together in order and volumes listed 5.0 .25 10 .50 below. This reagent is stable for about 8 hr: 20 1.00 Sulfuric acid, 2.45M ———— 50 mL Ammonium molybdate solu­ 5.9 Sulfuric acid, 2.45M: Cautiously, add tion ———————————— 15 mL slowly, with constant stirring and cooling, 136 Ascorbic acid solution —— 30 mL mL concentrated sulfuric acid (sp gr 1.84) to 800 Antimony potassium tartrate mL demineralized water. Cool and dilute to 1 solution ————————— 5 mL L with demineralized water. 5.5 Levor V solution or equivalent. 5.10 Water diluent: Dissolve 20 g NaCl in 800 5.6 Phosphate standard solution I, 1.00 mL demineralized water. Add 2.0 mL Levor V mL = 0.100 mg P: Dissolve 0.4394 g KH2PO4, and dilute to 1 L with demineralized water. dried overnight over concentrated H2SO4 (sp gr 1.84), in demineralized water and dilute to 1,000 6. Procedure mL. 6.1 Set up manifold (fig. 39). 5.7 Phosphate standard solution II, 1.00 6.2 Allow colorimeter, recorder, and heating mL = 0.010 mg P: Dilute 100.0 mL phosphate bath to warm for at least 30 min or until the standard solution I to 1,000 mL with deminer­ temperature of the heating bath is 37.5 °C. alized water. 6.3 Adjust the baseline to read zero scale 5.8 Phosphate working standards: Prepare divisions on the recorder for all reagents, but a blank and 200 mL each of a series of working with demineralized water in the sample line. standards by appropriate quantitative dilution 6.4 Place a complete set of standards and a of phosphate standard solution II. Dissolve 10 blank in the first positions of the first sample mg mercuric chloride and 120 mg sodium tray, beginning with the most concentrated chloride in each working standard. For example:

no. 0.030ln Air S73-03 5-turn coils O.32mL/mln

(BflHUI£| flnHH01 V O.OSOin Water diluent /

J L 0.32mL/mln 1J Heating bath ^ I 37.5°C 0.035!n 3 r Sampler 4 O.42mL/mln 4O/h 5/1 cam Colorimeter 0.030ln Combined reagent 880nm* Waete 0.32mL/mln 1 5-mm cell^i r To sampler 4 0.073ln Wash solution 2.00mL/mln T receptacle 0.040ln Waste T~ 0.60mL/mln I Recorder Proportioning pump

* Alternatively 660 nm Figure 39.—Phosphorus, phosphomolybdate manifold METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 385 concentrations in approximately every eighth range of 0.007 to 1.93 mg/L may be expressed position of the remainder of this and subsequent as follows: sample trays. Fill remainder of each tray with unknown samples (NOTE 1). 0.015 NOTE 1. For water-suspended sediment, decant a portion of the clear supernatant solution from where a settled sample for analysis. Avoid transfer of ST = overall precision, milligrams per liter, any participate matter to the sample cups. and 6.5 Begin analysis. When the peak from the X s= concentration of orthophosphate-phos­ most concentrated standard appears on the phorus, milligrams per liter. recorder, adjust the STD CAL control until the The correlation coefficient is 0.8580. flat portion of the curve reads full scale. 9.2 Precision for dissolved orthophos­ phate-phosphorus for four of the nine samples 7. Calculations expressed in terms of percent relative standard 7.1 Prepare an analytical curve by plotting deviation is as follows: the height of each standard peak versus its Number of Mean Relative standard deviation respective orthophosphate-phosphorus concen­ laboratories (mp/L) ____(percent)____ tration. 3 0.007 86 7.2 Compute the concentration of dissolved 20 .404 11 or total orthophosphate-phosphorus in each 18 1.07 10 sample by comparing its peak height to the 17 1.93 13 analytical curve. Any baseline drift that may 9.3 It is estimated that the percent relative occur must be taken into account when com­ standard deviation for total orthophos­ puting the height of a sample or standard phate-phosphorus will be equal to or greater peak. than that reported for dissolved orthophos­ phate-phosphorus. 8. Report Report phosphorus, orthophosphate, dis­ References solved (00671), and total (70507), concentrations as follows: less than 1 mg/L, two decimals; 1 Gales. M. E., Jr.t Julian, E. C.f and Kroner, R. C., 1966, mg/L and above, two significant figures. Method for quantitative determination of total phos­ phorus in water: American Water Works Association Journal, v. 58, p. 1363-8. 9. Precision Murphy, J.t and Rttey, J. P., 1962, A modified single-solution 9*1 Precision for dissolved orthophos­ method for the determination of phosphate in natural phate-phosphorus for 9 samples within the waters: Analytics Chimica Acta, v. 27, p. 31-6.

Phosphorus, orthophosphate, colorimetric, phosphomolybdate, automated-discrete

Parameters and Codes: Phosphorus, orthophosphate, dissolved, 1-2598-85 (mg/L as P): 00671 Phosphorus, orthophosphate, total, I-4598-85 (mg/L as P): 70507

1. Application 3.2 Barium, lead, and silver interfere by 1.1 This method may be used to analyze forming a precipitate. The interference from water, wastewater, brines, and water-suspended silica, which forms a pale-blue complex, is slight sediment containing from 0.01 to 2.0 mg/L and can be considered negligible. Nitrite in­ orthophosphate-phosphorus. Samples contain­ terferes, but can be oxidized to nitrate with ing concentrations greater than 2.0 mg/L need hydrogen peroxide before analysis. Residual to be diluted. chlorine must be removed by boiling the sample. 1.2 To determine total orthophosphate- 3.3 Arsenic as arsenate (AsO^3) produces a phosphorus, the suspended sediment in an un- color similar to that of phosphate (Murphy and filtered, unacidified sample is allowed to settle Riley, 1962) and may cause a positive inter­ in the sample bottle and a portion of the clear ference. Arsenic concentrations up to 100 pglL supernatant solution is decanted for analysis. do not interfere. Greater concentrations were not investigated. 2. Summary of method 3.4 The blue color produced will coat the 2.1 Orthophosphate ion reacts with am­ flow cell, causing a small but significant high monium molybdate in acidic solution to form bias. A 0.10-mg/L P spike is dispensed into the phosphomolybdic acid, which, upon reduction four leading wash tubes with the color reagent. with ascorbic acid, produces an intensely col­ The resulting blue color then coats the flow cell ored blue complex. Antimony potassium tar- prior to the introduction of the working stand­ trate is added to increase the rate of reduction ards. By this action, the high bias is effectively (Murphy and Riley, 1962; Gales and others, eliminated. 1966). 2.2 Mercuric chloride-preserved samples are 4. Apparatus fortified with a minimum of 85 mg/L NaCl to 4.1 Discrete chemical analyzer system, overcome the interference from mercury in the American Monitor IQAS or equivalent. analysis. 4.2 With this equipment, the following oper­ ating conditions have been found satisfactory: 3. Interferences Wavelength -- 880 nm 3.1 Because as phosphorus is easily ad­ Absorption cell 1-cm square, temper­ sorbed on sediment, the orthophosphate ature-controlled, flow- recovered from the supernatant solution above through quartz a water-suspended sediment after some time cuvette has elapsed may be less than the ortho- Reaction phosphate that would have been determined in temperature 37 °C the filtrate from a sample filtered at the time Sample volume 0.300 mL with 0.050 of collection. The amount recovered may also mL of diluent depend on the type of sediment (clay, sand, etc.). (NOTE 1)

387 388 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Reagent volumes 0.25 mL color reagent 5.8 Phosphate standard solution III (spike), and 0.80 mL deminer- 1.00 mL = 0.0001 mg P: Dilute 2.0 mL of alized water (NOTE 1) phosphate standard solution II to 1,000 mL NOTE 1. Sample-to-diluent ratio and reagent with demineralized water. volumes must be optimized for each instrument according to manufacturer's specifications. 6. Procedure 6.1 Set up analyzer and computer-card 5. Reagents assignments according to manufacturer's in­ 5.1 Ammonium molybdate solution, 35.6 structions. g/L: Dissolve 40 g ammonium molybdate, 6.2 Place standards, beginning with the (NH4)6Mo7O24'4H2O, in 800 mL demineralized water and dilute to 1 L. lowest concentrations, in ascending order 5.2 Antimony potassium tartrate solution, (computer-calibration curve) in the first five 3 g/L: Dissolve 3.0 g antimony potassium tar­ positions on the sample turntable. Place trate, K(SbO)C4H4O6-1/2H2O, in 800 mL demin­ samples and quality-control standards in the re­ eralized water and dilute to 1 L. mainder of the sample turntable. 5.3 Ascorbic acid solution, 18 g/L: Dissolve 6.3 Begin analysis. The cathode-ray tube 18 g ascorbic acid (C6H8O6) in 800 mL demin­ (CRT) will acknowledge the parameter and con­ eralized water and dilute to 1 L. centration range, listing each sample-cup 5.4 Combined working reagent: Combine number and the corresponding concentration reagents in order and volumes listed below. This calculated from the working curve. During each reagent is stable for about 8 h. run, the CRT display will provide a plot of Sulfuric acid, 2.45M ———— 50 mL standards, samples, and list blank and slope Ammonium molybdate solu­ calculations. Retain copy of all information ob­ tion ———————————— 15 mL tained from printer. Ascorbic acid solution - 30 mL Antimony potassium tartrate 7. | Calculations solution ——————————— 5 mL Determine the concentration in milligrams 5.5 Phosphate standard solution J, 1.00 per liter of dissolved or total orthophosphate- mL = 1.00 mg P: Dissolve 4.394 g KH2PO4, phosphorus in each sample from either the CRT dried overnight over concentrated H2SO4 (sp gr display or the printer output. 1.84), in demineralized water and dilute to 1,000 mL. 8. Report 5.6 Phosphate standard solution II, 1.00 mL = 0.05 mg P: Dilute 50.0 mL phosphate Report phosphorus, orthophosphate, dis­ standard solution I to 1,000 mL with deminer­ solved (00671), and total (70507), concentrations alized water. as follows: less than 1.0 mg/L, two decimals; 1.0 5.7 Phosphate working standards: Prepare mg/L and above, two significant figures. a blank and 1,000 mL each of a series of phosphate working standards by appropriate 9. Precision quantitative dilution of phosphate standard The precision expressed in terms of the stand­ solution II with demineralized water. Dissolve ard deviation and percent relative standard 52 mg mercuric chloride and 600 mg sodium deviation for replicate analysis of reference chloride in each working standard. For example: materials by a single operator is as follows:

Standard solution 11 Orthophosphate-phosphorus concentration Relative standard (ml) (mo/L) Mean Number of Standard deviation deviation

Parameters and Codes: Phosphorus, orthophosphate, dissolved, 1-2057-85 (mg/L as P): 00671 Phosphorus, orthophosphate, dissolved, I-2058-85 (mg/L as P): 00671

2. Summary of method separated anions in their acid form are measured Orthophosphate is determined sequentially using an electrical-conductivity cell See method with six other anions by ion-exchange chro- 1-2057, anions, ion-exchange chromatographic, matography. Ions are separated based on their automated, and 1-2058, anions, ion-exchange affinity for the exchange sites of the resin. The chromatographic, precipitation, automated. 389

Phosphorus, hydrolyzable and organic, calculation

Parameters and Codes: ! Phosphorus, hydrolyzable, dissolved (mg/L as P): 00672 Phosphorus, hydrolyzable, total (mg/L as P): 00669 Phosphorus, organic, dissolved (mg/L as P): 00673 Phosphorus, organic, total (mg/L as P): 00670

1. Application hydrolyzable phosphorus from dissolved or This method may be used to calculate dis­ total phosphorus, respectively. solved and total hydrolyzable phosphorus, and dissolved and total organic phosphorus, on 7. Calculations which the following parameters have been 7.1 Phosphorus, hydrolyzable, dissolved determined: (mg/L) = phosphorus, orthophosphate plus hydrolyzable, dissolved (mg/L)—phosphorus, or­ Parameters Method No. thophosphate, dissolved (mg/L). 7.2 Phosphorus, hydrolyzable, total Phosphorus, orthophosphate, (mg/L) = phosphorus, orthophosphate plus dissolved M601 or hydrolyzable, total (mg/L)—phosphorus, ortho- 1-2601 or phosphate, total (mg/L). 1-2598 7.3 Phosphorus, organic, dissolved (mg/L) = Phosphorus, orthophosphate, phosphorus, dissolved (mg/L)—phosphorus, or­ total 1-4601 or thophosphate plus hydrolyzable, dissolved 1-4598 (mg/L). Phosphorus, orthophosphate 7.4 Phosphorus, organic, total (mg/L) = plus hydrolyzable, dissolved 1-1602 or phosphorus, total (mg/L)—phosphorus, ortho- 1-2602 phosphate plus hydrolyzable, total (mg/L). Phosphorus, orthophosphate plus hydrolyzable, total 1-4602 8. Report Phosphorus, dissolved M600 or Report phosphorus, hydrolyzable, dissolved 1-2600 or (00672); phosphorus, hydrolyzable, total 1-2599 (00669); phosphorus, organic, dissolved (00673); Phosphorus, total 1-4600 or and phosphorus, organic, total (00670), as 1-4599 follows: less than 1 mg/L, two decimals; 1 mg/L and above two significant figures. 2. Summary of method Dissolved or total hydrolyzable phosphorus 9* Precision is determined by subtracting dissolved or total See the individual methods: phosphorus, or­ orthophosphate-phosphorus from dissolved or thophosphate, dissolved or total; phosphorus, total orthophosphate plus hydrolyzable phos­ orthophosphate plus hydrolyzable, dissolved or phorus, respectively. Dissolved or total organic total; and phosphorus, dissolved or total. Preci­ phosphorus is determined by subtracting sion will depend on the precision obtained for dissolved or total orthophosphate plus each method.

391

Potassium, atomic absorption spectrometric, direct

Parameters and Codes: Potassium, dissolved, 1-1630-85 (mg/L as K): 00935 Potassium, total recoverable, I-3630-85 (mg/L as K): none assigned Potassium, recoverable-from-bottom-material, dry wt, I-5630-85 (mg/kg as K): 00938

1. Application Potassium found 1.1 This method may be used to analyze at­ (mp/L) mospheric precipitation, water, brines, and 1.00 1.00 water-suspended sediment. 1.00 1.03 1.2 Two analytical ranges for potassium are 1.00 1.05 included: from 0.01 to 1.0 mg/L and from 0.10 1.00 1.07 to 10.0 mg/L. Sample solutions containing 3.2 Alternatively, an excess of sodium or potassium concentrations greater than 10 mg/L cesium may be added to all samples and stand­ need to be diluted. ards. Such additions essentially eliminate the 1.3 This method may be used to analyze bot­ effects of the then comparatively minor con­ tom material containing at least 10 mg/kg of tributions of sodium present in the samples. potassium. 1.4 Total recoverable potassium in water- 4. Apparatus suspended sediment needs to undergo prelimi­ 4.1 Atomic absorption spectrometer nary digestion-solubilization by method 1-3485 equipped with electronic digital readout and and recoverable potassium in bottom material automatic zero and concentration controls. needs to undergo preliminary digestion-solubiliza­ 4.2 Refer to the manufacturer's manual to tion by method 1-5485 before being determined. optimize instrument for the following: Grating ——————— Visible 2. Summary of method Wavelength ————— 766.5 nm 2.1 Potassium is determined by atomic ab­ Source (hollow-cathode sorption spectrometry by direct aspiration of lamp) ———————— Potassium the sample solution into an air-acetylene flame Oxidant ———————— Air (Fishman and Downs, 1966). Fuel ————————— Acetylene 2.2 The procedure may be automated by the Type of flame ———— Slightly reducing addition of a sampler and either a strip-chart 4.3 The 50-mm (2-in.), flathead, single-slot recorder or a printer. burner allows working ranges of 0.01 to 1.0 mg/L and 0.1 to 10 mg/L. The burner, rotated 3. Interferences 90°, extends the range to 100 mg/L. Different 3.1 Of the substances commonly occurring burners may be used according to manufac­ in water, only sodium has been found to inter­ turers' instructions. fere, and its interference is greatly minimized if a reducing flame is used and the burner is 5. Reagents raised to approximately 0.05 cm below the op­ 5.1 Potassium standard solution 7, 1.00 tical light path. The following data are in­ mL = 0.100 mg K: Dissolve 0.1907 g KC1, dried dicative of the magnitude of sodium at 180°C for 1 h, in demineralized water and interference under these conditions: dilute to 1,000 mL. 393 394 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Potassium working standards: Prepare 9. Precision a series of at least six working standards con­ 9.1 Precision for dissolved potassium for 36 taining either from 0.01 to 1.0 mg/L or from 0.1 samples within the range of 0.09 to 26.1 mg/L to 10.0 mg/L of potassium by appropriate dilu­ may be expressed as follows: tion of potassium standard solution I. - 0.050 6. Procedure While aspirating the blank use the automatic where zero control to set the digital display to read ST = overall precision, milligrams per liter, zero concentration. While aspirating standards and use the automatic concentration control to set X = concentration of potassium, milligrams the digital display to read the concentration of per liter. standards. Use at least six standards. Calibrate The correlation coefficient is 0.9350. the instrument each time a set of samples is 9.2 Precision for dissolved potassium for analyzed and check calibration at reasonable in­ five of the 36 samples expressed in terms of the tervals. percent relative standard deviation is as follows:

Number of Mean Relative standard deviation 7. Calculations laboratories (mg/L) _____(percent)_____ 7.1 Determine the milligrams per liter of 24 0.09 55 dissolved or total recoverable potassium in each 17 2.48 10 sample from the digital display or printer while 32 5.20 11 23 11.7 8 aspirating each sample. Dilute those samples 19 26.1 13 containing potassium concentrations that ex­ ceed the working range of the method and 9.3 Precision for dissolved potassium within multiply by the proper dilution factors. the range of 0.01 to 1.0 mg/L in terms of the per­ 7.2 To determine milligrams per kilogram of cent relative standard deviation by a single potassium in bottom-material samples, first operator is as follows: determine the milligrams per liter of potassium Number of Relative standard deviation as in paragraph 7.1; then: replicates _____(percent)_____

18 38.9 mL original digest 12 9.7 mg/L K X 11 2.7 K (mg/kg) = 1000 10 1.8 wt of sample (kg) 11 4.6 9.4 It is estimated that percent relative 8. Report standard deviation for total recoverable potas­ 8.1 Report potassium, dissolved (00935), and sium and for recoverable potassium from bot­ total recoverable (none assigned), concentra­ tom material will be greater than that reported tions as follows: less than 1.0 mg/L, two for dissolved potassium. decimals; 1.0 to 10 mg/L, one decimal; 10 mg/L and above, two significant figures. 8.2 Report potassium, recoverable-from- Reference bottom-material (00938), concentrations as follows: less than 1,000 mg/kg, nearest 10 Fishman, M. J., and Downs, S. C., 1966, Method for analysis mg/kg; 1,000 mg/kg and above, two significant of selected metals in water by atomic absorption: U.S. figures. Geological Survey Water-Supply Paper 1540-C, p. 36-8. Potassium, atomic absorption spectrometric, direct-EPA

Parameter and Code: ; Potassium, total recoverable, 1-3631-85 (mg/L as K): 00937

1. Application 3.2 Alternatively, an excess of sodium or 1.1 This method may be used to analyze cesium may be added to all samples and stand­ water-suspended sediment Sample solutions ards. Such additions essentially eliminate the ef­ containing from 0.1 to 100 mg/L of potassium fects of the then comparatively minor may be analyzed without dilution, but those con­ contributions of sodium present in the samples. taining more than 100 mg/L need to be diluted. 1.2 For ambient water, analysis may be made 4. Apparatus on a portion of the acidified water-suspended 4.1 Atomic absorption spectrometer sediment sample equipped with electronic digital readout and 1.3 For all other water, including domestic automatic zero and concentration controls. and industrial effluent, the atomic absorption 4.2 Refer to the manufacturer's manual to procedure must be preceded by a digestion* optimize instrument for the following: solubilization as specified below. In cases where Grating ————————— Visible the analyst is uncertain about the type of Wavelength —————— 766.5 nm sample, the digestion-solubilization procedure Source (hollow-cathode must be used. lamp) ———————— Potassium Oxidant ———————— Air 2. Summary of method Fuel —————————— Acetylene 2.1 Potassium is determined by atomic ab­ sorption spectrometry by direct aspiration of the Type of flame ———— Slightly reducing filtered or digested and filtered sample into an 4.3 The 50-mm (2-in.), flathead, single-slot air-acetylene flame (Fishman and Downs, 1966). burner allows a working range of 0.1 to 10 mg/L. 2.2 Effluent samples must undergo a The burner, rotated 90°, extends the range to 100 preliminary nitric acid digestion followed by a mg/L. Different burners may be used according hydrochloric acid solubilization. to manufacturers' instructions.

3. Interferences 5. Reagents 3.1 Of the substances commonly occurring in 5.1 Hydrochloric acid, 6Af: Dilute 500 mL water, only sodium has been found to interfere, concentrated HC1 (sp gr 1.19) to 1 L with demin- and its interference is greatly minimized if a reduc­ eralized water. ing flame is used and the burner is raised to ap­ 5.2 Hydrochloric acid, 0.3M: Dilute 25 mL proximately 0.05 cm below the optical light path. concentrated HC1 (sp gr 1.19) to 1 L with demin- The following data are indicative of the magnitude eralized water. of sodium interference under these conditions: 5.3 Nitric acid, concentrated, (sp gr 1.41). 5.4 Potassium standard solution /, 1.00 mL = Potassium found 0.100 mg K: Dissolve 0.1907 g KC1, dried at (mgJL) 180 °C for 1 h, in demineralized water and dilute 1.00 1.00 to 1,000 mL. 1.00 1.03 too 1.05 5.5 Potassium working standards: Prepare 1.00 1.07 a series of at least six working standards 395 396 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS containing from 0.1 to 100 mg/L of potassium control to set the digital display to read the con­ by appropriate dilution of potassium standard centration of standards. Use at least six stand­ solution. ards. Calibrate the instrument each time a set of samples is analyzed and check calibration at 6. Procedure reasonable intervals. 6.1 Transfer the entire sample to a beaker. 6.2 Rinse the sample bottle with 3 mL con­ 7. Calculations centrated HNO3 for each 100 mL of sample and Determine the milligrams per liter of total add to the beaker. Prepare a blank using 3 mL recoverable potassium in each sample from the concentrated HNO3 per 100 mL demineralized digital display or printer while aspirating each water. sample. Dilute those samples containing 6.3 Evaporate samples and blank to dryness potassium concentrations that exceed the work­ on a hotplate, making sure the samples do not ing range of the method and multiply by the boil. proper dilution factors. 6.4 Cool and add an additional 3 mL concen­ trated HNO3 to each beaker. Cover with a 8. Report watchglass, return to the hotplate, and gently Report potassium, total-recoverable (00937), reflux the samples. concentrations as follows: less than 10 mg/L, 6.5 Continue heating, adding additional acid one decimal; 10 mg/L and above, two significant as necessary, until the digestion is complete (in­ figures. dicated by a light-colored residue). Evaporate just to dryness. 9. Precision 6.6 Add 6 mL 6M HC1 solution per 100 mL It is estimated that the percent relative stand­ original sample and warm the beaker to dissolve ard deviation for total recoverable potassium the residue. over the range of the method will be greater 6.7 Wash the watchglass and beaker with than 13 percent. demineralized water and filter the sample (Whatman No. 41 or equivalent), rinsing the References filter with hot 0.3M HC1. Dilute to the original volume with demineralized water. Fishman, M. J., and Downs, S. C., 1966, Method for analysis 6.8 While aspirating the blank use the of selected metals in water by atomic absorption: U.S. Geological Survey Water-Supply Paper 1540-C, p. 36-8. automatic zero control to set the digital display U.S. Environmental Protection Agency, 1979, Methods for to read zero concentration. While aspirating chemical analysis of water and wastes: Cincinnati, standards use the automatic concentration p. 258.1-1. Potassium, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Potassium, total, 1-5473-85 (mg/kg as K): none assigned Potassium, total, 1-5474-85 (mg/kg as K): none assigned

2. Summary of method method 1-5473, metals, major, total-in-sediment, 2.1 A sediment sample is dried, ground, and atomic absorption spectrometric, direct. homogenized. The sample is then treated and 2.1.2 The sample is digested with a combina­ analyzed by one of the following techniques. tion of nitric, hydrofluoric, and perchloric acids 2.1.1 The sample is fused with a mixture of in a Teflon beaker heated on a hot plate at lithium metaborate and lithium tetraborate in a 200 °C. Potassium is determined on the result­ graphite crucible in a muffle furnace at 1000 °C. ing solution by atomic absorption spectrometry. The resulting bead is dissolved in acidified, boil­ See method 1-5474, metals, major and minor, ing, demineralized water, and potassium is deter­ total-in-sediment, atomic absorption spec­ mined by atomic absorption spectrometry. See trometric, direct. 397

Selenium, atomic absorption spectrometric, hydride

Parameters and Codes: Selenium, dissolved, 1-1667-85 fcg/L as Se): 01145 Selenium, total, I-3667-85 (^g/L as Se): 01147 Selenium, suspended total, (-7667-85 (jig/L as Se): 01146 Selenium, total-in-bottom-material, dry wt, 1-5667-85 0*9/9 as Se): 01148

1. Application flame where it is determined by atomic absorp­ 1.1 This method may be used to analyze tion at 196.0 nm (Freeman and Uthe, 1974; water and water-suspended sediment containing Lansford and others, 1974). at least 1 /ig/L of selenium. Samples containing more than 20 ptg/L need to be diluted. 3. Interferences 1.2 Suspended total selenium is calculated by 3.1 Arsenic interferes by suppressing the subtracting dissolved selenium from total selenium absorption if an excess of stannous selenium. chloride is used. This interference can be 1.3 This method may be used to analyze bot­ avoided by carefully controlling the amount of tom material containing at least 1 /ig/g of selen­ stannous chloride added. If 42 mg stannous ium. Usually a 100-mg sample of prepared bottom chloride is added, as much as 150 jig/L of arsenic material (method P-0520) is taken for analysis. can be tolerated. At least this amount must be However, if the sample contains more than 20 ptg/g added, however, to ensure efficient reduction of of selenium, a smaller sample needs to be used. selenite to the hydride. 1.4 Total selenium in water-suspended sedi­ 3.2 Mercury interferes when its concentra­ ment may be determined after each sample has tion exceeds 25 /ig/L. been thoroughly mixed by vigorous shaking and i a suitable sample portion has been rapidly 4. Apparatus withdrawn from the mixture. 4.1 Atomic absorption spectrometer. 4.2 Refer to the manufacturer's manual to 2. Summary of method optimize instrument for the following: Organic selenium compounds, if present, are Grating ———————— Ultraviolet first decomposed by digestion with potassium Wavelength ————— 196.0 nm permanganate in hot acidic solution. The solu­ Source (electrodeless tion is then made basic and evaporated to discharge lamp) — Selenium dryness in the presence of calcium chloride to Burner ———————— Three-slot prevent loss of selenate during the evaporation. Fuel —————————— Hydrogen Hydrochloric acid is added to the residue to Diluent ———————— Nitrogen reduce the selenate to selenite. Quantitative Carrier ———————— Nitrogen reduction without loss of selenium requires con­ 4.3 Selenium hydride vapor analyzer (fig. 40) trol of the temperature, time, and acid concen­ consisting of — tration. All selenium must be in the selenite 4.3.1 Fleaker, 300-mL capacity, or beaker, form prior to its final reduction with stannous Berzelius, 200-mL capacity. chloride in 6M hydrochloric acid solution. The 4.3.2 Gas dispersion tube, coarse frit (Scien­ selenium hydride so formed is subsequently tific Glass Apparatus Co. No. JG-8500 has been removed from solution by aeration and swept found satisfactory). by a flow of nitrogen into a hydrogen diffusion 4.3.3 Medicine dropper, 2-mL capacity min. 399 400 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Auxiliary nitrogen Burner

Gas dispersion tube Dropper

Outlet tube

Rubber stopper

Hydrogen Nitrogen

200-mL Berzelius beaker or 300-ml fleaker Figure 40.—Selenium hydride vapor analyzer

5. Reagents g/L: Dissolve 0.3 g KMnO4 in 1 L demineralized 5.1 Ammonium chloride solution, 250 g/L: water. Dissolve 250 g NH4C1 in demineralized water 5.8 Selenium standard solution I, 1.00 and dilute to 1 L. mL = 1.00 mg Se: Dissolve 2.3928 g Na2SeO4 5.2 Calcium chloride solution, 22.6 g/L: in demineralized water. Add 1 mL concentrated Dissolve 30 g CaCl2-2H2O in demineralized HNO3 (sp gr 1.41) and dilute to 1000 mL with water and dilute to 1 L. demineralized water. 5.3 Hydrochloric acid, concentrated (sp gr 5.9 Selenium standard solution II, 1.00 1.19). mL = 10.0 jig Se: Dilute 10.0 mL selenium 5.4 Hydrochloric acid, 6Af: Dilute 500 mL standard solution I and 1 mL concentrated concentrated HC1 (sp gr 1.19) to 1L with demin­ HNO3 (sp gr 1.41) to 1000 mL with demineral­ eralized water. ized water. Discard after 3 months. 5.5 Hydrochloric acid, 0.1M: Dilute 8 mL con­ 5.10 Selenium standard solution III, 1.00 centrated HC1 (sp gr 1.19) to 1 L with deminer­ mL = 0.100 ng Se: Dilute 5.00 mL selenium alized water. standard solution II and 1 mL concentrated 5.6 Methyl orange indicator solution, 50 HNO3 (sp gr 1.41) to 500 mL with demineral­ mg/100 mL: Dissolve 50 mg methyl orange in 100 ized water. Prepare fresh weekly. mL demineralized water. 5.11 Sodium hydroxide solution, 0.1M: Dissolve 5.7 Potassium permanganate solution, 0.3 4 g NaOH in demineralized water and dilute to 1 L. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 401 5.12 Stannous chloride solution, 4.2 g/100 mL to dryness, and allow the fleakers to cool. concentrated HC1: Dissolve 5 g SnCl2'2H2O in Avoid prolonged heating of the residue. 100 mL concentrated HC1 (sp gr 1.19). This solu­ 6.8 Add 5 mL concentrated HC1 and 10 mL tion is unstable. Prepare fresh daily. NH4C1 solution. Heat in a boiling-water or steam bath for 20 + 0.5 min (NOTE 3). 6. Procedure NOTE 3. Samples can be heated on a hotplate 6.1 Follow instructions in paragraph 6.1.1 at low temperature if boiling can be prevented. for waters and water-suspended sediment mix­ 6.9 Dilute each sample, blank, and standard tures and in paragraph 6.1.2 for bottom to approx 100 mL with 6M HC1. materials. 6.10 Attach one fleaker at a time to the rub­ 6.1.1 Pipet a volume of well-mixed sample con­ ber stopper containing the gas dispersion tube. taining less than 2.0 jig Se (100 mL max) into 6.11 Fill)the medicine dropper with 1 mL a 300-mL fleaker and dilute to 100 mL. SnCl2 solution and insert into hole in rubber 6.1.2 Weigh a portion of prepared bottom- stopper. material sample containing less than 2.0 fig Se 6.12 Add the SnCl2 solution to the sample (100 mg max); transfer to a 300-mL fleaker and solution. After the absorbance has reached a add 100 mL demineralized water (NOTE 1). Stir maximum and has returned to the baseline, to mix thoroughly and allow to settle. remove the fleaker. Rinse the gas dispersion NOTE 1. Do not use more than 100 mg of bot­ tube in demineralized water before proceeding tom material or severe bumping and loss of to the next sample. Treat each succeeding sam­ selenium may occur during the subsequent ple, blank, and standard in a like manner. digestion of the sample. 6.2 Prepare, in 300-mL fleakers, a blank and 7. Calculations sufficient standards containing from 0.1 to 2.0 7.1 Determine the micrograms of selenium jtg Se by diluting 1.0- to 20.0-mL portions of in each sample from a plot of absorbances of selenium standard solution III. Dilute each to standards. Exact reproducibility is not approx 100 mL. 6.3 To each fleaker add 1 drop methyl obtained, and an analytical curve must be orange, 0.5 mL CaCl2 solution, and a boiling prepared with each set of samples. chip or several glass beads. 7.2 Determine the concentration of dis­ 6.4 To the fleakers containing the blank and solved or total selenium in each sample as standards, add 0.5 mL O.lAf HC1. follows: 6.5 To the fleakers containing the samples, titrate with 0.1M HC1 until the indicator shows 1,000 Se X ^g Se in sample a distinct red color and then add 0.5 mL excess mL sample (NOTE 2). NOTE 2. If the water or water-suspended sedi­ 7.3 To determine the concentration of total ment samples have been acidified either at the suspended selenium, subtract dissolved- time of collection or in the laboratory, titrate with 2Af NaOH until the indicator shows a selenium concentration from total-selenium con­ distinct yellow-orange color and then continue centration. with paragraph 6.5. When the presence of in­ 7.4 Determine the concentration of selenium terferences makes it impossible to adjust the in air-dried bottom-material samples as follows: pH with use of methyl orange, use a pH meter for this adjustment. /ig Se in sample 6.6 Add 3 drops KMnO4 solution to each Se fleaker and heat to boiling on a hotplate, adding wt of sample (g) KMnO4 as required to maintain a purple tint. If a precipitate of MnO2 forms at this point, it 8. Report will have no adverse effect. 8.1 Report selenium, dissolved (01145), total 6.7 After the volume has been reduced to ap­ (01147), and suspended-total (01146), concentra­ prox 50 mL, add 2 mL 0.1M NaOH; evaporate tions as follows: less than 100 /ig/L, nearest 402 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Number of Mean Relative standard deviation microgram per liter; 100 ptg/L and above, two laboratories _____(percent)_____ significant figures. 5 2.0 0 8.2 Report selenium, total-in-bottom- 7 3.6 27 material (01148), concentrations as follows: less 3 9.0 29 than 100 ptg/g, to the nearest microgram per 5 19 47 gram; 100 /tg/g and above, two significant 5 42 50 figures. 9.3 It is estimated that the percent relative standard deviation for total and suspended 9. Precision selenium and for total selenium in bottom 9.1 Precision for dissolved selenium for 14 material will be greater than that reported for samples within the range of 2 to 42 pig/L may dissolved selenium. be expressed as follows: 9.4 Precision for total selenium expressed in terms of the percent relative standard deviation for one water-suspended sediment mixture is as 0.484 X- 1.447 follows: Number of Mean Relative standard deviation laboratories QtQ/L) _____(percent)_____ where 6.5 34 ST = overall precision, micrograms per liter, and References X = concentration of selenium, micrograms Freeman, H. C., and Uthe, J. F.f 1974, An improved hydride per liter. generation apparatus for determining arsenic and The correlation coefficient is 0.9412. selenium by atomic absorption spectrometry: Atomic Absorption Newsletter, v. 13, p. 75-6. 9.2 Precision for dissolved selenium for five Lansford, Myra, McPherson, E. M., and Fishman, M. J., of the 14 samples expressed in terms of percent 1974, Determination of selenium in water: Atomic Ab­ relative standard deviation is as follows: sorption Newsletter, v. 13, p. 103-5. Selenium, atomic absorption spectrometric, hydride, automated

Parameters and Codes: Selenium, dissolved, 1-2667-85 (ftgIL as Se): 01145 Selenium, total, I-4667-85 (/ig/L as Se): 01147 Selenium, suspended total, I-7667-85 (/ig/L as Se): 01146 Selenium, total-in-bottom-material, dry wt, I-6667-85 0*g/g as Se): 01148

1. Application using a stannous chloride-potassium iodide mix­ 1.1 This method may be used to analyze ture and is further converted to selenium water and water-suspended sediment contain­ hydride with sodium borohydride. The selenium ing at least 1 /ig/L of selenium. Samples contain­ hydride gas is stripped from the solution by a ing more than 15 /xg/L need to be diluted. stream of nitrogen gas and conveyed to a tube 1.2 Suspended total selenium is calculated furnace placed in the optical path of an atomic by subtracting dissolved selenium from total absorption spectrometer, where it is decom­ selenium. posed to atomic selenium. The optical absorb- 1.3 Water-suspended sediment may be ance is measured and related to the selenium analyzed by this procedure after each sample concentration in the original sample. has been thoroughly mixed by vigorous shak­ 2.2 For additional information on the deter­ ing and a suitable portion has been rapidly mination of selenium in water, see Goulden and withdrawn from the mixture. Suspended- Brooksbank (1974), and Pierce and others sediment concentrations must be less than 2.6 (1976). g/L. Greater concentrations can cause less than 100-percent recovery of selenium from some 3. Interferences organic selenium compounds such as diphenyl 3.1 No interferences have been observed selenide. with the decomposition of selenium hydride in 1.4 This method may be used to analyze bot­ the tube furnace and its subsequent tom material containing at least 1 /*g/g of measurement. selenium. For samples containing more than 5.6 3.2 Goulden and Brooksbank (1974) /*g/g, use less sediment. The amount of sediment reported no significant interferences in the that can be used is limited to 40-mg dry weight digestion, reduction, and selenium hydride- because, if greater amounts are used, selenium generation processes. will not be recovered completely from some 3.3 Pierce and Brown (1976) reported inter­ organic selenium compounds such as diphenyl ferences from trace elements commonly found selenide. in water at concentrations greater than 300 1.5 Bottom material may be analyzed by /tg/L when sodium borohydride was introduced this procedure after it has been prepared as in the sample stream before hydrochloric acid. directed in method 1-0520. 3.4 Nitric acid in excess of that usually added as a preservative in water and water- 2. Summary of method suspended sediment samples, is reported to 2.1 Organic selenium-containing compounds cause erratic results. are decomposed by hydrochloric acid- potassium persulfate digestion. The selenium so 4. Apparatus liberated, with inorganic selenium originally 4.1 Atomic absorption spectrometer and present, is then reduced to the tetravalent state recorder.

403 404 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Refer to the manufacturer's manual to optimize Nitrogen inlet instrument for the following: Tube furnace Grating ———————— Ultraviolet 0 50-mm ID Wavelength counter - 196.0 nm Tygon tubing Source (electrodeless Rubber stopper Ball and socket joint discharge lamp) —— Selenium (No 0) 4.2 Autotransformer, variable: Superior Power- stat type 3 PN 1010 or equivalent. TWo are 15-mm ID - needed, one for the stripping column and one for the tube furnace. 4.3 Dri-bath, 0-110°C. Thermolyne Model DB16525 or equivalent. £ 4.4 Pyrometer, portable, 0-1200 °C. Thermo­ 5 lyne Model PM-20700 or equivalent. 4.5 Stripping-condensing column, Pyrex, packed with 3- to 5-mm Pyrex beads (fig. 41). Wrap the stripping column with heating tape and cool the condensing column with water. The 5-mm ID - Waste nitrogen gas flow rate is adjusted for maximum E sensitivity by analyzing a series of identical 8 standards. A flow rate of approximately 200 mL/min has been found satisfactory. 4.6 Tube furnace, quartz, 10-mm IDXIOO-mm Figure 41—Stripping-condensing column and quartz-tube length with a quartz eyelet at each end of tube furnace to anchor nickel-chrome wire and tube fused at the center with a 2-mm ID quartz tuba Wrap the 5.6 Selenium standard solution II, 1.00 tube furnace with a 5.5 m (18 ft) of 26-gauge, mL = 10.0 Mg Se: Dilute 5.00 mL selenium stand­ nickel-chrome wire and cover with asbestos doth. ard solution I and 1 mL concentrated HNO3 (sp Mount lengthwise in the optical path of the gr 1.41) to 500 mL with demineralized water. atomic absorption spectrometer. Discard after 3 months. 4.7 Tkchnicon AutoAnalyzer II, consisting of 5.7 Selenium standard solution HI, 1.00 sampler, manifold, proportioning pump, and mL = 0.10 /ig Se: Dilute 5.00 mL selenium stand- heating bath. aid solution II and 1 mL concentrated HNO3 (sp Heating bath temperature - 95 °C gr 1.41) to 500 mL with demineralized water. Cam ————————————— 30 (1/2) Prepare fresh weekly. 4.8 Test tubes, graduated, 25-mL capacity, 5.8 Selenium working standards'. Prepare dai­ Pyrex 9802 or equivalent. ly a blank and 100 mL each of a series of selenium working standards containing 0.15 mL 5. Reagents concentrated HNOg by appropriate quantitative 5.1 Hydrochloric add, concentrated (sp gr 1.19). dilution of selenium standard solution III. 5.2 Nitrogen gas, N2. 5.3 Potassium iodide solution, 20 g/L: Dissolve Selenium standard solution II Selenium concentration 20 g KI in demineralized water and dilute to 1 L. (MQ/U 5.4 Potassium persulfate solution, 20 g/L: 1.0 1 2.0 2 Dissolve 20 g K2S2O8 in demineralized water 5.0 5 and dilute to 1 L. 10.0 10 5.5 Selenium standard solution 1, 1.00 mL = 15.0 15 1.00 mg Se: Dissolve 2.3928 g Na2SeO4 in demineralized water. Add 1 mT. concentrated 5.9 Sodium borohydride solution 0.5 g/L: HNO3 (sp gr 1.41) and dilute to 1,000 mL with Dissolve 0.5 g NaBH4 and 4 g NaOH in demineralized water. demineralized water and dilute to 1 L. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 405 5.10 Stannous chloride solution, 1.3 g/L: 6.4 Add a boiling stone and place the test Dissolve 1.6 g SnCl2*2H2O in 1 L concentrated tubes in a dri-bath at a temperature of 100 °C, HC1 (sp gr 1.19). This solution is unstable. and boil each tube for a minimum of 15 min but Prepare fresh daily. no longer than 20 min (NOTE 1). Cool the solu­ tion to room temperature, dilute to 17.0 mL 6. Procedure with demineralized water, and mix (NOTE 2). 6.1 Follow instructions in paragraph 6.1.1 NOTE 1. Alternatively, the solutions may be for waters or water-suspended sediment mix- digested in an autoclave. After addition of HC1 tures and in paragraph 6.1.2 for bottom and K2S2O8, autoclave solutions for 20 min at materials. 15 psi pressure. Cool the solutions and add 3.0 6.1.1 Pipet a volume of well-mixed sample con­ mL oxalic acid solution (dissolve 35 g oxalic acid taining less than 0.225 fig Se (15 mL max) into dihydrate in demineralized water and dilute to a 25-mL graduated test tube. 1 L). Autoclave solutions for an additional 20 6.1.2 Weigh 40 mg or less of bottom-material min at 15 psi pressure. Cool solutions and dilute sample (0.225 /*g Se max), transfer into a 25 mL to 17.0 mL with demineralized water. Proceed graduated test tube, and add 15 mL deminer- to paragraph 6.5. alized water. NOTE 2. A different volume may be used as 6.2 Pipet 15 mL blank and a complete set of long as the same volumes of standards and standard solutions (sufficient to satisfy the re­ samples are used in each run. quirements of 6.8) containing from 1.0 to 15.0 6.5 Set up manifold (fig. 42) (NOTE 3). figlL into 25-mL graduated test tubes. NOTE 3. Change the acid flex tubing weekly. 6.3 To each tube, add 1.5 mL K2S2O8 so­ 6.6 Set stripping-column and tube-furnace lution and 0.3 mL concentrated HC1, and temperatures by applying necessary voltage as mix. follows:

Heating bath 20ft coil

20-turncoil 10-turncoil 0.110in Sample 3.90mL/min

0.056in Air Sampler 4 30/h 1.20mL/min 1/2cam 0.073in Stannous chloride^ 1.85mL/min

0.040 in Potassium iodide 0.60mL/min O.IOOin Sodium borohydride 20-turncoil 3.40mL/min To Sampler 4 wash ^ 0.110in Water receptacle 3.90mL/min

iRed acidflex tubing Heating bath 40ft coil Proportioning pump Figure 42.—Selenium, hydride manifold 406 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Stripping-column tem­ from the third tube for the reading on the most perature ————— 75 °C (about 36V) concentrated standard (the first two tubes Tube-furnace tempera­ usually give low readings). ture ———————— 800 °C (about 47 V) 7.2 Determine the concentration of dis­ Stripping column temperatures higher than solved or total selenium in each sample by com­ 75 °C cause the peak to split. Monitor the tube- paring its peak height to the analytical curve. furnace temperature using a portable pyrometer Any baseline drift that may occur must be with the thermocouple placed in the middle of taken into account when computing the height the tube, and monitor the waste-stream temper­ of a sample or standard peak. ature using a laboratory thermometer. Adjust 7.3 To determine the concentration of sus­ voltages on the autotransformers as necessary pended total selenium, subtract dissolved- to control these temperatures. selenium concentration from total-selenium con­ 6.7 Initially, feed all reagents through the centration. system using demineralized water in the sam­ 7.4 To determine micrograms per gram of ple line and allow the baseline to stabilize. selenium in bottom-material samples, first 6.8 Prepare the sample tray as follows: (1) determine the micrograms per liter of selenium In the first tray, place three tubes of the most in each sample as in paragraph 7.2; then: concentrated standard followed by one tube each of the remaining standards and blank, in Se X 0.015 L decreasing concentrations; (2) place individual Se in /xg/g = standards of differing concentrations in every wt of sample (g) eighth position of the remainder of this and subsequent trays; (3) fill the remainder of each 8. Report sample tray with unknown samples. 8.1 Report selenium, dissolved (01145), total 6.9 When the baseline stabilizes, remove the (01147), and suspended-total (01146), concentra­ sample line from the demineralized wash solu­ tions as follows: less than 10 jig/L, nearest jtg/L; tion and begin analysis. 10 jxg/L and above, two significant figures. 6.10 With a 5-mV recorder, 10 /tg/L of 8.2 Report selenium, total-in-bottom-mate­ selenium produces a peak approx 60 percent of rial (01148), concentrations as follows: less than full scale. If the sensitivity drops by 30 percent 10 pig/g» nearest pglg; 10 /tg/g and above, two or more, replace or treat the tube furnace (cell) significant figures. by one of the following methods: 6.10.1 Soak the tube furnace for 30 minutes 9. Precision in 1:1 water-hydrofluoric acid solution and rinse 9.1 Analysis of four samples for dissolved with demineralized water. selenium five times each by one operator 6.10.2 Grind the cell with silicon carbide as resulted in mean values of 3.3, 4.2, 6.4, and 8.5 follows: Mount cell with suitable cushioning in fig/L and standard deviations of 0.1, 0.4, 0.2, a 3/4-inch chuck on a slowly-revolving shaft. and 0.1 /tg/L, respectively. Wet inside of cell and apply grinding compound 9.2 Precision for dissolved selenium also such as commercial auto-valve-grinding com­ may be expressed in terms of percent relative pound. Using a standard speed drill and an standard deviation as follows: aluminum oxide grinding wheel suitably re­ Number of Mean Relative standard deviation duced in diameter to give adequate clearance, replicates (M9/L) _____(percent)_____ and plenty of water, begin grinding cell with a 5 3.3 3 steady movement from inside to outside of cell. 5 4.2 10 5 6.4 3 Grind one-half of cell at a time and regrind if 5 8.5 1 necessary to achieve an even frosting. 9.3 Analysis of four samples for total 7. Calculations selenium five times each by one operator 7.1 Prepare an analytical curve by plotting resulted in mean values of 2.0, 8.6, 10.4, and the height of each standard peak versus its 20.0 /tg/L and standard deviations of 0.5, 0.2, respective selenium concentration; use the value 0.3, and 0.9 jig/L, respectively. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 407

Number of Mean Relative standard deviation 9.4 Precision for total selenium also may be replicates _____(percent)_____ expressed in terms of percent relative standard 5 1.4 21 deviation as follows: 5 1.7 6 5 2.4 8 Number of Mean Relative standard deviation 3 replicates _____(percent)_____ 5 3.4 5 2.0 25 5 8.6 2 References 5 10.4 3 5 20.0 4 Goulden, P. D., and Brooksbank, Peter, 1974, Automated atomic absorption determination of arsenic, antimony, and selenium in natural waters: Analytical Chemistry, 9.5 Analysis of four bottom-material v. 46, p. 1431-6. samples for selenium five times each by one Pierce, F. D., and Brown, H. R., 1976, Inorganic interference operator resulted in mean values of 1.4,1.7, 2.4, study of automated arsenic and selenium determination and 3.4 pglg and standard deviations of 0.3,0.1, with atomic absorption spectrometry: Analytical 0.2, and 0.1 /ig/g, respectively. Chemistry; v. 48, p. 693-5. 9.6 Precision for selenium in bottom-mate­ Pierce, F. D., Lamoreaux, T. C., Brown, H. R., and Fraser, R. S., 1976, An automated technique for the sub- rial samples also may be expressed in terms microgram determination of selenium and arsenic in sur­ of percent relative standard deviation as face waters by atomic absorption spectroscopy: Applied follows: Spectroscopy, v. 30, p. 38-42.

Selenium, total-in-sediment, atomic absorption spectrometric, hydride

Parameter and Code: Selenium, total, 1-5475-85 (mg/kg as Se): none assigned

2. Summary of method hotplate at 200 °C. Selenium is determined on A sediment sample is dried, ground, and the resulting solution by atomic absorption homogenized. The sample is digested with a spectrometry. See method 1-5475, metals, combination of nitric, hydrofluoric, and per­ minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a spectrometric, hydride. 409

Silica, atomic absorption spectrometric, direct

Parameter and Code: Silica, dissolved, 1-1702-85 (mg/L as SiO2): 00955

1. Application Oxidant ———————— Nitrous oxide This method may be used to analyze water Fuel —————————— Acetylene containing at least 0.5 mg/L of silica. Samples Type of flame ———— Fuel-rich containing more than 35 mg/L need either to be diluted or to be read on a less expanded scale. 5. Reagents The sensitivity of the determination is depend­ 5.1 Silica standard solution, 1.00 mL = ent on the amount of acetylene remaining in the 0.500 mg SiO2: Dissolve 1.7655 g sodium cylinder. When a full cylinder is used (290 psi), metasilicate (Na2SiO3-5H2O) in demineralized a sensitivity of about 0.40 mg SiO2 per scale water and dilute to 1,000 mL. Store in a plastic division may be expected. However, when a bottle. near-empty cylinder is used (for example, 50 5.2 Silica working standards: Prepare a psi), a sensitivity of only about 0.55 mg SiO2 series of at least six working standards contain­ per scale division is observed. The significant ing from 0.5 to 35 mg/L of silica by appropriate amount of acetone vapor present in the last dilution of silica standard solution. Store in acetylene to be withdrawn from a cylinder plastic bottles. decreases the sensitivity for silica in the nitrous oxide-acetylene flame. 6. Procedure While aspirating the blank use the automatic 2. Summary of method zero control to set the digital display to read zero Silica is determined by atomic absorption concentration. While aspirating standards use the spectrometry by direct aspiration of the sam­ automatic concentration control to set the digital ple into a nitrous oxide-acetylene flame without display to read the concentrations of standards. preconcentration or pretreatment of the sample. Use at least; six standards. Calibrate the instru­ ment each time a set of samples is analyzed and 3. Interferences check calibration at reasonable intervals. None of the substances commonly occurring in natural water interfere with this method. 7. Calculations Determine the milligrams per liter of dis­ 4. Apparatus solved silica (as SiO2) in each sample from the 4.1 Atomic absorption spectrometer digital display or printer output while equipped with electronic digital readout and aspirating each sample. Dilute those samples automatic zero and concentration controls. containing concentrations of silica that exceed 4.2 Refer to the manufacturer's manual to the working range of the method and multiply optimize instrument for the following: by the proper dilution factors. Grating ———————— Ultraviolet i Wavelength ————— 251.6 nm 8. Report Source (hollow-cathode Report silica, dissolved (00955), concentra­ lamp) ———————— Silica tions as follows: less than 10 mg/L, one decimal; Burner ———————— Nitrous oxide 10 mg/L and above, two significant figures.

411 412 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 9. Precision the 20 samples expressed in terms of the per­ 9.1 The standard deviation for dissolved cent relative standard deviations is as follows: silica within the range of 1.10 to 16.5 mg/L for 20 samples was found to be independent of con­ Number of Relative standard deviation centration. The 95-percent confidence interval laboratories (mq/L) _____(percent)_____ for the average standard deviation of 1.49 mg/L 3 3.83 21 8 10.4 12 ranged from 1.30 to 1.75 mg/L. 7 16.4 8 9.2 Precision for dissolved silica for four of 4 16.5 4 Silica, atomic emission spectrometric, ICP I I Parameter and Code: Silica, dissolved, 1-1472-85 (mg/L as SiO2): 00955

2. Summary of method method utilizing an induction-coupled argon Silica is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 413

Silica, colorimetric, molybdate blue

Parameter and Code: Silica, dissolved, 1-1700*85 (mg/L as SiO2j: 00955

1. Application sample. The addition of disodium dihydrogen This method may be used to analyze water ethylenediamine tetraacetate (Na2EDTA) containing from 0.1 to 100 mg/L of silica. eliminates the effect of high concentrations of Samples containing more than 100 mg/L need iron, and also complexes calcium and prevents to be analyzed by standard gravimetric pro­ precipitation of calcium sulfite. cedures (American Society for Testing and Materials, 1984; Kolthoff and others, 1969). 4. Apparatus 4.1 Spectrometer for use at 700 nm. 2. Summary of method 4.2 Refer; to the manufacturer's manual to 2.1 Silica in solution as silicic acid or silicate optimize instrument. has the property of reacting with ammonium molybdate in an acid medium to form the yellow silicomolybdate complex. The silicomolybdate 5. Reagents 5.1 Ammonium molybdate solution: 49 g/L: complex is then reduced by sodium sulfite to Dissolve 52 g (NH4)6Mo7O24*4H2O in water, form the molybdate blue color. The silicomolyb­ date complex may form in water as alpha and adjust the pH to between 7 and 8 with 10M beta polymorphs (Strickland, 1952), which have NaOH, and dilute to 1 L with demineralized absorbance maxima at different wavelengths. water. Filter through 0.45-ptm membrane filter In order to favor the development of the beta if necessary. form, the pH of the reaction mixture is reduced 5.2 Hydrochloric acid, l.OM: Mix 88 mL con­ below 2.5 (Govett, 1961). centrated HC1 (sp gr 1.19) with demineralized 2.2 The possibility of having unreactive water and dilute to 1 L. silica is greater in water containing high con­ 5.3 Silica standard solution I, 1.00 mL = centrations of silica than in water containing 0.500 mg SiO2: Dissolve 1.7655 g sodium low concentrations of silica. When significant metasilicate|(Na2SiO3-5H2O) in demineralized amounts of unreactive silica are known or water. Store in a plastic bottle. suspected to be present, a 1-h digestion of 5.4 Silica standard solution II, 1.00 mL = 50-mL sample with 5.0 mL of l.OM NaOH is 0.005 mg SiO2: Dilute 10.0 mL silica standard suggested to make all the silica available for solution I to 1,000 mL with demineralized reaction with the molybdate reagent. water. Store in a plastic bottle. 5.5 Na^DTA solution, 10 g/L: Dissolve 10 3. Interferences g Na2EDTA in demineralized water and dilute Phosphate produces a similar molybdate com­ to 1 L. plex under certain pH conditions. In the follow­ 5.6 Sodium hydroxide solution, 10M: ing determination, tartaric acid is added to Dissolve 400 g NaOH in demineralized water suppress phosphate interference. Hydrogen sul- and dilute to 1 L. fide and ferric and ferrous iron apparently in­ 5.7 Sodium sulfite solution, 170 g/L: terfere with the determination. Hydrogen Dissolve 170 g Na2SO3 in demineralized water sulfide may be removed by boiling an acidified and dilute to 1 L. 415 416 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.8 Tartaric acid solution, 100 g/L: Dissolve 9. Precision 100 g H2C4H4O6 in demineralized water and 9.1 Precision for dissolved silica for 35 dilute to 1 L. samples within the range of 2.15 to 24.4 mg/L may be expressed as follows: 6. Procedure 6.1 Pipet a volume of sample containing less than 0.5 mg SiO2 (10.0 mL max) into a 50-mL where beaker, and adjust the volume to 10.0 mL. ST = overall precision, milligrams per liter, 6.2 Pipet a demineralized water blank and and sufficient standards into 50-mL beakers, and ad­ X = concentration of silica, milligrams per just the volume of each to 10.0 mL. liter. 6.3 Add to each solution, with stirring, 5.0 The correlation coefficient is 0.8053. mL l.OAf HC1, 5.0 mL Na2EDTA solution, and 9.2 Precision for dissolved silica for four of 5.0 mL ammonium molybdate solution. the 35 samples expressed in terms of the per­ 6.4 After 5 min add 5.0 mL tartaric acid cent relative standard deviation is as follows: solution and mix. 6.5 Add 10.0 mL Na2SO3 solution and mix. Number of Mean Relative standard deviation 6.6 Allow to stand approx 30 min. The col­ laboratories (mg/L) _____(percent)_____ or is stable for several hours. 19 2.15 16 6.7 Determine the absorbance of each test 11 9.08 5 6 10.2 15 sample and standards against the blank. 24 24.4 7

7. Calculations 7.1 Determine milligrams of silica in each References sample from a plot of absorbances of standards. 7.2 Determine the concentration of dis­ American Society for Testing and Materials, 1984, Annual book of ASTM standards, section llt water: Philadel­ solved silica in milligrams per liter as follows: phia, v. 11.01, p. 613-8. Govett, G. J. S., 1961, Critical factors in the colorimetric 1,000 determination of silica: Analytica Chimica Acta, v. 25, SiO2 (mg/L)= Xmg SiO2 in sample. p. 69-80. mL sample Kolthoff, I. M.t Sandell, E. B., Meehan, E. J., and Brucken- stein, S., 1969, Quantitative chemical analysis, (4th ed): New York, Macmillan, 1199 p. 8. Report Strickland, J. D. H., 1952, The preparation and properties Report silica, dissolved (00955), concentra­ of silicomolybdic acid; I. The properties of alpha tions as follows: less than 10 mg/L, one decimal; silicomolybdic acid: American Chemical Society Jour­ 10 mg/L and above, two significant figures. nal, v. 74, p. 862-7. Silica, colorimetric, molybdate blue, automated-segmented flow

Parameter and Code: Silica, dissolved, 1-2700-85 (mg/L as SiO2): 00955

1. Application 4. Apparatus This method may be used to determine con­ 4.1 Technicon AutoAnalyzer II, consisting centrations of silica in surface, domestic, and in­ of sampler, cartridge manifold, proportioning dustrial water in the range from 0.1 to 60 mg/L. pump, colorimeter, voltage stabilizer, recorder, Two analytical ranges are used: from 0.1 to 6.0 and printer. mg/L and from 1.0 to 60 mg/L. 4.2 With this equipment the following operating conditions have been found satisfac­ 2. Summary of method tory for the range from 0.1 to 60 mg/L: 2.1 Silica reacts with molybdate reagent in Absorption cell ——————— 15 mm acid media to form a yellow silicomolybdate Wavelength ———————— 660 nm complex. This complex is reduced by ascorbic Cam ———————————— 60/h(6/l) acid to form the molybdate blue color. The silicomolybdate complex may form either as an 5. Reagents alpha or beta polymorph or as a mixture of both. 5.1 Ammonium molybdate solution, 9.4 g/L: Because the two polymorphic forms have Dissolve 5 g (NH4)6Mo7O24-4H2O in 0.05M absorbance maxima at different wavelengths, H2SO4 and dilute to 500 mL with 0.05AT the pH of the mixture is kept below 2.5, a con­ H2SO4. Filter and store in an amber plastic dition that favors formation of the beta container. polymorph (Govett, 1961; Mullen and Riley, 5.2 Ascorbic acid solution, 17.6 g/L: 1955; Strickland, 1952). Dissolve 17.6 g ascorbic acid in 500 mL demin- 2.2 The possibility of having "unreactive" eralized water containing 50 mL acetone. Dilute silica is greater in water containing high con­ to 1 L with demineralized water. Add 0.5 mL centrations of silica than in water containing Levor IV solution. The solution is stable for 1 low concentrations of silica. When significant week if stored at 4°C. amounts of unreactive silica are known or 5.3 Levor IV solution: Technicon No. suspected to be present, a 1-h digestion of a 21-0332 or equivalent. 50-mL sample with 5.0 mL of l.OAf NaOH is 5.4 Oxalic acid solution, 50 g/L: Dissolve 50 suggested as a means of making all the silica g oxalic acid in demineralized water and dilute available for reaction with the molybdate to 1 L. reagent. 5.5 Silica standard solution, 1.00 mL = 0.500 nag SiO2: Dissolve 1.7655 g sodium 3. Interferences metasilicate (Na2SiO3*5H2O) in demineralized Interference from phosphate, which forms a water and dilute to 1,000 mL. Store in a plastic phosphomolybdate complex, is suppressed by bottle. the addition of oxalic acid. Hydrogen sulfide 5.6 Silica working standards: Prepare a must be removed by boiling the acidified sam­ blank and 1,000 mL each of a series of silica ple prior to analysis. Large amounts of iron working standards by appropriate quantitative interfere. dilution of silica standard solution as follows:

417 418 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Silfca standard solution Silica concentration tray, beginning with the most concentrated (ml) (mg/L) standard. Place individual standards of differ­ oo 00 ing concentrations in approximately every .5 0.25 1.0 .5 eighth position of the remainder of this and 2.0 1.0 subsequent sample trays. Fill remainder of each 12.0 6.0 20.0 10 tray with unknown samples. 40.0 20 6.5 Begin analysis. When the peak from the 80.0 40 most concentrated working standard (6.0 or 60 120.0 60 mg/L) appears on the recorder, adjust the STD 5.7 Sulfuric acid, 0.05M: Cautiously add 2.8 CAL control until the flat portion of the curve mL concentrated H2SO4 (sp gr 1.84) to demin- reads full scale. eralized water and dilute to 1 L. 7. Calculations 6. Procedure 7.1 Prepare an analytical curve by plotting 6.1 Set up manifold (fig. 43). the height of each standard peak versus its 6.2 Allow colorimeter and recorder to warm respective silica concentration. up for at least 30 min, 7.2 Compute the concentration of dissolved 6.3 Adjust baseline to read zero scale divi­ silica in each sample by comparing its peak sions on the recorder with all reagents, but with height to the analytical curve. Any baseline demineralized water in the sample line. drift that may occur must be taken into account 6.4 Place a complete set of standards and a when computing the height of a sample or blank in the first positions of the first sample standard peak.

20-turn coils 0.030 in Air 22-turn coil 0.32 mL/min 0.035 in Molybdate reagent 0.42 mL/min 0.025 in Sample 0.23 mL/min

0.030 in °»lic acid Sampler 4 0.32 mL/min GO/ h 0.035 in Ascorbic acid 6/1 cam Colorimeter 0.42 mL/min 660 nm Waste To sampler 4 Water 15-mmcell wash - 0.073 in 2.00 mL/min receptacle 0.045 in Waste 0.80 mL/min Recorder Proportioning pump

Figure 43.—Silica, molybdate manifold METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 419

8. Report Number of Mean Relative standard deviation laboratories (mgJL) _____(percent)_____ Report silica, dissolved (00955), concentra­ 5 4.70 7 tions as follows: less than 10 mg/L, nearest 0.1 8 8.95 23 mg/L; 10 mg/L and above, two significant 6 10.6 6 figures. 5 17.4 7

9. Precision References 9.1 The standard deviation for dissolved silica within the range of 4.70 to 17.4 mg/L for Govett, G. J. S., 1961, Critical factors in the colorimetric determination of silica: Analytica Chimica Acta, v. 25, 20 samples was found to be independent of con­ p. 69-80. i centration. The 95-percent confidence interval Mullen, J. B., and Riley, J. P., 1955, The colorimetric deter­ for the average standard deviation of 1.10 mg/L mination of silicate with special reference to sea and ranged from 0.97 to 1.26 mg/L. natural waters: Analytica Chimica Acta, v. 12, 9.2 Precision for dissolved silica for four of p. 162-76! Strickland, J. D. H., 1952, The preparation and properties the 20 samples expressed in terms of the of silicomolybdic acid: I. The properties of alpha percent relative standard deviation is as silicomolybdic acid: American Chemical Society Jour­ follows: nal, v. 74, p. 862-7.

Silica, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Silica, total, 1-5473-85 (mg/kg as SiO2): nono assigned

2. Summary of method The resulting bead is dissolved in acidified, boil­ A sediment sample is dried, ground, and ing, demineralized water, and silica is determined homogenized. The sample is fused with a mixture by atomic absorption spectrometry. See method of lithium metaborate and lithium tetraborate in 1-5473, metals, major, total-in-sediment, atomic a graphite crucible in a muffle furnace at 1,000 °G absorption spectrometric, direct. 421

Silver, atomic absorption spectrometric, chelation-extraction

Parameters and Codes: Silver, dissolved, 1-1720-85 fcig/L as Ag): 01075 Silver, total recoverable, I-3720-85 (^g/L as Ag): 01077 Silver, suspended recoverable, I-7720-85 fcg/L as Ag): 01076

1. Application Oxidant ———————— Air 1.1 This method may be used to analyze Fuel —————————— Acetylene water, brines, and water-suspended sediment Type of flame ———— Oxidizing containing from 1 to 10 figIL of silver. Samples 4.3 Different burners may be used according containing more than 10 jig/L need to be diluted to manufacturers' instructions. or to be read on a less expanded scale. 1.2 Suspended recoverable silver is 5. Reagents calculated by subtracting dissolved silver from 5.1 Ammonium pyrrolidine dithiocarbamate total recoverable silver. (APDC) solution, 1 g/100 mL: Dissolve 1 g 1.3 Total recoverable silver in water-sus­ APDC in 100 mL demineralized water. Prepare pended sediment needs to undergo a prelimi­ fresh daily. nary digestion-solubilization by method 1-3485 5.2 Citric acid-sodium citrate buffer solution: before being determined. Dissolve 126 g citric acid monohydrate and 44 g sodium citrate dihydrate in demineralized 2. Summary of method water and dilute to 1 L with demineralized Silver is determined by atomic absorption water. See NOTE 3 before preparation. spectrometry following chelation with am­ 5.3 Methyl isobutyl ketone (MIBK). monium pyrrolidine dithiocarbamate (APDC) 5.4 Silver standard solution 1, 1.00 mL = 100 and extraction with methyl isobutyl ketone j*g Ag: Crush approx 2 g of AgNO3 crystals and (MIBK). The extract is aspirated into an air- dry to constant mass at 40 °C. Dissolve 0.1575 acetylene flame of the spectrometer. g AgNO3 in demineralized water and dilute to 1,000 mL. Store in amber bottla 3. Interferences 5.5 Silver standard solution II, 1.00 Concentrations of iron greater than 25,000 mL = 1.00 /iig Ag: Dilute 10.0 mL silver stand­ /ig/L interfere by suppressing the silver ab­ ard solution I and 1.0 mL concentrated HNO3 sorption. (sp gr 1.41) to 1,000 mL with demineralized water. This solution is used to prepare working 4. Apparatus standards at the time of analysis. Store in 4.1 Atomic absorption spectrometer amber bottle. equipped with electronic digital readout and 5.6 Potassium hydroxide, 10M: Dissolve 56 automatic zero and concentration controls. g KOH in demineralized water, cool, and dilute 4.2 Refer to the manufacturer's manual to to 100 mL. optimize instrument for the following: 5.7 Potassium hydroxide, 2.5M: Dissolve 14 Grating ———————— Ultraviolet g KOH in demineralized water and dilute to 100 Wavelength ————— 328.1 nm mL(NOTE!l). Source (hollow-cathode NOTE 1. Alternatively, a 2.5M NH4OH solu­ lamp) ———————— Silver tion may te used. Add 167 mL concentrated 423 424 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS NH4OH (sp gr 0.90) to 600 mL demineralized silver that exceed the working range of the water. Cool and dilute to 1 L. method; repeat the chelation-extraction and 5.8 Water, acidified: Add 1.5 mL concen­ multiply by the proper dilution factors. trated HNO3 (sp gr 1.41) to 1 L of demineral­ 7.2 To determine micrograms per liter of ized water. suspended recoverable silver, subtract dissolved-silver concentration from total- 6. Procedure recoverable-silver concentration. 6.1 Clean all glassware used in this deter­ mination with warm, dilute nitric acid (1+9) 8. Report and rinse with demineralized water immediate­ Report silver, dissolved (01075), total-recov­ ly before use. erable (01077), and suspended-recoverable 6.2 Pipet a volume of sample solution con­ (01076), concentrations as follows: less than 10 taining less than 1.0 jtg Ag (100 mL max) into /xg/L, nearest microgram per liter; 10 /tg/L and a 200-mL volumetric flask, and adjust the above, two significant figures. volume to approx 100 mL. 6.3 Prepare a blank of acidified water and 9. Precision sufficient standards, and adjust the volume of 9.1 Precision for dissolved silver for 16 each to approx 100 mL with acidified water. samples within the range of 1.5 to 13.6 6.4 With a pH meter, adjust the pH of each may be expressed as follows: solution to 2.4 with 2.5ATKOH (NOTES 2 and 3). S = 0.478X-1.29 NOTE 2. For water-suspended sediment samples that have been digested, add 1 to 2 mL 10M KOH or concentrated NH4OH (sp gr 0.90) where before pH adjustment. ST = overall precision, micrograms per liter, NOTE 3. If an automated titration system is and used to adjust the pH, add 2.5 mL citric acid- X — concentration of silver, micrograms per sodium citrate buffer solution prior to pH ad­ liter. justment. This will prevent over-shooting the The correlation coefficient is 0.7681. end point in poorly buffered samples. 9.2 Precision for dissolved silver for five of 6.5 Add 2.5 mL APDC solution and shake the 16 samples expressed in terms of the per­ for 3 min. cent relative standard deviation is as follows:

6.6 Add 10.0 mL MIBK and shake vigorous­ Number of Relative standard deviation ly for 3 min. laboratories (MO/L) _____(percent)_____ 6.7 Allow the layers to separate and add 4 1.5 40 demineralized water until the ketone layer is 5 2.0 0 5 5.4 20 completely in the neck of the flask. 6 10.4 14 6.8 Aspirate the ketone layer of the blank to 5 13.4 26 set the automatic zero control. Use the automatic concentration control to set the con­ 9.3 It is estimated that the percent relative centrations of the standards. Use at least six standard deviation for total recoverable and standards. Calibrate the instrument each time suspended recoverable silver will be greater a set of samples is analyzed and check calibra­ than that reported for dissolved silver. tion at reasonable intervals. 9.4 Precision for total recoverable silver ex­ pressed in terms of the percent relative stan­ 7. Calculations dard deviation for one water-suspended 7.1 Determine the micrograms per liter of sediment is as follows: dissolved or total recoverable silver in each sam­ Number of Mean Relative standard deviation ple from the digital display or printer. Dilute laboratories QiO/L) _____(percent)_____ those samples containing concentrations of 8.1 30 Sodium, atomic absorption spectrpmetric, direct

Parameters and Codes: \ Sodium, dissolved, 1-1735-85 (mg/L as Na): 00930 Sodium, total recoverable, I-3735-85 (mg/L as Na): none assigned Sodium, recoverable-from-bottom-material, dry wt, I-5735-85 (mg/kg as Na): 00934

1. Application 4.2 Refer to the manufacturer's manual to 1.1 This method may be used to analyze at­ optimize instrument for the following: mospheric precipitation, water, brines, and Grating ———————— Visible water-suspended sediment. Wavelength ————— 588.8 nm 1.2 Two analytical ranges for sodium are in­ Source (hollow-cathode cluded: from 0.01 to 1.0 mg/L and from 0.10 to lamp) ———————— Sodium 80 mg/L. Sample solutions containing sodium Oxidant ———————— Air concentrations greater than 80 mg/L need to be Fuel —————————— Acetylene diluted. Type of flame ———— Oxidizing 1.3 This method may be used to analyze bot­ 4.3 The 50-mm (2-in.), flathead, single-slot tom material containing at least 10 mg/kg of burner, rotated 90°, allows working ranges of sodium. 0.01 to 1.0 mg/L and 0.1 to 80 mg/L. Different 1.4 Total recoverable sodium in water- burners may be used according to manufac­ suspended sediment needs to undergo turers' instructions. preliminary digestion-solubilization by method 1-3485, and recoverable sodium in bottom 5. Reagents material needs to undergo preliminary 5.1 Sodium standard solution, 1.00 mL = digestion-solubilization by method 1-5485 1.00 mg Na: Dissolve 2.542 g NaCl in deminer- before being determined. alized water and dilute to 1,000 mL. 5.2 Sodium working standards: Prepare a 2. Summary of method series of at least six working standards contain­ 2.1 Sodium is determined by atomic absorp­ ing either from 0.01 to 1.0 mg/L or from 0.10 tion spectrometry by direct aspiration of the to 80 mg/L sodium by appropriate dilutions of sample solution into an air-acetylene flame sodium standard solution. The preparation of (Fishman and Downs, 1966). an intermediate standard solution is desirable 2.2 The procedure may be automated by the when preparing working solutions of extreme addition of a sampler and either a strip-chart dilution. recorder or a printer. 6. Procedure 3. Interferences While aspirating the blank use the automatic None of the substances commonly occurring zero control to set the digital display to read zero in natural water interfere with this method. concentration. While aspirating standards use the automatic concentration control to set the 4. Apparatus digital display to read concentrations of stand­ 4.1 Atomic absorption spectrometer ards. Use at least six standards. Calibrate the in­ equipped with electronic digital readout and strument each time a set of samples is analyzed automatic zero and concentration controls. and check calibration at reasonable intervals. 425 426 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 7. Calculations where 7.1 Determine the milligrams per liter of ST = overall precision, milligrams per liter, dissolved or total recoverable sodium in each and sample from the digital display or printer while X — concentration of sodium, milligrams per aspirating each sample. Dilute those samples liter. containing sodium concentrations that exceed The correlation coefficient is 0.9461. the working range of the method and multiply 9.2 Precision for dissolved sodium for six of by the proper dilution factors. the 33 samples expressed in terms of the per­ 7.2 To determine milligrams per kilogram of cent relative standard deviation is as follows: sodium in bottom-material samples, first deter­ Number of Mean Relative standard deviation mine the milligrams per liter of sodium as in laboratories (mg/L) _____(percent)_____ paragraph 7.1, then: 22 0.20 35 36 2.76 13 25 15.4 6 35 56.0 5 mL original digest 31 96.9 5 mg/L Na X 19 222 6 Na (mg/kg) 1000 wt of sample (kg) 9.3 Precision for dissolved sodium within the range of 0.01 to 1.0 mg/L in terms of the per­ cent relative standard deviation by a single 8. Report operator is as follows: 8.1 Report sodium, dissolved (00930), and Number of Mean Relative standard deviation total-recoverable (none assigned), concentra­ replicates (mg/L) _____(percent)_____ tions as follows: less than 1.0 mg/L, two 8 0.009 26.5 8 .028 16.8 decimals; 1.0 to 10 mg/L, one decimal; 10 mg/L 8 .136 3.8 and above, two significant figures. 8 .540 1.0 8.2 Report sodium, recoverable-from- bottom-material (00934), concentrations as 9.4 It is estimated that the percent relative follows: less than 1,000 mg/kg, nearest 10 standard deviation for total recoverable sodium mg/kg; 1,000 mg/kg and above, two significant and for recoverable sodium from bottom ma­ figures. terial will be greater than that reported for dissolved sodium. 9. Precision 9.1 Precision for dissolved sodium for 33 Reference samples within the range of 0.20 to 222 mg/L Fishman, M. J., and Downs, S. C., 1966, Methods for may be expressed as follows: analysis of selected metals in water by atomic absorp­ tion: U.S. Geological Survey Water-Supply Paper ST = 0.046^ + 0.186 1540-C, p. 38-41. Sodium, atomic absorption spectrometric, direct-EPA ! I Parameter and Code: Sodium, total recoverable, 1-3736-85 (mg/L as Na): 00929

1* Application Grating ———————— Visible 1.1 This method may be used to analyze Wavelength ————— 588.8 nm water-suspended sediment containing from 0.1 Source (hollow-cathode to 80 mg/L of sodium. If the sodium concentra­ lamp) ——————— Sodium tion exceeds 80 mg/L, the sample solution needs Oxidant ——————— Air to be diluted. The method is very sensitive and Fuel ————————— Acetylene can be extended to much lower sodium concen­ Type of flame ———— Oxidizing trations. 4.3 The 50-mm (2-in.), flathead, single-slot 1.2 For ambient water, analysis may be burner, rotated 90 °, allows a range of 0.1 to 80 made on an aliquot of the acidified water- mg/L. Different burners may be used according suspended sediment sample. to manufacturers' instructions. 1.3 For all other water, including domestic and industrial effluent, the atomic absorption 5. Reagents procedure must be preceded by a digestion- 5.1 Hydrochloric acid 6M: Dilute 500 mL solubilization as specified below. In cases where concentrated HC1 (sp gr 1.19) to 1L with demin- the analyst is uncertain of the type of sample, eralized water. this procedure must be followed. 5.2 Hydrochloric acid, 0.3Af: Dilute 25 mL concentrated HC1 (sp gr 1.19) to 1L with demin- 2. Summary of method eralized water. 2.1 Sodium is determined by atomic absorp­ 5.3 Nitric acid, concentrated (sp gr 1.41). tion spectrometry by direct aspiration of the 5.4 Sodium standard solution, 1.00 filtered or digested and filtered sample into an mL = 1.00 mg Na: Dissolve 2.542 g NaCl in de- air-acetylene flame (Fishman and Downs, 1966). mineralized water and dilute to 1,000 mL. 2.2 Effluent samples must undergo a pre­ 5.5 Sodium working standards: Prepare a liminary nitric acid digestion followed by a series of at least six working standards contain­ hydrochloric acid solubilization. ing from 0.1 to 80 mg/L sodium by appropriate dilutions of sodium standard solution. The 3. Interferences preparation of an intermediate standard solu­ None of the substances commonly occurring tion is desirable when preparing working solu­ in natural water interfere with this method. tions of extreme dilution.

4. Apparatus 6. Procedure 4.1 Atomic absorption spectrometer 6.1 When analyzing samples of ambient equipped with electronic digital readout and waters, begin the analysis at step 6.9. automatic zero and concentration controls. 6.2 Transfer the entire sample to a beaker. 4.2 Refer to the manufacturer's manual to 6.3 Rinse the sample bottle with 3 mL con­ optimize instrument for the following: centrated HNO3 for each 100 mL of sample and

427 428 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS add to the beaker. Prepare a blank using 3 mL 7. Calculations concentrated HNO3 per 100 mL demineralized Determine the milligrams per liter of total water. recoverable sodium in each sample from the 6.4 Evaporate samples and blank to dryness digital display or printer while aspirating each on a hotplate, making sure the samples do not sample. Dilute those samples containing sodium boil. concentrations that exceed the working range 6.5 Cool and add an additional 3 mL concen­ of the method and multiply by the proper dilu­ trated HNO3 to the beaker. Cover with a tion factors. watchglass, return to the hotplate, and gently reflux the solution. 8. Report 6.6 Continue heating, adding more acid as Report sodium, total-recoverable (00929), con­ necessary until the digestion is complete (in­ centrations as follows: less than 10 mg/L, one dicated by a light-colored residue). Evaporate decimal; 10 mg/L and above, two significant just to dryness. figures. 6.7 Add 6 mL 6Af HC1 solution per 100 mL original sample and warm the solution to dissolve the residue. 9. Precision 6.8 Filter (Whatman No. 41 or equivalent) It is estimated that the percent relative stand­ the sample and wash the watchglass and beaker ard deviation for total recoverable sodium is with demineralized water. Rinse the filter with greater than 13 percent at 2.76 mg/L and hot 0.3M HC1. Dilute to the original volume greater than 5 percent at 96.9 mg/L. with demineralized water. 6.9 While aspirating the blank use the automatic zero control to set the digital display References to read zero concentration. While aspirating standards use the automatic concentration con­ Fishman, M. J., and Downs, S.C., 1966, Methods for analysis trol to set the digital display to read concentra­ of selected metals in water by atomic absorption: U.S. tion of standards. Use at least six standards. Geological Survey Water-Supply Paper 1540-C, p. 38-41. Calibrate the instrument each time a set of U.S. Environmental Protection Agency, 1979, Methods for samples is analyzed and check calibration at chemical analysis of water and wastes: Cincinnati, reasonable intervals. p. 273.1-1. Sodium, atomic emission spectrometric, ICP

Parameter and Code: Sodium, dissolved, 1-1472-85 (mg/L as Na): 00930

2. Summary of method method utilizing an induction-coupled argon Sodium is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 429

Sodium, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Sodium, total, 1-5473-85 (mg/Kg as Na): none assigned Sodium, total, 1-5474-85 (mg/kg as Na): none assigned

2. Summary of method spectrometry. See method 1-5473, metals, ma­ 2.1 A sediment sample is dried, ground, jor, total-in-sediment, atomic absorption spec­ and homogenized. The sample is then treated trometric, direct. and analyzed by one of the following 2.1.2 The sample is digested with a combina­ techniques. tion of nitric, hydrofluoric, and perchloric acids 2.1.1 The sample is fused with a mixture of in a Teflon beaker heated on a hotplate at lithium metaborate and lithium tetraborate in 200 °C. Sodium is determined on the resulting a graphite crucible in a muffle furnace at solution by atomic absorption spectrometry. 1,000°C. The resulting bead is dissolved in See method 1-5474, metals, major and minor, acidified, boiling, demineralized water, and total-in-sediment, atomic absorption spec­ sodium is determined by atomic absorption trometric, direct. 431

Sodium adsorption ratio, calculation

Parameter and Code: Sodium adsorption ratio, 1-1738-85: 00931

1. Application 7. Calculations me/L Na This method may be applied to any sample SAR = for which measured values for sodium, calcium, me/L Ca + me/L Mg and magnesium are available. 8. Report Report sodium adsorption ratio, calculation 2. Summary of method (00931), as follows: less than 1.0, one decimal; The sodium adsorption ratio (SAR) is com­ 1.0 and above, whole numbers. puted from the individual determination of 9. Precision sodium, calcium, and magnesium after con­ Precision data are not available for this version of each to milliequivalents per liter method, but reproducibility should be com­ (me/L). parable to that of the individual determinations.

433

Sodium, percent, calculation

Parameter and Code: Sodium, percent, 1-1740-85: 00932

| 1. Application 7. Calculations This method may be applied to any sample Sodium (percent) for which measured values for sodium, me/L Na X100 potassium, calcium, and magnesium are 2 me/L (Na + K + Ca + Mg) available. 8. Report Report sodium, percent, calculation (00932), as whole numbers. 2. Si ry of method 9. Precision Percent sodium is computed from the milli- Precision data are not available for this equivalent per liter (me/L) of sodium, potassium, method, but reproducibility should be com­ calcium, and magnesium. parable to that of the individual determinations. 435

Solids, residue on evaporation at 180°C, dissolved, gravimetric

Parameter and Code: Solids, residue on evaporation at 180°C, dissolved 1-1750-85 (mg/L): 70300

1. Application residue is heated at 180 °C, but this temperature The residue-on-evaporation method is ap­ is insufficient to dehydrate calcium sulfate com­ plicable to all water regardless of concentration, pletely. Residues of water with a high nitrate provided that the residue layer in the evapora­ content may lose as much as 30 mg/L on tion dish is kept sufficiently thin. heating. 2.4 Because many of the salts in the residue 2. Summary of method are hygroscopic, an efficient desiccant must be 2.1 A volume of filtered sample that will used. Silica gel (indicating), anhydrous yield less than 200 mg residue is evaporated Mg(ClO4)2 or CaSO4, and Mg(ClO4)2-3H2O are just to dryness on a steam bath. The residue is satisfactory and recommended. CaCl2 is not then dried at 180°C for exactly 2 hours, cooled suitable. Under no circumstances should the in a desiccator, and immediately weighed. dried residues be allowed to stand for long 2.2 The weight of the residue is limited to periods of time before weighing. 200 mg to ensure subjection of all the residue to the full effects of drying at 180 °C. Volumi­ 3. Interferences nous residues will often seal over during the There are no known interferences to this evaporation process and entrap pockets of method. water that will not be completely vaporized dur­ ing the drying process. Massive residues also 4. Apparatus release their water of crystallization more slow­ 4.1 Desiccator, charged with indicating ly than do thin films of residue. The chemical silica gel or other efficient desiccant. composition of the sample has a marked effect 4.2 Oven, 180°C, uniform temperature on the dissolved-solids value obtained, but the throughout. percentage of error incurred for any given 4.3 Platinum evaporating dishes, 75- to chemical type of water is independent of the 125-mL capacity, weighing less than 50 g, or zir­ total concentration if the residue film is kept conium dishes. Platinum or zirconium are thin. recommended for precise work because the 2.3 Biocarbonate is converted to carbonate change in weight of glass or porcelain dishes in the evaporation and drying process. The may introduce appreciable error into the deter­ following general observations have been mination. reported by Howard (1933). The residues of 4.4 Steam bath. carbonate-type water that contain considerable magnesium chloride can be expected to lose 5. Reagents some weight (as much as 50 or 100 mg/L) dur­ None required. ing the drying process; however, such loss of weight is usually more than offset by the water 6. Procedure of crystallization tightly held by the salts. Most 6.1 Pipet a volume of filtered sample con­ of the water of crystallization is driven off from taining 10 to 200 mg dissolved solids (500 mL sulfates of sodium and magnesium when the max) into a tared platinum dish.

437 438 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6.2 Evaporate the sample just to dryness on a steam bath. 6.3 Dry in an oven at 180 °C for 2.0 h. where 6.4 Cool in a desiccator and immediately ST = overall precision, milligrams per liter, weigh. Record the weight to the nearest 0.1 mg. and X = concentration of dissolved solids, milli­ 7. Calculations grams per liter. The correlation coefficient is 0.7633. Dissolved solids (mg/L) = 9.2 Precision for dissolved solids for six of the 22 samples expressed in terms of the per­ 1,000 X mg residue cent relative standard deviation is as follows: mL sample Number of Mean Relative standard deviation laboratories (mp/L) _____(percent)_____ 27 59.2 8 8. Report 28 267 4 Report solids, residue on evaporation at 39 524 11 180 °C, dissolved (70300), concentrations as 28 558 2 29 1160 4 follows: less than 1,000 mg/L, whole numbers; 49 1760 3 1,000 mg/L and above, three significant figures. Reference 9. Precision 9.1 Precision for dissolved solids for 22 Howard, C. S., 1933, Determination of total dissolved solids samples within the range of 60 to 1760 mg/L in water analysis: Industrial Engineering Chemistry, may be expressed as follows: Analytical Edition, v. 5. p. 4. Solids, residue on evaporation at 105°C, dissolved, gravimetric

Parameter and Code: Solids, residue at 105°C, dissolved, 1-1749-85 (mg/L): 00515

1. Application 4. Apparatus The residue-on-evaporation method is ap­ 4.1 Desiccator, charged with indicating plicable to all water regardless of concentration, silica gel or other efficient desiccant. provided that the residue layer in the 4.2 Oven, 105 °C, uniform temperature evaporating dish is kept sufficiently thin. throughout] 4.3 Platinum evaporating dishes, 75- to 2. Summary of method 125-mL capacity, weighing less than 50 g, or 2.1 A volume of filtered sample that will zirconium dishes. Platinum or zirconium is yield less than 200 mg residue is evaporated recommended for precise work because the just to dryness on a steam bath. The residue is change in weight of glass or porcelain dishes dried at 105 °C for 2.0 h, cooled in a desiccator, may introduce appreciable error into the deter­ and immediately weighed. mination. 2.2 The weight of the residue is limited to 4.4 Steam bath. 200 mg to ensure subjection of all the residue to the full effects of drying at 105°C. Volumi­ 5. Reagents nous residues will often seal over during the None required. evaporation process and entrap pockets of water that will not be completely vaporized dur­ 6. Procedure ing the drying process. Massive residues also 6.1 Pipet a volume of filtered sample con­ release their water of crystallization more slow­ taining 10 to 200 mg dissolved solids (500 mL ly than do thin films of residue. The chemical max) into a tared platinum dish. composition of the sample has a marked effect 6.2 Evaporate the sample just to dryness on on the dissolved-solids value obtained, but the a steam bath. percentage of error incurred for any given 6.3 Dry in an oven at 105 °C for 2.0 h. chemical type of water is independent of the 6.4 Cool in a desiccator and immediately total concentration if the residue film is kept weigh. Record the weight to the nearest 0.1 mg. thin. 2.3 Because many of the salts in the residue 7. Calculations are hygroscopic, an efficient desiccant must be used. Silica gel (indicating), anyhydrous Dissolved solids (mg/L) Mg(ClO4)2 or CaSO4, and Mg(ClO4)2-3H2O are 1,000 satisfactory and recommended. CaCl2 is not X mg residue suitable. Under no circumstances should the sample dried residues be allowed to stand for long periods of time before weighing. 8. Report Report solids, residue on evaporation at 3. Interferences 105 °C, dissolved (00515), concentrations as There are no known interferences to this follows: less than 1,000 mg/L, whole numbers; method. 1,000 mg/L and above, three significant figures. 439 440 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 9. Precision Reference It is estimated that the percent relative stand­ ard deviation of this method is greater than 8 American Public Health Association and others, 1980, percent at 59 mg/L and greater than 3 percent Standard methods for the examination of water and at 1760 mg/L. wastewater [15th ed]: Washington, D.C., p. 92-4. Solids, residue on evaporation at 105°C, total, gravimetric

Parameter and Code: Solids, residue on evaporation at 105°C, total, I-3750-85 (mg/L): 00500

1. Application 4. Apparatus 1.1 This method may be used to determine the 4.1 Desiccator, charged with indicating total-solids concentration of any natural or silica gel or other efficient desiccant. treated water or industrial waste. 4.2 Oven, 105 °C, uniform temperature 1.2 Total residue represents the sum of both throughout. dissolved and suspended (including colloidal) 4.3 Platinum evaporating dishes, 75- to material in a sample. The determination is not 125-mL capacity, weighing less than 50 g, or exact, because of the compromise that must be zirconium dishes. Platinum or zirconium is made in selecting the temperature at which the recommended because the change in weight of evaporated residue is to be dried. At tempera­ glass or porcelain dishes may introduce ap­ tures sufficient to release water of hydration of preciable error into the determination. the hydrated salts that form on evaporation, there is risk of volatilization of the more volatile 6. Procedure dissolved or suspended materials in the sample. 6.1 Shake the sample vigorously and rapidly On the other hand, drying at a sufficiently low pipet a suitable aliquot of unfiltered sample. temperature to conserve volatiles fails to re­ 6.2 Transfer the sample to a tared platinum move much of the entrapped water and ordinary evaporating dish. water of hydration. Because of these factors, the 6.3 Rinse the pipet with demineralized water determination must be considered as providing to ensure transfer of all particulate matter to only an approximation of the sum of dissolved the evaporating dish. and suspended matter. 6.4 Evaporate the sample just to dryness on 1.3 The determination is not very useful; a steam bath. determination of dissolved solids (method 6.5 Dry in an oven at 105 °C for 2.0 h. 1-1749) and suspended solids (method 1-3765) 6.6 Cool in a desiccator and immediately provides more useful information. weigh. Record the weight to the nearest 0.1 mg. 2. Summary of method A volume of well-mixed sample is evaporated 7. Calculations to dryness. The residue is dried at 105 °C for 2.0 h, cooled in a desiccator, and immediately 1,000 weighed. Total solids (mg/L) = X mg residue mL sample 3. Interferences Care must be taken to ensure that a repre­ sentative sample is provided. Usually, large, 8. Report floating particles are excluded from the Report solids, residue on evaporation at sample. 105 °C, total (00500), concentrations as follows:

441 442 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS less than 1,000 mg/L, whole numbers; 1,000 percent at 59 mg/L and greater than 3 percent mg/L and above, three significant figures. at 1760 mg/L.

Reference 9. Precision U.S. Environmental Protection Agency, 1979, Methods for It is estimated that the percent relative stand­ chemical analysis of water and wastes: Cincinnati, ard deviation of this method is greater than 8 p. 160.3. Solids, residue at 105°C, suspended, gravimetric i Parameter and Code: j Solids, residue at 105°C, suspended, I-3765-85 (mg/L): 00530

1. Application 6.2 Quantitatively collect the suspended This method may be used to determine the material from the sample on a tared glass-fiber suspended-solids concentration of any natural filter disk. A blank should be determined with or treated water or industrial waste. each set of samples. 6.3 Wash the suspended material on the 2. Summary of method filter sparingly with demineralized water. 2.1 Suspended solids are those that are re­ 6.4 Dry the residue and filter disk overnight tained on a glass-fiber filter. The determined at 105 °C. value is fairly representative of the sample but 6.5 Cool in a desiccator and weigh the filter does not accurately represent the suspended- disk containing the dry residue to the nearest sediment concentration of a stream; suspended- 0.1 mg. Record the weight. solids values should not be confused with sedi­ ment concentration, which is the more accurate 7. Calculations measure of material in suspension. 7.1 Apply a correction for any loss shown by 2.2 The unfiltered sample is mixed thor­ the blank. oughly and an appropriate volume is rapidly 7.2 Determine suspended solids in milli­ poured into a graduated cylinder. The sus­ grams per liter as follows: pended solids are collected on a glass-fiber filter, and the insoluble residue is dried and Suspended solids, mg/L = weighed. 1000 X mg residue 3. Interferences sample Precipitation hi the sample during storage, such as iron, will produce erroneously high 8. Report results. Report solids, residue at 105 °C, suspended (00530), concentrations as follows: less than 4. Apparatus 1,000 mg/L, whole numbers; 1,000 mg/L and 4.1 Desiccator, charged with indicating above, three significant figures. silica gel or other efficient desiccant. 4.2 Filtration apparatus, consisting of suc­ 9. Precision tion flask, gooch crucible, glass-fiber filter disk, Precision data are not available for this and suitable holder. method. 4.3 Oven, 105 °C, uniform temperature throughout. Reference 6. Procedure Guy, H. P.» 1969, Laboratory theory and methods for sedi­ 6.1 Shake the sample bottle vigorously and ment analysis: Techniques of Water-Resources Inves­ rapidly pour a suitable volume into a graduated tigations of the U.S. Geological Survey, book 5, chapter cylinder. Record the volume. Cl, 58 p.!

443

Solids, volatile-on-ignition, dissolved, gravimetric

Parameter and Code: Solids, volatile-on-ignition, dissolved, 1-1753-85 (mg/L): 00520

1. Application 5. Reagents This method may be used to analyze any None required. natural, treated, or industrial water and other wastewater. 6. Procedure 6.1 Determine dissolved solids as directed in 2. Summary of method method 1-1750. The residue obtained after determination of 6.2 Place the weighed evaporating dish in a dissolved solids (method 1-1750) is ignited at muffle furnace at 550 °C; heat for 1 h. 550 °C. The loss in weight of residue represents 6.3 Remove and cool in a desiccator; weigh a measure of dissolved volatile solids. and record the weight to the nearest 0.1 mg.

3. Interferences 7. Calculations 3.1 None of the substances commonly occur­ Solids, volatile on ignition, dissolved, mg/L = ring in natural waters interfere with this method. 1000 3.2 Because of the great variability in the X (ER-IR) nature of the compounds that can be present in mL sample the sample, particularly in samples of industrial and other wastes, the determination can be con­ where sidered only an approximation of the amount ER ~ weight of dissolved solids, milligrams, of volatile material present. Some of the volatile IR = weight of ignited residue, milligrams. material may have been released during the determination of dissolved solids. Moreover, ig­ 8. Report nition at 550 °C volatilizes water of hydration Report solids, volatile-on-ignition, dissolved from the hydrated salts present. (00520), concentrations as follows: less than 1,000 mg/L, whole numbers; 1,000 mg/L and 4. Apparatus above, three significant figures. 4.1 Muffle furnace, 550 °C. 4.2 For additional items of required ap­ 9. Precision paratus, see solids, dissolved (method 1-1750). Precision data are not available for this method

445

Solids, volatile-on-ignition, total, gravimetric

Parameter and Code: i Solids, volatile-on-ignition, total, 1-3753-85 (mg/L): 00505

1. Application 5. Reagents This method may be used to analyze any None required. natural, treated, or industrial water and other waste. 6. Procedure 6.1 Determine the total solids as directed in 2. Summary of method solids, total (method 1-3750). A measured volume of well-mixed, unfiltered 6.2 Place the weighed evaporating dish in a sample is evaporated to dryness. The residue is muffle furnace at 550 °C; heat for 1 h. dried at 105 °C for 2.0 h, cooled in a desiccator, 6.3 Remove and cool in a desiccator. Weigh and immediately weighed. See solids, total and record the weight to the nearest 0.1 mg. (method 1-3750). The residue is then ignited at 550 °C and weighed, the difference in weight 7. Calculations representing total volatile solids. Solids, volatile-on-ignition, total mg/L = 3. Interferences 3.1 Care must be taken to ensure that a 1000 representative sample is provided. Usually, X (ER-IR) large, floating particles are excluded from the inL sample sample. 3.2 Because of the great variability in the where nature of the compounds that can be present in ER = weight of evaporated total residue, the sample, particularly in samples of industrial milligrams, and other wastes, the determination can be con­ IR = weight of ignited total residue, milli- sidered only an approximation of the amount grams. of volatile material present. Much of the volatile material may have been released during the 8. Report determination of total residue. Moreover, igni­ Report solids, volatile-on-ignition, total tion at 550 °C certainly volatilizes water of (00505), concentrations as follows: less than hydration from the hydrated salts present. 1,000 mg/L, whole numbers; 1,000 mg/L and above, three significant figures. 4. Apparatus 4.1 Muffle furnace, 550 °C. 9. Precision 4.2 For additional items of required ap­ Precision data are not available for this paratus, see solids, dissolved (method 1-3750). method.

447

Solids, volatile-on-ignition, suspended, gravimetric

Parameter and Code: Solids, volatile-on-ignition, suspended, 1-3767-85 (mg/L): 00535

1. Application 6. Procedure This method may be used to analyze any 6.1 Determine suspended solids as directed natural or treated water or industrial waste. in method 1-3765. 6.2 Place the weighed gooch crucible con­ 2. Summary of method taining the dry suspended solids in a muffle fur­ The dry residue obtained for the determina­ nace at 550 °C; heat for 1 h. A blank should be tion of suspended solids (method 1-3765) is determined with each set of samples. ignited at 550 °C for 1 h. The loss on ignition 6.3 Remove and cool hi a desiccator. Weigh corresponds to the amount of volatile sus­ and record the weight to the nearest 0.1 mg. pended solids. 7. Calculations 3. Interferences 3.1 None of the substances commonly occur­ Solids, volatile-on-ignition, suspended, mg/L = ring in natural waters interfere with this method. 1000 3.2 Because of the great variability in the X (ER-IR) nature of the compounds that can be present in mL sample the sample, particularly in samples of industrial waste, the determination can be considered on­ where ly an approximation of the amount of volatile ER = weight of dry suspended solids, material present. Some of the volatile material milligrams, may have been released during the determina­ IR = weight of ignited suspended solids, tion of suspended solids. Moreover, ignition at milligrams. 550 °C certainly volatilizes water of hydration from the hydrated salts present. 8. Report Report solids, volatile-on-ignition, suspended 4. Apparatus (00535), concentrations as follows: less than 4.1 Muffle furnace, 550 °C. 1,000 mg/L, whole numbers; 1,000 mg/L and 4.2 For additional items of required ap­ above, three significant figures. paratus, see solids, suspended (method 1-3765). 9. Precision 5. Reagents Precision data are not available for this None required. method.

449

Solids, volatile-on-ignition, total-in-bottom-material, gravimetric i Parameter and Code: Solids, volatile-on-ignition, total-in-bottom-material, dry wt, 1-5753-85 (mg/kg): 00496

1. Application bottom of a platinum evaporating dish. Place This method may be used to analyze samples in an oven at 105 °C and heat overnight. of bottom material. Usually, only the material 6.2 Place the dish containing the dry sam­ that will pass a 2-nun sieve is taken for analysis. ple in a desiccator, cool, and weigh to the nearest 0.1 mg. 2. Summary of method 6.3 Ignite the weighed dry residue at 550 °C A portion of well-mixed sample is dried at for 1 h, cool in a desiccator, and weigh to the 105 °C. A portion of dry, well-mixed sample is nearest 0.1 mg. carefully weighed and then ignited at 550 °C. The loss of weight on ignition represents the 7. Calculations amount of volatile solids in the sample. Solids, volatile-on-ignition (mg/kg) = 3* Interferences None. (DR-IR) X 106 4. Apparatus DR 4.1 Desiccator, charged with indicating silica gel or other efficient desiccant. where 4.2 Muffle furnace, 550 °C. 4.3 Oven, 105°C, uniform temperature IR = weight of ignited residue, milligrams, throughout. and 4.4 Platinum evaporating dishes, 75- to DR = weight of dry residue, milligrams. 125-mL capacity, weighing less than 50 g. Platinum is recommended because the change 8. Report in weight of glass or porcelain dishes may in­ Report solids, volatile-on-ignition, total-in- troduce appreciable error into the deter­ bottom-material (00496), concentrations as mination. follows: less than 1,000 mg/kg, whole numbers; 1,000 mg/kg and above, three significant 5. Reagents figures. None required. i 9. Precision 6. Procedure Precision data are not available for this 6.1 Spread approx 1 g of sample in the method. 451

Solids, nonvolatile-on-ignition, dissolved, calculation

Parameter and Code: Solids, nonvolatile-on-ignition, dissolved, 1-1752-85 (mg/L): 00525

1. Application where This method may be used to calculate non­ DS = dissolved solids, milligrams per liter, volatile dissolved solids on any sample for which and the dissolved solids (method 1-1750) and the volatile dissolved solids (method 1-1753) have DV = solids, volatile on ignition, dissolved, been determined. milligrams per liter.

2. Summary of method 8. Report The nonvolatile solids are determined by sub­ Report solids, nonvolatile-on-ignition, dis­ tracting the volatile dissolved solids (method solved (00525), concentrations as follows: less 1-1753) from the dissolved solids (method than 1,000 mg/L, whole numbers; 1,000 mg/L 1-1750). and above, three significant figures.

7. Calculations 9. Precision Solids, nonvolatile-on-ignition, Precision data are not available for this dissolved, mg/L = DS-DV method.

453

Solids, nonvolatile-on-ignition, total, calculation

Parameter and Code: Solids, nonvolatile-on-ignition, total, 1-3752-85 (mg/L): 00510

1* Application where This method may be used to calculate total TS = total solids, milligrams per liter, nonvolatile solids on any sample for which the and total solids (method 1-3750) and the total TV = solids, volatile on ignition, total, milli­ volatile solids (method 1*3753) have been grams per liter. determined. 8. Report 2. Summary of method Report solids, nonvolatile-on-ignition, total Total nonvolatile solids are determined by (00510), concentrations as follows: less than subtracting the total volatile solids (method ltOOO mg/L, whole numbers; 1,000 mg/L and 1-3753) from the total solids (method 1-3750). above, three significant figures.

7. Calculations 9. Precision Solids, nonvolatile-on-ignition, Precision; data are not available for this total, (mg/L) TS-TV method. ! 455

Solids, nonvolatile-on-ignition, suspended, calculation

Parameter and Code: Solids, nonvolatile-on-ignition, suspended, 1-3766-85 (mg/L): 00540

1. Application where This method may be used to calculate non­ SS = suspended solids, milligrams per liter, volatile suspended solids on any sample for and which the suspended solids (method 1-3765) and VS = solids, volatile on ignition, suspended, volatile suspended solids (method 1-3767) have milligrams per liter. been determined. 2. Summary of method 8. Report The nonvolatile suspended solids are deter­ Report solids, nonvolatile-on-ignition, sus­ mined by subtracting the volatile suspended pended (00540), concentrations as follows: less solids (method 1-3767) from the suspended than 1,000 mg/L, whole numbers; 1,000 mg/L solids (method 1-3765). and above, three significant figures.

7. Calculations 9. Precision Solids, nonvolatile on ignition, Precision data are not available for this suspended, mg/L = SS-VS method.

457

Solids, sum of constituents, calculation

Parameter and Code: Solids, dissolved, 1-1751-85 (mg/L): 70301

1. Application assumption that all material present hi the The calculation method is applicable only to theoretical anhydrous residue be in the same those analyses that include determinations of form as reported hi the analysis, with the ex­ all major constituents. Such analyses are con­ ception of bicarbonate. sidered to be complete for all practical purposes. All bicarbonate in solution is assumed to exist The chemist can never be certain of the com­ as carbonate in the residue: pleteness of the analysis, but for most alkaline waters other than brines, the determination of silica, calcium, magnesium, sodium, potassium, 2HCO31- CO§2 + CO2 + H2O alkalinity, sulfate, chloride, and nitrate is suf­ ficient. The wide range of metals possible in acid water precludes assumptions as to the com­ Therefore, the bicarbonate in solution is pleteness of the analysis. mathematically converted to its equivalent weight as carbonate in the residue. 2. Summary of method 2.3 The accuracy of the result is dependent 2.1 The concentrations of all determined on the completeness of the analysis and on the constituents are converted mathematically in­ validity of each reported constituent concen­ to the forms in which they would normally exist tration. in an anhydrous residue. These quantities are then added. If the water is grossly polluted, it 7. Calculations is usually necessary to determine the nitrogen 7.1.1 If a field bicarbonate determination was components. Concentration of carbonaceous made, convert bicarbonate concentration to car­ material can be estimated by redissolving the bonate concentration as follows: residue on evaporation and successively treating it with several amounts of hydrogen peroxide. The difference in weight between the nonoxidized residue and the oxidized residue is 3 an indication of the carbonaceous solids. The 2.03 estimated carbonaceous solids are not included in the calculated dissolved solids, but are one 7.1.2 Alternatively, convert alkalinity concen­ measure of the differences to be expected be* tration reported as mg/L CaCO3 to carbonate tween dissolved solids determined by residue on concentration: evaporation and by calculation (Howard, 1933). 2.2 The conversion of the constituents in the analysis to the forms in which they would nor* mg/L COg2 = mg/L CaCO3 X 0.60 mally exist in an anhydrous residue involves many unknown variables. Consequently, sum­ 7.2 Add all determined dissolved consti­ marizing the constituents requires the arbitrary tuents reported in the analytical statement. The

459 460 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS following constituents must be included: cal­ 9. Precision cium, magnesium, sodium, potassium, alkalini- Precision data are not available for this ty, chloride, nitrate, sulfate, and silica. method, but reproducibility should be com­ parable to that of the individual determinations. 8. Report Report solids, dissolved, calculated (70301), Reference concentrations as follows: less than 100 mg/L, Howard, C. S., 1933, Determination of total dissolved solids whole numbers; 100 mg/L and above, two in water analysis: Industrial Engineering Chemistry, significant figures. Analytical Edition, v. 5t p. 4. Specific conductance, electrometric, Wheatstone bridge

Parameters and Codes: ! Specific conductance, lab, 1-1780-85 (jiS/cm at 25°C): 90095 Specific conductance, lab, automated, 1-2781-85 (pS/cm at 25°C): 90095

1. Application is unnecessary because a factor called the cell This method may be applied to all natural, constant (C) can be determined. The cell con­ treated, and industrial water. stant is determined experimentally with a standard solution of known conductance. A 2. Summary of method 0.00702AT potassium chloride solution has a 2.1 Specific conductance is determined by specific conductance of 0.001000 S/cm at 25 °C. using a Wheatstone bridge in which a variable The relation between resistance (fl), cell con­ resistance is adjusted so that it is equal to the stant (O, and specific conductance tK) is shown resistance of the unknown solution between in the following equation, where K is known and platinized electrodes of a standardized conduc­ R is determined: tivity cell. The ability of a solution to conduct an electric current is a function of the concen­ RK = C tration and charge of the ions in the solution and also depends on the rate at which the ions Thus, if the resistance of the cell, when filled can move under the influence of an electrical with 0.00702AT KC1, is, for example, 350 ohms, potential. As the number of ions per unit the cell constant would be 0.35 for the conduc­ volume of solution increases, the rate at which tivity cell used. If the conductivity cell having individual ions can move decreases, because of a cell constant of 0.35 is filled with a sample at interionic attraction and other effects. For this 25 °C and the observed resistance is 865 ohms, reason, a graph of total-ion concentration ver­ the specific conductance of the sample could be sus specific conductance, even for solutions of derived from the cell-constant equation: a single salt, is a simple straight line only for rather dilute solutions. As specific conductance increases beyond about 5,000 ftS/cm at 25 °C, the regression line curves, and beyond 50,000 /iS/cm, the specific conductance is generally an unsatisfactory index of solute-ion concen­ Substituting values from the example yields the tration. following: 2.2 The temperature of the electrolyte af­ fects the ionic velocities and, consequently, the 0.35 conductance. Conductance increases about 2 = 0.00405 Sat25°C percent per degree Celsius, which is about the 865 same as the temperature coefficient of viscosi­ ty of water. 2.4 Unless a constant-temperature room or 2.3 In the determination of the specific con­ bath is available, adjustment of sample temper­ ductance, preparing a cell having electrodes ex­ ature (T) to exactly 25 °C is difficult. For most actly 1 cm2 in area and exactly 1 cm apart work, specific conductance is computed from would be difficult. Moreover, such an exact cell the following equation: /iS/cm = (R of 0.00702AT 461 462 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

KC1 at T of sample measurement X 1,000) X Specific conductance Cell constant (\IR of the sample). (pS/cm at 25 *C) (cm-1) 2.5 New conductivity cells should be visual­ 20-1,000 0.2 ly checked for cleanliness and platinum uni­ 40-2,000 .5 100-4,000 1.0 formity before use. Subsequently, they should 200-10,000 2.0 be cleaned and replatinized whenever the read­ 400-20,000 5.0 ings become erratic or indistinct or inspection 1,000-40,000 10.0 shows that any platinum black has flaked off. One platinization will usually suffice for a period 4.2 Conductivity meter, Wheatstone-bridge of several months. To platinize the electrodes, type or equivalent direct-reading meter. clean them in chromic acid solution and rinse 4.3 Thermometer, 0 to 50 °C, graduated in thoroughly in several changes of water. Place 0.1 °C. Some direct-reading conductivity meters the electrodes in a solution of chloroplatinic acid have automatic temperature compensation built and lead acetate (dissolve 3 g HgPtC^ in 10 mL into the meter. Alternatively, a thermistor water to which 20 mg Pb(C2H3O2)2 is added; device as described by Hughes (1966) provides commercial platinizing solutions are also a convenient means of directly computing the available). Connect the electrodes to two dry necessary temperature correction. cells (IVi-V each) in parallel and reverse the direction of the current once per minute for 6 5. Reagent min, or until the shiny platinum surface is Potassium chloride solution, 0.00702JV: covered. Avoid deposition of amorphous Dissolve 0.5234 g KC1, dried at 180 °C for 1 h, platinum on the electrodes. in demineralized water and dilute to 1,000 mL. Repeat the electrolytic process, using 10-percent sulfuric acid to remove chlorine. 6. Procedure 6.1 Meters measuring resistance: The When not in use, the cell should be kept im­ manufacturer's instructions for operation of the mersed in distilled water. bridge should be followed explicitly. A constant- 2.6 The accuracy and reproducibility of temperature room or 25 °C bath simplifies results obtainable depend largely on the type temperature consideration. Where such facili­ of bridge used, but can approach 2 percent with ties are not available, the sample should be this equipment. Close attention to temperature brought to approximately room temperature is essential for reliable work. before the determination. However, samples in 2.7 Additional information on the theory the laboratory are seldom at exactly the same and practice of specific conductance measure­ temperature because of the influence of drafts, ments can be found in Daniels and Alberty sunlight, radiators, ovens, and open flames. The (1966), and in Scofield (1932). temperature of each sample should be deter­ 2.8 This procedure may be automated by mined at the time of measurement. the addition of commercially available instru­ 6.1.1 Prepare a graph of resistance of mentation. 0.00702j?V KC1 throughout the operating- temperature range. 3. Interferences 6.1.2 Rinse the cell with sample. None. 6.1.3 Measure the resistance of the sample and record the temperature at the time of 4. Apparatus measurement. Record temperature to the 4.1 Conductivity cell: Cells of at least two nearest 0.1 °C. different cell constants should be available to 6.1.4 Determine the resistance of 0.00702W measure a wide range of conductivities. The KC1 at the temperature at which the sample table below provides a general guide to the resistance was measured from the graph selection of an appropriate cell constant. prepared in step 6.1.1. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 463 6.2 Direct-reading meters with built-in samples within the range of 9.0 to 2080 /tS/cm temperature compensators: can be expressed as follows: 6.2.1 Prepare a table of conductance of 0.00702JST KC1 throughout the operating- ST = 0.054X -3.80 temperature range. Calculate and enter in table the correction factors where measured con­ where ductance deviates from correct conductance. ST = overall precision, microsiemens per cen­ 6.2.2 Immerse probe-type cell in sample. (Cell timeter, at 25 °C, will have been immersed in deionized water and and blotted dry with tissue just before use.) X — specific conductance, microsiemens per 6.2.3 Measure conductance and temperature, centimeter, at 25 °C. and record both measurements. The correlation coefficient is 0.9005. 6.2.4 Refer to table prepared in 6.2.1 and ap­ 9.2 Precision for specific conductance for ply appropriate correction factors to con­ five of the 36 samples expressed in terms of the ductance measurements as necessary. percent relative standard deviation is as follows:

Number of Mean Relative standard deviation 7. Calculations laboratories ____(percent)_____ Specific conductance (pS/cm at 25 °C) 32 9.0 19 31 112 4 28 557 3 R of 0.00702AT KC1 36 1170 5 X 1,000 55 2080 47 R of sample 9.3 Using automated instrumentation, anal­ where ysis of two test samples by a single laboratory R = resistance in ohms. for 25 replicates of each resulted in mean values NOTE 1. Further calculations are unnecessary of 96.9 and 1,664 /*S/cm and standard deviations when measurements are made with a direct- of 0.8 and 11 jiS/cm, respectively. reading meter with builtin temperature com­ pensator. References

8. Report Daniels, Farrington, and Alberty, R. A., 1966, Physical Report specific conductance, /*S/cm at 25 °C chemistry! (3rd ed.): New York, John Wiley and Sons, (90095), as follows: less than 1,000 /iS/cm, whole 671 p. numbers; 1,000 jtS/cm and above, three signifi­ Hughes, L. S., 1966, Use of thermistor-thermometer in deter­ cant figures. mination of specific conductance: U.S. Geological Survey Water-Supply Paper 1822, p. 66. Scofield, C. S., 1932, Measuring the salinity of irrigation 9. Precision waters and of soil solutions with the Wheatstone bridge: 9.1 Precision for specific conductance for 36 U.S. Department of Agriculture Circular 232.

Strontium, atomic absorption spectrometric, direct

Parameters and Codes: Strontium, dissolved, 1-1800-85 (pg/L as Sr): 01080 Strontium, total recoverable, I-3800-85 (pg/L as Sr): 01082 Strontium, suspended recoverable, I-7800-85 0*9/1- as Sr): 01081 Strontium, recoverable-from-bottom-material, dry wt, I-5800-85 fog/g as Sr): 01083

1. Application 3. Interferences 1.1 This method may be used to analyze 3.1 Sodium and potassium decrease the water, brines, and water-suspended sediment strontium ionization in the flame. To control the containing from 10 to 5000 jig/L of strontium. ionization, 1,000 mg/L of potassium are added Samples containing more than 5,000 jig/L need to both standards and samples. to be diluted. 3.2 Aluminum, phosphate, and silica inter­ 1.2 Suspended recoverable strontium is fere but are masked by the addition of calculated by subtracting dissolved strontium lanthanum. from total recoverable strontium. 3.3 Nitrate interferes, but in the presence of 1.3 This method may be used to analyze bot­ lanthanum chloride-potassium chloride solution tom material containing at least 1.0 jig/g of at least 2,000 mg/L can be tolerated. The addi­ strontium. If the sample solution contains more tion of nitric acid in the field to preserve sam­ than 5,000 jig/L of strontium, it must be diluted. ples causes no problem. 1.4 Total recoverable strontium in water- 3.4 Low strontium values result even in the suspended sediment needs to undergo presence of potassium and lanthanum if the preliminary digestion-solubilization by method dissolved-splids concentration exceeds 2,500 1-3485, and recoverable strontium from bottom mg/L. For this reason, brines and highly material needs to undergo preliminary diges­ mineralized waters must either be diluted or tion-solubilization by method 1-5485 before be­ analyzed by the standard-addition method. For ing determined. the standard-addition method, the dissolved 1.5 Samples containing more than 2,500 solids content of the samples must be reduced mg/L of total solutes need first to be diluted. to less than 20,000 mg/L. If the strontium concentration in the diluted sample is below detection, the undiluted sam­ 4. Apparatus ple needs to be analyzed by the standard- 4.1 Atomic absorption spectrometer addition method. equipped with electronic digital readout and automatic zero and concentration controls. 2. Summary of method 4.2 Refer to the manufacturer's manual to 2.1 Strontium is determined by atomic ab­ optimize instrument for the following: sorption spectrometry. Lanthanum chloride and Grating ———————— Visible excess potassium chloride are added to mask Wavelength ————— 460.7 nm interferences and control ionization of stron­ Source (hollow-cathode tium in the flame (Fishman and Downs, 1966). lamp) ———————— Strontium 2.2 This procedure may be automated by the Oxidant ———————— Air addition of a sampler, a proportioning pump, Fuel —————————— Acetylene and a strip-chart recorder or a printer or both Type of flame ———— Slightly (fig. 44). ; reducing 465 466 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

pirator Water Long O.OSlin mixing coil 2.52 mL/min 1050501 ' O.OSlin Sample t ^ * \ 2.52 mL/min Air , O 3- O.OSlin Sampler I L> 2.52 mL/min PS- 3 Lanthanum 0.035in chloride ste 0.42 mL/min To sampler' 4 < O.OSlin Water wash rece ptacle 2.52 mL/min

Figure 44.—Strontium manifold

4.3 The 100-mm (4-in.), single-slot burner the instrument each time a set of samples is allows a working range of 10 to 5,000 /*g/L. Dif­ analyzed and check calibration at reasonable ferent burners may be used according to intervals. manufacturers' instructions. 7. Calculations 5. Reagents 7.1 Determine the micrograms per liter of 5.1 Lanthanum chloride-potassium chloride dissolved or total recoverable strontium in each solution: Dissolve 117.3 g La2O3 ^ a minimum sample from the digital display or printer while amount of dilute HC1. Add 19.1 g KC1, and aspirating each sample. Dilute those samples dilute to 1,000 mL with demineralized water. containing strontium concentrations that ex­ 5.2 Strontium standard solution, 1.00 mL = ceed the working range of the method and 100 fig Sr: Dissolve 0.1684 g SrCO3 in a mini­ multiply by the proper dilution factors. mum amount of dilute HC1, and dilute to 1,000 7.2 To determine micrograms per liter of mL. suspended recoverable strontium, subtract 5.3 Strontium working standards: Prepare dissolved-strontium concentration from total- a blank and a series of at least six working recoverable-strontium concentration. standards containing from 10 to 5,000 jig/L of 7.3 To determine micrograms per gram of Sr by appropriate dilutions of strontium stand­ strontium in bottom-material samples, first ard solution. Add 1.0 mL of LaCl3-KCl solution determine the micrograms per liter of strontium to each 10 mL of working standards prepared. as in paragraph 7.1; then For example, to 500 mL of a working standard, add 50 mL LaCl3-KCl solution. of original digest /*g/L Sr X 6. Procedure Sr (pg/g) = 1,000____ 6.1 Add 1.0 mL LaCl3-KCl solution to 10.0 wt of sample (g) mL of sample solution. 6.2 Aspirate the blank (10 mL demineralized water plus 1.0 mL LaCl3-KCl solution) to set 8. Report the automatic zero control. Use the automatic 8.1 Report strontium, dissolved (01080), concentration control to set concentrations of total-recoverable (01082), and suspended- standards. Use at least six standards. Calibrate recoverable (01081), concentrations as follows: METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 467 less than 100 j*g/L> nearest 10 /xg/L; 100 jig/L the percent relative standard deviation is as and above, two significant figures. follows: 8.2 Report strontium, recoverable-from- Number of Mean Relative standard deviation bottom-material (01083), concentrations as laboratories G*g/L) (percent) follows: less than 10 /xg/g, nearest microgram 8 55.0 22 per gram; 10 figlg and above, two significant 12 99.2 30 figures. 12 583 32 10 592 14 19 818 12 9. Precision 13 1260 24 9.1 Precision for dissolved strontium for 39 10 2150 25 samples within the range of 55 to 2790 9 2790 5 may be expressed as follows: 9.3 It is estimated that the percent relative standard deviation for total recoverable and 12.886 suspended recoverable strontium and for recov­ erable strontium in bottom material will be where greater than that reported for dissolved ST = overall precision, micrograms per liter, strontium. and X — concentration strontium, micrograms Reference per liter. Fishman, M. J., and Downs, S. C., 1966, Methods for The correlation coefficient is 0.7322. analysis of selected metals in water by atomic absorp­ 9.2 Precision for dissolved strontium for tion: U.S. Geological Survey Water-Supply Paper eight of the 39 samples expressed in terms of 1540-C, p. 41-3.

Strontium, atomic emission spectrometric, ICP

Parameter and Code: Strontium, dissolved, 1-1472-85 (pg/L as Sr): 01080

2. Summary of method method utilizing an induction-coupled argon Strontium is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP.

469

Strontium, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Strontium, total, 1-5474-85 (mg/kg as Sr): none assigned

2. Summary of method hotplate at 200°C. Strontium is determined on A sediment sample is dried, ground, and the resulting solution by atomic absorption homogenized. The sample is digested with a spectrometry. See method 1-5474, metals, ma­ combination of nitric, hydrofluoric, and per­ jor and minor, total-in-sediment, atomic absorp­ chloric acids in a Teflon beaker heated on a tion spectrometric, direct. 471

Sulfate, dissolved, colorimetric, complexometric, methylthymol blue, automated-segmented flow

Parameter and Code: Sulfate, dissolved, 1-2822-85 (mg/L as 804): 00945

1. Application Absorption cell ——— 15 mm This method can be used to determine concen­ Wavelength ————— 460 nm trations of sulfate in surface, domestic, and in­ Cam —————————— 30/h (6/1) dustrial water in the range from 5 to 100 mg/L. The range can be extended to 300 mg/L by 5. Reagents decreasing the sample-to-water ratio. Samples 5.1 Barium chloride stock solution, 1.301 containing higher concentrations need to be g/L: Dissolve 1.526 g BaCl2-2H2O (assay 99.0 diluted. percent min) in demineralized water and dilute to 1,000 mL. 2. Summary of method 5.2 EDTA solution: Dissolve 6.75 g NH4C1 The sample stream is passed through a and 40 g disodium ethylenediaminetetra-acetic cation-exchange column before an acid solution acid (EDTA) in 500 mL demineralized water and is added containing equimolar quantities of 57 mL concentrated NH4OH (sp gr 0.90). Dilute barium chloride and methylthymol blue (MTB). to 1 L with demineralized water. Any sulfate ion is thereby precipitated as 5.3 Hydrochloric acid, lAf: Add 83 mL con­ barium sulfate. When the mixture is then made centrated hydrochloric acid (sp gr 1.19) to de- basic, the remaining barium ions form a com­ mineralized water and dilute to 1 L. plex with MTB, and the absorbance of the un- 5.4 Methylthymol blue (MTB) solution, complexed MTB, which is gray, is directly 0.5417 g/100 mL: Dissolve 0.5417 g MTB proportional to the amount of sulfate original­ (Eastman Kodak No. 8068, M.W. = 866.73) in ly present (Lazarus and others, 1968). demineralized water and dilute to 100 mL. 5.5 MTB-barium chloride reagent: The puri­ 3. Interferences ty of MTB may vary from one lot to another; Color is the only significant interference. In­ this variation affects the linearity of the terfering cations are removed by a cation- analytical curve (Colovos and others, 1976). It exchange column, which is incorporated into the is, therefore, necessary to adjust the Ba-MTB system. ratio by the following calibration procedure in order to achieve a linear relationship between 4. Apparatus absorbance and sulfate concentration. Add 25.0 4.1 Technicon AutoAnalyzer II, consisting mL BaCl2 stock solution to each of several of a sampler, cartridge manifold, proportioning 500-mL volumetric flasks. Then add volumes of pump, colorimeter, voltage stabilizer, recorder, MTB solution ranging from 26.0 to 36.0 mL and printer. (0.96 to 0.69 Ba-MTB molar ratio), in 2.0-mL in­ 4.2 With this equipment the following crements, to each flask. Add 4.0 mL 1M HC1 operating conditions have been found satisfac­ and an appropriate volume of demineralized tory for the ranges from 5 to 100 mg/L and from water to bring the total volume to 100 mL. 100 to 300 mg/L: Dilute to 500 mL with 95-percent ethanol and

473 474 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS add 1 mL Brij-35 solution. Analyze eight sulfate MTB. Use this ratio when preparing subse­ standards covering the 5- to 100-mg/L operating quent solutions of MTB-barium chloride range (5.0,10.0, 20.0, 30.0, 40.0, 50.0, 75.0, and reagent. Repeat this calibration procedure only 100.0 mg/L) with reagent solutions of varying when a different lot of MTB is used. Ba-MTB molar ratios. Do not vary the in­ 5.6 Sodium hydroxide, 0.18M: Cautiously strumental parameters, but adjust the baseline dissolve 7.2 g NaOH in demineralized water and as necessary. Plot an analytical curve of peak dilute to 1 L. height versus known sulfate concentration for 5.7 Sulfate standard solution /, 1.00 mL = each Ba-MTB ratio. Determine least-squares 1.00 mg SO4: Dissolve 1.4787 g Na2SO4, dried equation and a coefficient of correlation on a for 2 h at 180°C, in demineralized water and programmable calculator or computer. From dilute to 1,000 mL. the coefficient of correlation, determine the op­ 5.8 Sulfate working standards: Prepare a timum Ba-MTB ratio for a particular lot of blank and 1,000 mL each of a series of sulfate

0.030 in Air 0.32 mL/min 5-turn coil To waste(l) (7990) 0.065 in Water 1.60 mL/min Ion-exchange column 0.030 in Sample 116-6006-01 0.32 mL/min or Dowex 50W-X8 20-50 Mesh 0.051 in Waste (1) 1.00 mL/min Sampler 4 30/h 0.030 in Air 6/lcam 20-turn coil 22-turn coil 0.32 mL/min ** 0.045 in Methylthymol blue 0.70 mL/min

0.035 in Sodium hydroxide Colorimeter 0.42 mL/min 460 nm To sampler 4 Water 15- mm cel 0.073 in wash 2.00 mL/min receptacle ** 0.065 in Waste (2) 1.60 mL/min Recorder Proportioning pump

0.034in polyethylene ** Silicone rubber Figure 45.—Sulfate, methylthymol blue manifold, low range, 5 to 100 mg/L SO4 - * METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 475 working standards by appropriate quantitative 6. Procedure dilution of sulfate standard solution I as follows: 6.1 Set up manifold (fig. 45 or 46, NOTE! 1 and 2). Sulfate standard solution 1 Sulfate concentration (mL) (mo/L) NOTE 1. The manifold includes a cation exchange column consisting of a 2.0-mm II 0.0 0.0 5.0 5.0 Pyrex tube approx 19-cm (7.5-in.) long filler 10.0 10.0 with Dowex 50W-X8 (20 to 50 mesh), o 20.0 20 30.0 30 equivalent, cation-exchange resin. The resin i 40.0 40 held in place by a loose plug of glass wool 01 50.0 50 75.0 75 the exit end. Regenerate the resin daily with 1A 100.0 100 HC1. Tygon transmission tubing may be use* 150.0 150 200.0 200 in place of the Pyrex tube. The column must b 300.0 300 replaced if air bubbles are introduced.

0.030 in Air 0.32 mL/min 5-turn coil To Waste(l) 0.073 in Water *> 2.00 mL/min Ion-exchange column 0.015 in Sample f ^\ 116-6006*01 0.10 mL/min or Dowex SOW-X8 Waste(l) ' ^^"^ * 20-50 Mesh 0.051 in ———————— Sampler 4 * 1.00 mL/min 30/h 0.030 in Air ft/team 20- turn coil 22- turn coil « —————— (Hfffft frjnm| 0.32 mL/min * k '• 0.045 in Methylthymol blue** 0.70 mL/min 0.035 in Sodium hydroxide Colorimeter 0.42 mL/min To sampler 4 0.073 in Water ——I wash "*" 2.00 mL/min T receptacle — "ir 0.073 in Waste (2)** 2.00 mL/min Recorder Proportioning pump

0.034 in polyethylene ** Silicone rubber Figure 46.—Sulfate, methylthymol blue manifold, high range, 100 to 300 mg/L SO4 476 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS NOTE 2. At the end of each day wash the tions as follows: 5-9 mg/L, nearest 1 mg/L; 10 system with a solution of EDTA: Place the mg/L and above, two significant figures. MTB line and the NaOH line in water for a few minutes and then into the EDTA solution for 9. Precision 10 min. Wash the system with water for 15 min 9.1 Precision for dissolved sulfate for 16 before shutting down. samples within the range of 14 to 943 mg/L may 6.2 Allow colorimeter and recorder to warm be expressed as follows: for at least 30 min. 6.3 Adjust the baseline to read zero scale ST = 0.029X + 3.42 divisions on the recorder with all reagents, but with demineralized water in the sample line. where 6.4 Place a complete set of standards and a ST = overall precision, milligrams per liter, blank in the first positions of the first sample and tray, beginning with the most concentrated X = concentration of sulfate, milligrams per standard. Place individual standards of differ­ liter. ing concentrations in approx every eighth posi­ The correlation coefficient is 0.8863. tion of the remainder of this and subsequent 9.2 Precision for dissolved sulfate for five of sample trays. Fill remainder of each sample tray the 16 samples expressed in terms of the per­ with unknown samples. cent relative standard deviation is as follows: 6.5 Begin analysis. When the peak from the most concentrated working standard appears on Number of Mean Relative standard deviation the recorder, adjust the STD CAL control until laboratories (mp/L) _____(percent)_____ the flat portion of the curve reads full scale 7 13.9 12 10 59.2 9 12 143 5 7. Calculations 6 526 2 7.1 Prepare an analytical curve by plotting 15 943 3 the height of each standard peak versus its respective sulfate concentration. References 7.2 Compute the sulfate concentration in milligrams per liter of each sample by compar­ Colovos, G., Panesar, M. R., and Parry, E. P., 1976, Lineariz­ ing its peak height to the analytical curve. Any ing the calibration curve in determination of sulfate by baseline drift that may occur must be taken into the methylthymol blue method: Analytical Chemistry, account when computing the height of a sam­ v. 48, p. 1693-6. ple or standard peak. Lazarus, A., Lorange, E., and Lodge, J. P., Jr., 1968, New automated microanalyses for total inorganic fixed nitrogen and for sulfate ion in water, in Trace inorganics 8. Report in water American Chemical Society, Advances in Report sulfate, dissolved (00945), concentra­ Chemistry Series, No. 73, p. 164-71. Sulfate, turbidimetric, barium sulfate, automated-discrete

Parameter and Code: Sulfate, dissolved, 1-2823-85 (mg/L as SCty: 00945

1. Application Reaction tem­ This method may be used to determine con­ perature - ambient centrations of sulfate in surface, domestic, and Sample industrial water in the ranges of 0.2 to 1000 volumes 0.450 mL with 0.050 mL of mg/L. Samples containing greater concen­ diluent for 0.2 to 10.0 trations must first be diluted. Three work­ mg/L ing ranges are provided: from 0.2 to 10.0 mg/L, 0.200 mL with 0.050 mL of from 10 to 200 mg/L, and from 200 to 1000 diluent for 10 to 200 mg/L. mg/L 0.140 mL with 0.075 mL of 2. Summary of method diluent for 200*1000 Sulfate ion is reacted with barium chloride mg/L (NOTE 1) under acidic conditions to form barium sulfate. Reagent The absorbance of the resulting suspension is volumes 0.25 mL BaCl2-NaCi-HCl- measured photometrically and is proportional gelatin solution and 0.25 to the sulfate concentration present in the mL sulfate standard solu­ original sample (Santiago and others, 1975). tion IV for 0.2 to 10 mg/L 3. Interferences 1.0 mL BaCl2-NaCl-HCl- Suspended matter in large amounts will in­ gelatin solution for 10 to terfere. Natural color exceeding 50 platinum 200 mg/L cobalt units may interfere. Silica, at concentra­ 2.0 mL BaCl2-NaCl-HCl- tions less than 200 mg/L, does not interfere. gelatin solution for 200 to 1000 mg/L (NOTE 1) 4. Apparatus NOTE 1. Sample-to-diluent ratio and reagent 4.1 Discrete analyzer system, American volumes must be optimized for each individual Monitor IQAS or equivalent. instrument according to manufacturer's 4.2 With this equipment the following specifications. operating conditions have been found satisfac­ tory for the ranges: from 0.2 to 10.0 mg/L, from 5. Reagents 10 to 200 mg/L, and from 200 to 1000 mg/L. 5.1 Barium chloride-sodium chloride- Wavelength 340 nm for 0.2 to 10.0 mg/L hydrochloric acid-gelatin solution. 410 nm for 10 to 200 mg/L 5.1.1. Sulfate ranges 0.2 to 10.0 mg/L and 10 458 nm for 200 to 1000 to 200 mg/L: Dissolve 20 g BaCl2-2H2O in 500 mg/L mL demineralized water, and add 10 mL con­ Absorption centrated HC1 (sp gr 1.19), 0.5 g gelatin (USP) cell ——— 1 cm square, temperature- and 20 g NaCL Mix well, dilute to 1,000 mL with controlled, flow-through demineralized water, and filter. Prepare fresh quartz cuvette weekly.

477 478 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.1.2. Sulfate range, 200 to 1000 mg/L: the high range use 200,300,500,800, and 1,000 Dissolve 10 g BaCl2-2H2O in 500 mL deminer- mg/L. Place samples and quality-control alized water, and add 10 mL concentrated HC1 reference samples in the remainder of the sam­ (sp gr 1.19), 0.125 g gelatin (U8P) and 20 g Nad. ple turntable. Mix well, dilute to 1,000 mL with demineralized 6.3 Begin analysis (NOTE 2). water, and filter. Prepare fresh weekly. NOTE 2. The cathode-ray tube (CRT) will 5.2 Sulfate standard solution I, 1.00 mL = acknowledge parameter and concentration 10.0 mg SO4: Dissolve 14.787 g Na2SO4, dried range selected, listing each sample-cup number for 2 h at 180°C, in demineralized water and and corresponding concentrations calculated dilute to 1,000 mL. from the working curve. During each run, the 5.3 Sulfate standard solution //, 1.00 mL = CRT display will provide a plot of standards, 1.00 mg SO4: Dilute 100 mL standard solution samples, and list blank and slope calculations. I to 1,000 mL with demineralized water. Retain copy of all information obtained from the 5.4 Sulfate standard solution III, 1.00 mL = printer. 0.100 mg SO4: Dilute 100 mL standard solution II to 1,000 mL with demineralized water. 7. Calculations 5.5 Sulfate standard solution IV, 1.00 mL = Determine the milligrams per liter of sulfate 0.010 mg SO4: Dilute 10.0 mL sulfate standard in each sample from either the CRT display or solution II to 1,000 mL with demineralized the computer printout. water. 5.6 Sulfate working standards: Prepare a 8. Report blank and 1,000 mL each of a series of sulfate Report sulfate, dissolved (00945), concentra­ working standards by the appropriate dilution tions as follows: 0.2 to 10.0 mg/L, one decimal, of sulfate standard solution I, II, or III as 10 mg/L and above, two significant figures. follows: 9. Precision Standard Standard Standard Sulfate Precision expressed in terms of the standard solution 1 solution H solution III concentration (mL) (mL) (mL) . (mg/L) deviation the and percent relative standard 5.0 0.5 deviation for replicates analysis by a single 10.0 1.0 operator is as follows (NOTE 3): 50.0 5,0 100.0 10.0 20.0 20 50.0 50 Relative 125.0 125 standard 20.0 * 200 Mean Number of Standard deviation deviation (mg/L) replicates (mg/L) (percent) 30.0 300 50.0 ' 500 0.7 22 0.08 11.0 80.0 800 1.3 22 .14 7.6 100.0 1000 2.7 22 .14 5.0 4.4 22 .12 2.7 6.2 22 .12 1.9 14.3 21 .11 .5 6. Procedure 272 22 1.14 4.2 6.1 Set up analyzer and computer-card 112 21 .68 3.2 387 10 5.5 1.4 assignments according to the manufacturer's 612 10 5.0 .8 instructions. 6.2 Place standards, beginning with the low­ est concentration, in ascending order (computer- NOTE 3. Some imprecision has been observed calibration curve) in the first five positions on in the range from 8 to 12 mg/L. More precise the sample turntable. For the low range use 0.0, data can be obtained by diluting samples within 0.5, 1.0, 5.0, and 10.0 mg/L SO4; for the mid- this range and determining sulfate in the 0.2 to range use 10, 20,50,125, and 200 mg/L; and for 10 mg/L range. Sulfate, ion-exchange chromatographic, automated

Parameters and Codes: Sulfate, dissolved, 1-2057-85 (mg/L as SO^: 00945 Sulfate, dissolved, 1-2058-85 (mg/L as SOj: 00945

2. Summary of method anions in their acid form are measured using an Sulfate is determined sequentially with six electrical-conductivity cell. See method 1-2057, other anions by ion-exchange chromatography. anions, ion-exchange chromatographic, auto­ Ions are separated based on their affinity for mated and method 1-2058, anions, ion-exchange the exchange sites of the resin. The separated chromatographic, precipitation, automated. 479

Sulfate, titrimetric, thorin

Parameter and Code: ! Sulfate, dissolved, 1-1820-85 (mg/L as 804): 00945

1. Application 4. Apparatus This method may used to analyze water con­ 4.1 Absorption cells, 50-mm. The cement in taining from 0.5 to 200 mg/L of sulfate. Samples some cells reacts with thorin to produce a red with greater concentrations need to be diluted color. Cells should be tested for thorin reaction, or analyzed by an alternate method. and those that produce a red color in 10 to 15 min should be rejected. Alternatively, 100-mL 2. Summary of method beakers may be used, providing the titration 2.1 Thorin and barium react to form a com­ assembly is designed to accept such beakers. plex that is deep red. The intensity of the color 4.2 Buret, 10-mL. is dependent on pH, indicator concentration, 4.3 Cation-exchange column (fig. 47). The and nature of the solvent. The color is more in­ column should be filled to within 5 to 8 cm of tense in organic than in aqueous solutions and the top with Amberlite IR-120 or equivalent, also varies in intensity with different organic solvents. The color reaction can be utilized to titrate sulfate directly with barium chloride by adding a large volume of organic solvent to the sample and titrating in this mixed medium. When the end point is detected spectrometrical- ly, the preferred titration medium is 80-percent alcohol maintained at pH 5 with a sodium acetate buffer. 2.2 The end point may also be detected by ——- Pyrex-glass tubing %-in ID viewing the solution through a didymium glass filter. When visual detection is made, the titra­ tion medium should be 66-percent dioxane, ad­ justed to a pH between 2.2 and 5. The initial yellow color of thorin in the dioxane-water medium changes to pink at the end point. - Resin

3. Interferences Thorin reacts with many metals, including calcium; therefore, all metal ions must be re­ moved by cation exchange prior to titration. — Pyrex-glass-wool plug.or fritted-glass disk Phosphate interferes somewhat by coprecipita- tion; with 100 mg/L of sulfate, 10 and 20 mg/L of phosphate result in a positive error of about C : >i— Screw-clamp to regulate flow 2 and 3 percent, respectively. Color may inter­ fere with the spectrometric reading and require Rubber tubing correction. Figure 47.—Cation-exchange column for sulfate

481 482 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS operating on the hydrogen cycle. The resin is (10.0 mL max) into a 50-mm absorption cell and regenerated with 30-percent (volume-to-volume) adjust the volume to 10.0 mL. HC1 solution. The frequency of regeneration 6.4 Add 40 mL solvent indicator solution. depends on the mineral content of the samples. 6.5 Insert cell in titration assembly and The need for regeneration may be determined begin analysis. by checking a small portion of column effluent 6.6 Titrate with BaCl2 (1.00 mL o 0.20 mg for the presence of calcium. SOf). 4.4 Spectrophotometer with titration 6.7 Determine a blank correction by assembly for use at 520 nm. Commercial in­ titrating demineralized water. The blank is con­ strumentation is available. Follow manufac­ stant throughout the concentration range of the turer's instruction for optimizing instrument method. A blank of 0.05 mL has been found. conditions. Correct for water color when necessary.

5. Reagents 7. Calculations 5.1 Barium standard solution, 1.00 mL o 1,000 0.20 mg SOf: Dissolve 0.5086 g BaCl2-2H20 SO4 in mg/L = (assay 99.0 percent minimum) in demineralized mL sample water and dilute to 1,000 mL. The exact concen­ tration of this standard solution may be verified 0.2 X (mL titrant-mL blank) by titrating a known volume of sulfate stand­ ard sblution as in the analytical procedure. 8. Report 5.2 Solvent indicator solution: Dissolve Report sulfate, dissolved (00945), concentra­ 0.025 g thorin and 0.5 g anhydrous sodium tions as follows: less than 10 mg/L9 one decimal; acetate in 10 mL water, warming gently if 10 mg/L and above, two significant figures. necessary to ensure complete dissolution. Filter the solution through Whatman No. 1 filter 9. Precision paper into 1L of 95-percent ethanol and discard 9.1 Precision for dissolved sulfate for 11 the filter paper without washing or rinsing. Add samples within the range of 9.8 to 394 mg/L 12 mL glacial CH3COOH (sp gr 1.06) and mix. may be expressed as follows: Difficulty in preparing a dear solution of the in­ dicator is probably due to poor-quality thorin ST = 0.026X + 0.686 reagent. 5.3 Sulfate standard solution, 1.00 mL — where 1.00 mg SOj2: Dissolve 1.4787 g N^SO* dried ST = overall precision, milligrams per liter, for 2 h at 180 °C, in demineralized water and and dilute to 1,000 mL. X = concentration of sulfate, milligrams per liter. 6. Procedure The correlation coefficient is 0.9010. 6.1 Rinse the cation-exchange columns with 9.2 Precision for dissolved sulfate for four 20 to 30 mL of sample and discard the rinse. of the 11 samples expressed in terms of the per­ cent relative standard deviation is as follows: (Check a portion for the presence of calcium.) 6*2 Pass sufficient sample through the ex­ Number of Mean Relative standard deviation changer to provide at least 10 mL of effluent laboratories (mg/L) ____(percent)____ for the determination. 13 9.8 6 18 50.8 4 6.3 Pipet a volume of sample containing less 18 141 2 than 2 mg SOj2 and 10 mg dissolved solids 16 394 3 Sulfide, titrimetric, iodometric

Parameter and Code: Sulfide, total, 1-3840-85 (mg/L as S): 00745

1. Application thiosulfate required for the blank and the 1.1 This method may be used to analyze water volume used for the sample. and water-suspended sediment containing more 2.3 This method is similar to that in an arti­ than 0.5 mg/L of sulfide. cle published by the American Public Health 1.2 Water-suspended sediment may be Association (1980). analyzed by this method if sample is shaken vigorously and a suitable aliquot of well-mixed 3. Interferences sample is rapidly withdrawn. Reducing substances such as suljites and 1.3 Water containing dissolved sulfides heavy-metal ions react with iodine, which con­ readily loses hydrogen sulfide, particularly if the tributes to positive errors. Oxygen and other ox- pH of the sample is low. Oxygen destroys idants may react with hydriodic acid to liberate sulfides by oxidation, particularly if the pH of iodine, which contributes to negative: errors. the sample is high. Aeration and agitation of the sample should, therefore, be avoided. The addi­ 4. Apparatus tion of 2 g of zinc acetate per liter of water will 4.1 Buret, 10-mL capacity. fix the sample for several days. Acidic water 4.2 Flasks, Erlenmeyer, 250-mL capacity. must be neutralized before addition of zinc acetate. 5. Reagents 5.1 Hydrochloric acid, concentrated (sp gr 2. Summary of method 1.19). i 2.1 This iodometric method does not dif­ 5.2 Iodine standard solution, O.OKW: ferentiate the forms of the sulfide ion in Dissolve 6 g iodate-free KI in appro:* 25 mL solution. water. Add 1.2690 g resublimed I2. When solu­ 2.2 Sulfide is reacted with an excess of tion is complete, dilute to 1L. Standardize with iodine in acid solution, and the remaining iodine O.OKW Na2S2O3, using starch as an indicator. is then determined by titration with sodium thiosulfate, using starch as an indicator (Kolthoff and others, 1969). 0.010 XmL Normality of I2 = mLI2 H+1 -2 + I2 —* S + 2I'1 Adjust the normality of the iodine standard solution, if necessary, to 0.010 by addition of small quantities of demineralized water or I2 + 2S2Og2 iodine as indicated by the first titration. Con­ firm the normality by ^standardization. A blank is treated exactly the same as the 5.3 Potassium iodide, crystals, iodate-free: samples. The sulfide concentration is calculated The KI can be tested for lOjj1 by dissolving from the difference between the volume of about 0.1 g in 5 mL water, acidifying mth 1 or

483 484 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 2 drops concentrated H2SO4 (sp gr 1.84) and 6. Procedure adding 2 to 3 mL starch indicator solution. Im­ 6.1 Shake the sample vigorously and im­ mediate appearance of blue color indicates the mediately pipet a volume of sample with ZnS presence of lO^1; slow color formation is caus­ in suspension containing less than 1.5 mg S~2 ed by atmospheric oxidation. (100.0 mL max) into a 250-mL Erlenmeyer flask, 5.4 Sodium thiosulfate standard solution, and adjust the volume to approx 100 mL. 0.010N: Dissolve 2.482 g Na2S2O3'5H2O in car­ 6.2 Prepare a blank of approx 100 mL de- bon dioxide-free water and dilute 1 L with car­ mineralized water, and carry it through the pro­ bon dioxide-free water. Standardize against cedure with the sample. KIO3 as follows: Dry approx 0.5 g KIO3 for 2 6.3 Add 10.0 mL O.OKW I2 and mix. h at 180 °C. Dissolve 0.3567 g in water and 6.4 Without delay add 10 mL concentrated dilute to 1,000 mL. Pipet 25.0 mL KIO3 solu­ HCL tion into a 250-mL Erlenmeyer flask, then add 6.5 Immediately titrate the excess I2 with successively 75 mL deionized water and 0.5 g O.OKW Na2S2O3, adding 2 to 3 mL starch in­ iodate-free KI. After solution is complete, add dicator solution as the end point is approached 10 mL HC1 (sp gr 1.19). Allow the stoppered (light-straw color). flask to stand 5 min in the dark and titrate with Na2S2O3 solution, adding starch indicator solu­ 7. Calculations tion as the end point is approached (light-straw 1,000 color): S-2 (mg/L) = X 0.1603 mT. sample 0.25 X (mL blank titrant-mL sample titrant) Normality of Na2S2O3 = mL Na2S2O3 8. Report Report sulfide, total (00745), concentrations as follows: 0.5 to 10 mg/L, one decimal; 10 mg/L Adjust the normality of the thiosulfate stand­ and above, two significant figures. ard solution, if necessary, to 0.010 by addition of small quantities of demineralized water or 9. Precision sodium thiosulfate as indicated by the first Precision data are not available for this titration. Confirm the normality by restand- method. ardization. 5.5 Starch indicator solution, stable (NOTE References 1). NOTE 1. A convenient substitute for starch in­ American Public Health Association, 1980, Standard methods for the examination of water and wastewater dicator solution is the product thyodene, sold (15th ed.): Washington, D.C., p. 448. by Fisher Scientific Co. It can be used in its dry Kolthoff, I. M.( Sandell, E. B., Meehan, E. J., and Brucken- form and produces an end point similar to that stein, S., 1969, Quantitative Chemical Analysis (4th ed): of starch. New York, Macmillan, p. 857. Thallium, atomic absorption spectrometric, graphite furnace

Parameter and Code: Thallium, dissolved, 1-1866-85 (/*g/L as Tl): 01057

1. Application at 276.8 nm, equipped with deuterium This method may be used to analyze water background correction, graphite furnace, and containing at least 1 ptg/L of thallium. Samples recorder with 2.5-mv or 5.0-mv range. containing more than 9 /xg/L need either to be 4.2 Refer to the manufacturer's manual to diluted or a smaller volume needs to be used for optimize instrumental performance. analysis. 4.3 Graphite furnace, capable of reaching temperatures sufficient to atomize thallium. 2. Summary of method CAUTION: Dial settings frequently sire inac­ 2.1 Thallium is determined by atomic ab­ curate and newly conditioned furnaces require sorption spectrometry in conjunction with a temperature calibration. Use the following graphite furnace and the method of standard operating conditions: additions. The sample is placed in the graphite Drying temperature ———— 100 °C tube and is then evaporated to dryness, charred, Charring temperature ——— 400 °C and atomized. The absorbance signal generated Atomizing temperature — 2400 °C during atomization is recorded. Known concen­ Drying time ———————— (NOTE 1) trations of thallium are added to aliquots of the Charring time ——————— 15 s sample in the tube and the technique is re­ Atomizing time —————— 10 s peated. The absorbances are then plotted and Purge gas —————————— Argon, 25 the concentration of thallium is determined by cnrVmin extrapolation. normal 2.2 Pretreatment of the graphite tube with flow ammonium molybdate and addition of ammo­ NOTE 1. Set drying time for as many seconds nium nitrate to the sample in the graphite tube as the total microliters of sample plus standard are employed to reduce background scattering. injected. 2.3 For discussion of standard additions, see 4.4 Graphite tubes, compatible with furnace. this chapter, Analytical techniques, atomic ab­ Standard graphite tubes are preferred. sorption spectrometry. 4.5 Pipets, microliter with disposable tips, 1- to 50-/*L capacity. 3. Interferences 4.6 Thallium light source, thallium False peaks or recorder deflections below the electrodeless-discharge lamp. baseline often occur during the atomization 4.7 Argon, standard, welder's grade, com­ cycle because of heavy background scattering mercially available. Nitrogen may also be used in this wavelength region (276.8 nm) and if recommended by the instrument because of the requirement for very close align­ manufacturer. ment of the deuterium background corrector and source (electrodeless-discharge lamp). 5. Reagents 5.1 Ammonium hydroxide solution, 3M: 4. Apparatus Dilute 20 mL concentrated NH4OH (sp gr 0.90) 4.1 Atomic absorption spectrometer, for use to 100 mL with demineralized water.

485 486 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.2 Ammonium molybdate solution, 8.7 g/50 will give a signal less than 40 percent of full mL: Dissolve 9.2 g (NH4)6Mo7O24'4H2O in 40 scale on the recorder. mL 3M ammonium hydroxide solution and 6.5 Choose a volume of thallium working dilute to 50 mL with demineralized water. standards that, when added to the sample ali­ 5.3 Ammonium nitrate solution, 25 g/50 mL: quot, will produce a 50-, 100-, and 150-percent Dissolve 25 g NH4NO3 in 50 mL demineralized increase in signal peak height (NOTE 3). Inject water. the same volume of demineralized water to the 5.4 Nitric acid, concentrated (sp gr 1.41): sample for the blank spike. High-purity, Ultrex or equivalent. NOTE 3. To determine the approx signal (ab- 5.5 Nitric acid solution, (1 + 499): Mix 1 sorbances or peak heights) of the thallium work­ part concentrated HNO3 (sp gr 1.41) with 499 ing standards, inject 30 /xL of the low working parts demineralized water. standard, cycle, and record signal. From this in­ 5.6 Thallium standard solution I, 1.00 formation, the volume of standard can be mL = 1000 jig TL Dissolve 1.303 g T1NO3 in de- determined. mineralized water. Add 2 mL concentrated 6.6 Inject in the graphite tube the aliquot of HNO3 (sp gr 1.41) and dilute to 1000 mL with sample and blank as determined in steps 6.4 and demineralized water. 6.5. Cycle as given in paragraph 4.3 and record 5.7 Thallium standard solution II, 1.00 absorbance or peak height. Repeat process with mL = 20.0 fig Tl: Dilute 20.0 mL thallium sample and the standard additions of thallium standard solution I to 1,000 mL with nitric acid working standards as determined in steps 6.4 solution (1 + 499). and 6.5. Analyze the sample plus standards 5.8 Thallium working standards: Dilute 50, twice (NOTE 4). 100, and 150 jiL each of thallium standard solu­ NOTE 4. If background interferences occur as mentioned in paragraph 2.2, inject 20 j*L am­ tion II to 250 mL with nitric acid solution. These working standards represent concentra­ monium nitrate solution to each sample, stand­ ard, and blank. tions of 4, 8, and 12 pg//*L of thallium. Prepare fresh daily (NOTE 2). 7. Calculations NOTE 2. Clean the 250-mL volumetric flasks 7.1 Plot absorbances (or peak heights) of with dilute nitric acid (1 + 50) and rinse with sample plus standards on the vertical axis of a demineralized water immediately before use. graph and the mass, in pg, added on the horizon­ Rinse the 50-jiL micropipet disposable plastic tal axis. tip twice in a solution of nitric acid (1 + 2), twice 7.2 Fit the points to a straight line by the in demineralized water, and twice in thallium least-squares method and extrapolate the line standard solution II before preparing the work­ to the horizontal axis. The mass of thallium ing standards. present in the sample is the reading at the horizontal intercept. 6. Procedure 7.3 Determine the micrograms per liter of 6.1 Prior to use, rinse pipet tips twice with dissolved thallium in each sample as follows: a solution of nitric acid (1 + 2) and then twice in demineralized water. 6.2 Pretreat the graphite tube. Inject 25 pL mass Tl in sample (pg) ammonium molybdate solution and cycle as volume of sample (^L) follows: dry for 20 s at 110°C, char for 15 s at 550 °C, and atomize for 10 s at 2500 °C. Use an 8. Report argon flow of 12 mL/min in the interrupt mode. Report thallium, dissolved (01057), concentra­ Repeat injection and cycle three times. tions to the nearest microgram per liter. 6.3 Inject 30 /*L of sample into the graphite tube and dry, char, and atomize as given in step 9. Precision 4.3. 9.1 Precision for dissolved thallium for four 6.4 From the signal's peak height obtained samples expressed in terms of the percent in paragraph 6.3, choose a sample volume which relative standard deviation is as follows: METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 487

Number of Relative standard deviation laboratories _____(percent)____ 9.2 Analyses of two samples sis: times each by a single operator resulted in mean 4 3.2 75 values of 5.6 and 10.9 /*g/L and relative stand­ 5 3.4 38 6 3.8 39 ard deviations of 10 and 3 percent, respec­ 3 5.0 20 tively.

Tin, atomic absorption spectrometric, hydride, automated

Parameters and Codes: Tin, dissolved, 1-2851-85 (/*g/L as Sn): 01100 Tin, total recoverable, 1-4851-85 (Aig/L as Sn): 01102 Tin, suspended recoverable, 1-7851-85 (jig/L as Sn): 01101 Tin, recoverabie-from-bottom-materiai, dry wt, 1-6851-85 fog/g as Sn): 01103

1. Application barium, beryllium, cadmium, chromium, cobalt, 1.1 This method may be used to analyze water lead, lithium, manganese, mercury, molybdenum, and water-suspended sediment containing from nickel, selenium, and zinc at concentrations to 1 1 to 10 jig/L of tin. Samples containing more mg/L each, or from calcium, potassium, and so­ than 10 /Ag/L need to be diluted. dium at concentrations up to 1,000 mg/L each. 1.2 Suspended recoverable tin is calculated 3.2 Antimony, arsenic, copper, and silver by subtracting dissolved tin from total concentrations greater than 200 jig/L, 100 jig/U recoverable tin. 300 /ig/L and 100 jig/L, respectively, depress the 1.3 This method may used to analyze bot­ tin absorption. At 300 jig/L of antimony, 200 tom material containing at least 0.1 /ig/g of in­ Mg/L of arsenic, 400 jig/L of copper, and 200 /ig/L organic tin. Sample solutions containing more of silver, the depression is approx 16,15,8, and than 10 /ig/L must be diluted. 20 percent, respectively. 1.4 Total recoverable tin in water-suspended 3.3 Magnesium at concentrations greater sediment needs to undergo preliminary than 300 mg/L depresses the tin absorption. At digestion-solubilization by method 1-3485, and 400 and 1,000 mg/L, the depression is approx­ recoverable tin from bottom material needs to imately 20 and 24 percent, respectively. undergo preliminary digestion-solubilization by method 1-5485 before being determined. 4. Apparatus 4.1 Atomic absorption spectrometer and 2. Summary of method recorder. 2.1 Tin is reduced to tin hydride with sodi­ Refer to the manufacturer's manual to op­ um borohydride. Interferences from most ma­ timize instrument for the following: jor and trace elements in the hydride-generation Grating ———————— Ultraviolet step are reduced to insignificance by addition Wavelength counter — 286.3 ma of EDTA. The tin hydride is stripped from the Source (electrodeless- solution by a stream of nitrogen gas and con­ discharge lamp) ——— Tin veyed to a tube furnace placed in the optical 4.2 Autotransformer, variable: Superior path of an atomic absorption spectrometer, Powerstat Type 3 PN 1010 or equivalent. where it is decomposed to atomic tin. The op­ 4.3 Pyrometer, portable, 0 to 1200 °C. Ther- tical absorbance is measured and related to the molyne Model PM-20700 or equivalent. tin concentration in the original sample. 4.4 Stripping-condensing column, Pyrex, 2.2 For additional information see Vijan and packed with 3- to 5-mm Pyrex beads (fig. 48). Chan (1976) and Pyen and Fishman (1979). The condensing column need not be cooled. The nitrogen gas flow rate is adjusted for maximum 3. Interferences sensitivity by analyzing a series of identical 3.1 No interferences in the hydride-generation standards. A flow rate of approx 225 mL/min process have been observed from aluminum, iron, has been found satisfactory. 489 490 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Liquid stream Nj (0.11-inlD) * Tube furnace \ i u.ou-Titm \\j

Tygon tubing ^^ I

Rubber stopper r i JL • Ball and socket joint (No. 0) -^ I A

15-mm ID -^ i c f~ > c | "oi ^5 o 0 CO 0) E CO 'coc 0) 1 i 0) CO CO i § CO CO o O 1 o 0>

X* 1 I : ^J

5-mm ID -> Waste

— 3 o i Figure 48.—Stripping-condensing column and quartz tube furnace

4.5 Tube furnace, quartz, 10-mm is ubiquitous. Extreme care is required in the ID X 100-mm length with a quartz eyelet at each preparation of reagents to avoid contamination. end of tube to anchor nickel-chrome wire and Wash all glassware, including pipets, with 1:1 tube fused at the center with a 2-mm ID quartz HC1 just prior to use in tho preparation of tube. Wrap the tube furnace with 5.5 m (18 ft) reagent and standard solutions. of 26-gauge nickel-chrome wire and cover with 5.1 (Ethylenedinitrilo) tctraacetic acid, asbestos cloth. Mount lengthwise in the optical tetrasodium salt solution, 41.6 g/L: Dissolve path of the atomic absorption spectrometer. 41.6 g Na4EDTA in deminerolized water and 4.6 Technicon AutoAnalyzer II, consisting dilute to 1 L. of sampler, manifold, proportioning pump, and 5.2 Hydrochloric acid, 3Af: Add 250 mL con­ recorder. centrated HC1 (sp gr 1.19) to demineralized Cam ——————————— 20 (2/1) water and dilute to 1 L. 5.3 Nitrogen gas, N2. 5. Reagents (NOTE 1) 5.4 Sodium borohydride solution, 5 g/L: NOTE 1. Because tin is used extensively in Dissolve 5 g NaBH4 and 40 g NaOH in demin­ metal products, its occurrence in laboratories eralized water and dilute to 1 L. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 491

5.5 Tin standard solution /, 1.00 mL = 1.00 Ttn standard solution III Concentrated HCI Tin concentration mg Sn: Dissolve 1.0 g tin metal in 15 mL of aqua _____(mL)_____ (mL) frg/L) regia in a beaker. Heat to dissolve the tin metal 0.0 2.0 0 2.0 1.8 1 and evaporate just to dryness. To the residue 4.0 1.6 2 add 100 mL concentrated HCI (sp gr 1.19). Mix 10.0 1.0 5 until the residue dissolves. Transfer the solution 20.0 ! .0 10 to a volumetric flask containing demineralized water and dilute to 1,000 mL. Prepare fresh 6. Procedure each month. 6.1 Set up manifold (fig. 49). 5.6 Tin standard solution II, 1.00 mL = 10.0 6.2 Set the tube-furnace temperature at Mg Sn: Dilute 5.00 mL tin standard solution I 850 °C (about 47 V on the autotransformer) and and 50 mL concentrated HCI (sp gr 1.19) to 500 monitor using the portable pyrometer with the mL with demineralized water. Prepare fresh thermocouple placed in the center of the tube. daily. Adjust voltage on the autotransformer as ap­ 5.7 Tin standard solution III, 1.00 mL = propriate. 0.10 /ig Sn: Dilute 5.00 mL tin standard solu­ 6.3 Initially, feed all reagents through the tion II and 50 mL concentrated HCI (sp gr 1.19) system using demineralized water in the sam­ to 500 mL with demineralized water. Prepare ple line and allow the baseline to stabilize. fresh daily. 6.4 Prepare the sample trays as follows: (1) 5.8 Tin working standards: Prepare daily a In the first tray, place three tubes of the most blank and 200 mL each of a series of tin work­ concentrated standard followed by one tube ing standards by appropriate quantitative dilu­ each of the remaining standards and the blank tion of tin standard solution III and in decreasing concentrations; (2) place individ­ concentrated HCI (sp gr 1.19) as follows: ual standards of differing concentrations in LDl(in) mL/min 20-turn coils JWflflTL 1.110 3.9( Sample

Samplern 4 10.110 3.9( Air - 20/h 2/1 cam 1.056 1.21 EDTA

1.110 3.90| Sodium borohydride

1.056 l.20| Hydrochloric acid 20-turn coil 0.110 3.90 Water To sampler 4 To separator wash receptacle Proportioning pump Figure 49.—Tin, hydride manifold •• 492 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS every eighth position of the remainder of this 8. Report and subsequent trays; (3) fill remainder of each 8.1 Report tin, dissolved (01100), total- sample tray with unknown samples. recoverable (01102), and suspended-recoverable 6.5 When the baseline stabilizes, remove the (01101), concentrations as follows: less than 10 sample line from the demineralized wash solu­ /ig/L, nearest /tg/L; 10 jig/L and above, two tion and begin analysis. significant figures. 6.6 With a 5-mV recorder, 10 jtg/L of tin will 8.2 Report tin, recoverable-from-bottonv give a peak approx 60 percent of full scale. If material (01103), concentrations as follows: less the sensitivity drops by 30 percent or more, than 1.0 /xg/g, nearest 0.1 pglg; 1.0 jxg/g and replace or treat the cell by one of the following above, two significant figures. methods: 6.6.1 Soak the tube furnace for 30 min in 1:1 9. Precision water-hydrofluoric acid solution and rinse with 9.1 Determination of dissolved tin in four demineralized water. test samples 10 times each by one operator 6.6.2 Grind the cell with silicon carbide as resulted in mean values of 5.1,9.2,9.7, and 10.0, follows: Mount cell with suitable cushioning in figIL and standard deviations of 0.3, 0.3, 0.4, a %-inch chuck on a slowly-revolving shaft. Wet and 0.1, respectively. inside of cell and apply grinding compound such 9.2 Precision for dissolved! tin also may be as commercial auto-valve-grinding compound. expressed in terms of the percent relative stand­ Using a standard speed drill and an aluminum ard deviation as follows: oxide grinding wheel suitably reduced in diameter to give adequate clearance, and plen­ Number of Relative standard deviation ty of water, begin grinding cell with a steady replicates _____(percent)_____ movement from inside to outside of cell. Grind 10 5.1 6 one-half of cell at a time and regrind if necessary 10 9.2 3 to achieve an even frosting. 10 9.7 4 10 10.0 1

7. Calculations 9.3 Determination of toted recoverable tin in 7.1 Prepare an analytical curve by plotting five test samples 10 times each by one operator the height of each standard peak versus its resulted in mean values of 5.3, 9.8, 10.1, 10.5, respective tin concentration; use the value from and 11.7 /ig/L and standard deviations of 0.2, the third tube for the reading on the most con­ 0.4, 0.2, 0.3, and 0.5, respectively. centrated standard (the first two tubes usually read low). 9.4 Precision for total recoverable tin also 7.2 Determine the concentration of dis­ may be expressed in terms of the percent solved or total recoverable tin in each sample relative standard deviation as follows: by comparing its peak height to the analytical Number of Mean Rotative standard deviation curve* Any baseline drift that may occur must replicates _____(percent) _____ be taken into account when computing the 10 5.3 4 height of a sample or standard peak. 10 9.8 4 7.3 To determine micrograms per liter of 10 10.1 2 suspended recoverable tin, subtract dissolved- 10 10.5 3 tin concentration from total-recoverable-tin con­ 10 11.7 4 centration. 7.4 To determine micrograms per gram of 9.5 Determination of tin in bottom material tin in bottom material samples, first determine in four test samples 10 times each by one the micrograms per liter in each sample as in operator resulted in mean values of 0.36, 0.56, paragraph 7.2, then 0.68, and 0.94 pg/g and standard deviations of 0.04, 0.03, 0.03, and 0.02, respectively. 9.6 Precision for tin hi bottom material also SnXmL of digest/1000 Sn (figlg) = may be expressed in terms of percent relative wt of sample (g) standard deviation as follows: METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 493

Relative Number of standard deviation References replicates (percent) Pyen, G., and Fishman, M. J., 1978, Automated determina­ 10 0.36 11 tion of tin in water: Atomic Absorption Newsletter, v. 10 0.56 5 18, p. 34-26. 10 0.68 4 Vijan, P. N., and Chan, C. Y., 1976, Determination of tin by 10 0.94 2 gas phase atomization atomic absorption spectrometry: Analytical Chemistry, v. 48, p. 1788-92.

Titanium, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: Titanium, total, 1*5474-85 (mg/kg as Ti): none assigned

2. Summary of method plate at 200 °C. Titanium is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec- homogenized. The sample is digested with a trometry. See method 1-5474, metals, major and combination of nitric, hydrofluoric, and per­ minor, total-in-sediment, atomic absorption chloric acids in a Teflon beaker heated on a hot spectrometric, direct. 495

Turbidity, nephelome^ric

Parameter and Code: Turbidity, 1-3860-85 (nephelometric turbidity! unit): 00076

1. Application 3. Interferences This method is generally applicable to any The presence of colored solutes causes water that does not contain coarse material that measured turbidity values to be low. Precip­ settles rapidly. Samples having greater than itation of dissolved constituents (for example, 100 nephelometric turbidity units (NTU) must Fe) causes measured turbidity values to be be diluted prior to analysis. high.

2. Summary of method 4. Apparatus 2.1 The method presented below is based Hack turbidimeter, Model No. 2100 or 2100A. upon a comparison of the intensity of light scat­ tered by the sample under defined conditions with the intensity of light scattered by a stand­ 5. Reagents ard reference suspension under the same condi­ 5.1 Hexamethylenetetramine solution, 10 tions. The greater the intensity of scattered g/100 mL: Dissolve 10.0 g hexamethylene- light, the greater the turbidity. Formazin poly­ tetramine in demineralized water and dilute to mer, which has gained acceptance as the turbidi­ 100.0 mL. ty standard reference suspension in the brewing 5.2 Hydrazine sulfate solution, 1 g/100 mL: industry, is also used as the turbidity standard Dissolve 1.000 g (NH2)2-H2SO4 in demineral­ reference suspension for water. It is easy to pre­ ized water and dilute to 100.0 mL. pare and is more reproducible in its light-scatter 5.3 Turbidity standard suspension I (For­ ing properties than is clay or turbid, mazin): In a 100-mL volumetric flask mix 5.0 natural-water standards. The turbidity of a par­ mL hydrazine sulfate solution with 5.0 mL hex- ticular concentration of Formazin suspension is amethylenetetramine solution. After 24 h stand­ defined as 40 NTU. This same suspension of ing at 25±3°C, dilute to 100.0 mL with Formazin has a turbidity of approximately 40 demineralized water and mix well. Prep tare fresh units when measured on the Jackson candle tur- monthly (NOTE 1). bidimeter; therefore, turbidity units based on NOTE 1. Prepared standards of several ranges the Formazin preparation will closely approx­ are available from the instrument manufac­ imate those derived from the Jackson candle turer. These have a reliable shelf life of 4 to 6 turbidimeter but may not always be identical months, thereby making more frequent, prepara­ to them. tion unnecessary. 2.2 For additional information on the tur­ 5.4 Turbidity standard suspension II: Dilute bidity measurement and its significance, see 10.0 mL turbidity standard suspension I to American Public Health Association and others 100.0 mL with demineralized water. The turbidi­ (1980), California State Water Quality Control ty of this suspension is defined as 40 Board (1963), and U.S. Public Health Service nephelometric turbidity units (NTU). Prepare (1962). fresh weekly. This suspension may be diluted

497 498 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS as required to prepare more dilute turbidity 7. Calculations standards. Turbidity (NTU) = 6. Procedure final ciilution volume observed turbidity X 6.1 Turbidimeter calibration: The manu­ original sample volume facturer's operating instructions should be followed. Measure the standards on the tur- 8. Report bidimeter covering the range of 0 to 100 NTU. Report turbidity (00076) as follows: less than If the instrument is already calibrated in 10 NTU, one decimal; 10 NTU and above, two standard turbidity units, this procedure will significant figures. check the accuracy of the calibration. At least one standard should be included for each 9. Precision instrument range to be used. Some instruments According to data reported! by the U.S. En­ permit adjustment of sensitivity so that scale vironmental Protection Agency, the precision values will correspond to turbidities. Reliance of data from a single laboratory expressed in on a manufacturer's solid-scattering standard terms of the percent relative sltondard deviation for setting overall instrument sensitivity for is as follows: all ranges is not an acceptable practice unless the turbidimeter has b$en shown to be free of Relative standard devlatlo drift on all ranges. If a pre-calibrated scale (NTU) (percent)____ is not supplied, then a calibration graph should 0.26 be prepared for each range of the instrument. 6.2 Turbidity less than 100 NTU: Shake the References sample to disperse the solids thoroughly. Wait American Public Health Association and others, 1980, until air bubbles disappear; then pour the sam­ Standard methods for the examination of water and ple into the turbidimeter tube. Read the turbidi­ wastewater 15th ed. : Washington, D.C., p. 132-4. ty directly from the instrument scale or from California State Water Quality Control Board, 1963, Water the appropriate calibration curve. quality criteria: Publication 3-A, p. 290. 6.3 Turbidity exceeding 100 NTU: Dilute U.S. Environmental Protection Agency, 1979, Methods for chemical analysis of water and wastes: Cincinnati, the sample with one or more volumes of p. 180.1-1. nonturbid water until the turbidity falls below U.S. Public Health Service, 1962, Drinking water standards: 100 NTU. Public Health Service Publication 956, p. 6. Vanadium, colorimetric, catalytic oxidation

Parameter and Code: Vanadium, dissolved, 1-1880-85 (pg/L as V): 01085

1. Application 4. Apparatus This method may be used to analyze most 4.1 Water bath, regulated to 25 + 0.5 °C. waters containing from 0.5 to 5.0 /*g/L of 4.2 Spectrometer, for use at 415 nm. Refer vanadium, provided that the interferences iden­ to manufacturer's manual for optimizing in­ tified below are not exceeded. By reducing the strumental parameters. reaction time, concentrations up to 100 /ig/L may be determined. 5. Reagents 5.1 Ammonium persulfate-phosphoric acid 2. Summary of method reagent: Dissolve 2.5 g (NH4)2S2O8 in 25 mL 2.1 The oxidation of gallic acid by acid- demineralized water. Heat solution to just persulf ate is catalyzed by the presence of small below boiling, remove from heat, and add an amounts of vanadium (Jarabin and Szarvas, equal volume of concentrated H3PO4 (sp gr 1961). Depending on the amount of vanadium 1.69). Let stand for approx 24 h before using. present, the reaction produces a yellow-to-red col­ Discard after 2 days. or, the absorbance of which is measured spec- 5.2 Gallic acid solution, 1 g/100 mL: trometrically at 415 nnx Under given conditions Dissolve 0.5 g gallic acid in 50 mL hot deminer­ of reactant concentration, temperature; and reac­ alized water and filter through Whatman No. tion time, the extent of oxidation of gallic acid 42 filter paper. Prepare fresh daily. is proportional to the concentration of vanadium 5.3 Mercuric nitrate solution, 332 mg/L: present (Fishman and Skougstad, 1964). Dissolve 0.350 g Hg(NO3)2-H2O in demineral­ 2.2 This method is essentially the same as ized water and dilute to 1 L. that reported by the American Society for 5.4 Vanadium standard solution I, 1.00 Testing and Materials (1984). mL = 100 A*g V: Dissolve 0.2309 g ainmonium metavanadate (NH4VO3) in demineralized 3. Interferences water and dilute to 1,000 mL. 3.1 Several substances interfere, including 5.5 Vanadium standard solution II, 1.00 chloride above 100 mg/L and bromide and iodide mL = 1.0 /ig V: Dilute 10.0 mL vanadium at lower concentrations. Their interference is standard solution I to 1,000 mL with deminer­ eliminated or minimized by the addition of mer­ alized water. curic nitrate solution. In the presence of mer­ 5.6 Vanadium standard solution III, LOO curic nitrate, concentrations of 100 mg/L Cl"1, mL = 0.01 /|g V: Immediately before use, dilute 0.25 mg/L Br'1, and 0.25 mg/L I'1 can be 10.0 mL vanadium standard solution II to 1,000 tolerated. The following ions interfere when the mL with demineralized water. This standard is indicated concentrations are exceeded: silver, used to prepare working standards at time of 2,000 j*g/L; cobalt, 1,000 fig/L; nickel, 3,000 analysis. jig/L; copper, 50 /ig/L; chromium, 1,000 /ig/L; and ferrous iron, 300 j*g/L. 6. Procedure 3.2 Nitric acid causes erratic and uncertain 6.1 Pipet a volume of sample containing less results. than 0.05 /ig V (10.0 mL max) into a 23-mm 499 500 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS absorbance cell or a 25-mL test tube, and ad­ 1,000 V (/xg/L) = X jig V in sample just the volume to 10.0 mL. mL sample 6.2 Prepare a blank and sufficient standards containing from 0.01 to 0.05 fig V in 23-mm ab­ sorbance cells or 25-mL test tubes, and adjust 8. Report the volume of each to 10.0 mL with demineral- Report vanadium, dissolved (01085), concen­ ized water. (Standards must be included with trations as follows: less than 10 jig/L, 1 jig/L; each set of samples.) 10 /*g/L and above, two significant figures. 6.3 Add 1.0 mL mercuric nitrate solution to samples, standards, and blank, and place all cells or test tubes in a water bath (25 °C). Allow 9* Precision 9.1 Precision for dissolved vanadium within 30 to 45 min for samples to reach temperature its designated range may Ibe expressed as equilibrium. follows (American Society for Testing and 6.4 Add 1.0 mL ammonium persulfate- Materials, 1984): phosphoric acid reagent (temperature equi­ librated). Mix and return to water bath. 6.5 Add 1.0 mL gallic acid (temperature ST = 0.069-Y + 0.422 equilibrated). Mix and return to water bath (NOTE 1). where NOTE 1. Because time and temperature are ST = overall precision, micrograms per liter, critical factors, the absorbance of each sample and must be measured exactly 60 rnm after the X = concentration of vanaclium, micrograms gallic acid is added. Time the analyses of several per liter. samples most easily by starting a stopwatch 9.2 Precision for dissolve*! vanadium for with the addition of gallic acid to the first sam­ four samples expressed in terms of percent ple and by adding the gallic acid to subsequent relative standard deviation is as follows: samples at appropriate intervals. 6.6 After about 58 min, remove all cells or test tubes from the water bath; and at exactly Number of Mean Relative standard deviation 60 min, measure the absorbance at 415 nm, laboratories _____(percent)_____ using demineralized water as a reference 3 1.3 46 (NOTE 2). 3 2.3 65 3 6.7 31 NOTE 2. All samples may be removed from the 3 12.6 57 water bath 1 or 2 min before the end of the 60-min period. The samples are then prepared for measurement, and the absorbance of each References sample is measured exactly 60 ™in after the ad­ American Society for Testing and Materials, 1984, Annual dition of the gallic acid. book of ASTM standards, section 31, water: Philadel­ phia, v. 1101, p. 676-81. 7. Calculations Fishman, M. J., and Skougstad, M. W., 1964, Catalytic 7.1 Determine micrograms of vanadium in determination of vanadium in water: Analytical each sample from a plot of absorbances of Chemistry, v. 36, p. 1643-6. Jarabin, Z., and Szarvas, P., 1961, Detection of small standards. amounts of vanadium by catalytic reaction with the ad­ 7.2 Determine the concentration of dition of gallic acid: Acta University Debrecen, v. 7, vanadium in micrograms per liter as follows: p. 131; Chemical Abstracts, 1962, v. 57, 9192c. Vanadium, colorimetric, catalytic oxidation, automated-segmented flow

Parameter and Code: Vanadium, dissolved, 1-2880-85 fog/L as V): 01085

1. Application Absorption cell —————— 15 mm This method may be used to analyze most Wavelength ———————— 410 nm waters containing from 1 to 10 /*g/L vanadium, Cam ————————————— 20/h (1/1) provided that the interferences identified below Water-bath temperature — 60 °C are not exceeded. 5. Reagents 2. Summary of method 5.1 Amntonium persulfate-phosphoric acid Low concentrations of vanadium catalyze the reagent: Dissolve 2.5 g (NH4)2S2O8 in 25 mL acid-persulfate oxidation of gallic acid. This demineralized water. Heat solution to just reaction proceeds rapidly in the presence of below boiling, remove from heat, and add an vanadium but only very slowly in its absence. equal volume of concentrated H3PO4 (sp gr The amount of colored oxidation product 1.69). Let stand for approx 24 h before use. formed by this reaction is directly propor­ Before use, dilute with 50 mL demineralized tional to the concentration of vanadium when water. Discard after 2 days. temperature, reaction time, and concentration 5.2 Gallic acid solution, 20 g/L: Dissolve 5 of reactants are carefully controlled (Fishman g gallic acid in 250 mL hot, demineralized water and Skougstad, 1964; Jarabin and Szarvas, and filter through paper (Whatman No. 42 or 1961). equivalent). Prepare fresh daily. Keep the solu­ tion warm during analysis to prevent the gallic 3. Interferences acid from precipitating. 3.1 Chloride, bromide, and iodide interfere 5.3 Mercuric nitrate solution, 332 mg/L: when their concentrations exceed 100 mg/L, 10 Dissolve 350 mg Hg(NO3)2*H2O in deioineral* jig/L, and 1 ngfL, respectively. Iron(II), iron(III), ized water and dilute to 1 L. and copper(II) interfere when their concentra­ 5.4 Vanadium standard solution I, 1.00 tions exceed 300 /ig/L, 500 /ig/L, and 50 /*g/L, mL = 100 fig V: Dissolve 0.2309 g amxnonium respectively. The concentrations of other ions metavanadate (NH4VO3) in demin&ralized are rarely high enough to interfere. water and dilute to 1,000 mL. 3.2 Nitric acid causes erratic and uncertain 5.5 Vanadium standard solution II, 1.00 results. mL = 1.0 pg V: Dilute 10.0 mL vanadium standard solution I to 1,000 mL with deminer­ 4. Apparatus alized water. 4.1 Technicon AutoAnalyzer II, consisting 5.6 Vanadium standard solution III, 1.00 of sampler, proportioning pump, cartridge man­ mL = 0.05 jig V: Dilute 50.0 mL vanadium ifold, water bath, colorimeter, voltage stabilizer, standard solution II to 1,000 mL with demin­ recorder, and printer. eralized water. 4.2 With this equipment the following oper­ 5.7 Vanadium working standards: Prepare ating conditions have been found satisfactory a blank and 250 mL each of a series of vanadium for the range from 1 to 10 /tg/L vanadium. working standards by appropriate quantitative 501 502 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS dilution of vanadium standard solution III as tray, beginning with the most concentrated follows: standard. Place individual standards of dif­ fering concentrations in approx every eighth Vanadium standard solution III Vanadium concentration position of the remainder of this and subsequent (mL) sample trays. Fill remainder of each tray with 0.0 0.0 5.0 1.0 unknown samples. 10.0 2.0 6.5 Begin analysis. When the peak from the 20.0 4.0 most concentrated standard appears on the 30.0 6.0 40.0 8.0 recorder, adjust the STD CAL control until the 50.0 10.0 flat portion of the peak reads full scale.

6. Procedure 7. Calculations 6.1 Set up manifold (fig. 50). 7.1 Prepare an analytical <:urve by plotting 6.2 Allow colorimeter, recorder, and water the height of each standard peak versus its bath to warm for at least 30 min or until the respective vanadium concentration. temperature of the water bath reaches 60 °C. 7.2 Compute the concentration of vanadium 6.3 Adjust the baseline to read zero scale in each sample by comparing its peak height to divisions on the recorder with all reagents, but the analytical curve. Any baseline drift that with demineralized water in the sample line. may occur must be taken into account when 6.4 Place a complete set of standards and a computing the height of a sample or standard blank in the first positions of the first sample peak.

Waste G3 Proportioning pump

To sampler 4 0.073in Wash wash 2.00 mL/min 0.030 in Air 0.32 mL/min 0.056in Sample 1.20 mL/min Gallic acid 0.025 in Sampler 4 0.23 mL/min Acid- 207 h pers.lfate 0.025in 1/lcam 0.23 mL/min 0.030in Air 0.32 mL/min 0.045 in Resanple 0.80 mL/min 0.025in Mercuric nitrate 0.23 mL/min O.OSlin Waste 1.00 mL/min

Recorder

Figure 50.—Vanadium, catalytic oxidation manifold METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 503

8. Report Number of Mean Relative standard deviation Report vanadium, dissolved (01085), concen­ replicates _____(percent)_____ trations as follows: less than 10 ^g/L, nearest 4 3.5 3 8 8.1 I 1 Mg/L; 10 ftg/L and above, two significant 8 53.9 I figures. References Fishman, M. J., and Skougstad, M. W.t 1964, Catalytic 9. Precision determination of vanadium in water: Analytical Single-operator precision for dissolved Chemistry, v. 36, p. 1643-6. Jarabin, Z., and Szarvas, P., 1961, Detection of small vanadium for three samples expressed in terms amounts of vanadium by catalytic reaction with the ad­ of percent relative standard deviation is as dition of gallic acid: Acta University Debrecen, v. 7, follows: p. 131; Chemical Abstracts, 1962, v. 57, 9192c.

Vanadium, atomic emission spectrometric, ICP i Parameter and Code: Vanadium, dissolved, 1-1472-85 faglL as V): 01085

2. Summary of method method utilizing an induction-coupled argon Vanadium is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 505

Zinc, atomic absorption spectrometric, direct

Parameters and Codes: Zinc, dissolved, 1-1900*85 fog/l as Zn): 01090 Zinc, total recoverable, I-3900-85 (/xg/L as Zn): 01092 Zinc, suspended recoverable, I-7900-85 fcig/L as Zn): 01091 Zinc, recoverable-from-bottom-material, dry wt, I-5900-85 0*g/g as Zn): 01093

1. Application copper, lead, cobalt, and chromium (10,000 jtg/L 1.1 This method may be used to analyze water each) do not interfere. Greater concentrations and water-suspended sediment containing from of each constituent were not investigated. 10 to 500 /ig/L of zinc. Sample solutions contain­ 3.3 Samples containing 100 mg/L of silica ing more than 500 /ig/L need to be diluted or to cause no interference; however, zinc recovery is be read on a less expanded scale. approx 10 percent low in samples containing 1.2 Suspended-recoverable zinc is calculated 200 mg/L of silica. by subtracting dissolved zinc from total recoverable zinc. 4. Apparatus 1.3 This method may be used to analyze bot­ 4.1 Atomic absorption spectrometer tom material containing at least 1.0 uglg of zinc. equipped with electronic digital readout and Sample solutions containing more than 500 automatic zero and concentration controls. jig/L of zinc need to be diluted or less scale ex­ 4.2 Refer to the manufacturer's manual to pansion used. optimize instrument for the following: 1.4 Total recoverable zinc in water-sus­ Grating ———————— Ultraviolet pended sediment needs to undergo preliminary Wavelength ————— 213.8 nm digestion-solubilization by method 1-3485, and Source (hollow-cathode recoverable zinc in bottom material needs to lamp) ———————— Zinc undergo preliminary digestion-solubilization by Oxidant ———————— Air method 1-5485 before being determined. Fuel ————————— Acetylene Type of flame ———— Oxidizing 2. Summary of method 4.3 The 50-mm (2-in.) and 100-mm (4-in.) 2.1 Zinc is determined by atomic absorption flathead, single-slot burners allow a working spectrometry by direct aspiration of the sam­ range from 10 to 500 /ig/L of zinc. Different ple into an air-acetylene flame. burners may be used according to manufac­ 2.2 The procedure may be automated by the turer's instructions. addition of a sampler and either a strip-chart recorder or a printer or both. 5. Reagents 5.1 Zinc standard solution 1, 1.00 mL - 100 3. Interferences j*g Zn: Dissolve 0.100 g reagent grade zinc 3.1 Magnesium at concentrations greater (30-mesh) in a slight excess of concentrated HC1 than 100 mg/L interferes unless other cations, (sp gr 1.19), and dilute to 1,000 mL with demin- such as sodium, are present in the sample. eralized water. 3.2 Individual concentrations of sodium, 5.2 Zinc standard solution II, 1.00 mL = 1.0 potassium, sulfate, chloride (9,000 mg/L of Vg Zn: Dilute 10.0 mL zinc standard solution I each), calcium (4,500 mg/L), nitrate (2,000 to 1,000 r>VL with demineralized water contain­ mg/L), iron (4 X 106 ptg/L), and cadmium, nickel, ing 1 mL concentrated HNO3 (sp gr 1.41). 507 508 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5.3 Zinc working standards: Prepare a series than 10 uglg, nearest microgram per gram; 10 of at least six working standards containing /ig/g and above, two significant figures. from 10 to 500 jig/L of zinc by appropriate dilu­ tions of zinc standard solution II with acidified 9. Precision water. 9.1 Precision for dissolved zinc for 30 5.4 Water, acidified. Add 1.5 mL concen­ samples within the range of 14 to 1110 /ig/L trated HNO3 (sp gr 1.41) to 1 L of demineral- may be expressed as follows: ized water. ST = 0.070X + 6.51 6. Procedure Aspirate the blank (acidified water) to set the where automatic zero control. Use the automatic con­ ST = overall precision, micrograms per liter, centration control to set the concentrations of and standards. Use at least six standards. Calibrate X — concentration of zinc, micrograms per the instrument each time a set of samples is liter. analyzed and check calibration at reasonable The correlation coefficient is 0.7967. intervals. 9.2 Precision for dissolved zinc for six of the 30 samples expressed in terms of the percent 7. Calculations relative standard deviation is as follows: 7.1 Determine the micrograms per liter of Number of Mean Relative standard deviation dissolved or total recoverable zinc in each sam­ laboratories (MQ/L) _____(percent)_____ ple from the digital display or printer output 33 14 43 while aspirating each sample. Dilute those 47 104 10 samples whose zinc concentrations exceed the 19 116 22 working range of the method and multiply by 41 236 7 22 520 5 the proper dilution factors. 17 1110 9 7.2 To determine micrograms per liter of suspended recoverable zone, subtract dissolved- 9.3 It is estimated that the percent relative zinc concentration from total-recoverable-zinc standard deviation for total recoverable and concentration. suspended recoverable zinc and recoverable zinc 7.3 To determine micrograms per gram of in bottom material will be i?eater than that zinc in bottom-material samples, first determine reported for dissolved zinc. the micrograms per liter of zinc as in paragraph 9.4 Precision for total recoverable zinc ex­ 7.1, then pressed in terms of the percent relative stand­ mL of original digest ard deviation for two water-suspended sediment ftg/L of Zn X mixtures is as follows: Zn (Mg/g) = ____1.000 Number of Relative standard deviation wt of sample (g) laboratories (MO/L) ____(percent)____ 23 78.4 27 8. Report 26 172 31 8.1 Report zinc, dissolved (01090), total- recoverable (01092), and suspended- recoverable (01091), concentrations as follows: less than 100 Reference Mg/L, nearest 10 /ig/L; 100 figlL and above, two Fishman, M. J., and Downs, S. C, 1966, Methods for significant figures. analysis of selected metals in water by atomic absorp­ 8.2 Report zinc, recoverable-from-bottom- tion: United States Geological Survey Water-Supply material (01093), concentrations as follows: less Paper 1540-C., p. 43-5. Zinc, atomic absorption spectrometric, graphite furnace

Parameter and Code: Zinc, dissolved, 1-1901*65 (/ig/L as Zn): 01090

1. Application chloride (25 mg/L) do not interfere. Greater con­ 1.1 This method may be used to determine centrations of these constituents were not in­ zinc in low ionic-strength water and precipita­ vestigated. tion. With Zeeman background correction and 3.2 Precipitation samples usually contain a 20-/*L sample, the method is applicable in the very low concentrations of zinc. Specud precau­ range from 0.5 to 40 /ig/L. Sample solutions that tionary measures must be employed during contain zinc concentrations exceeding the up­ both sample collection and laboratory deter­ per limits must be diluted or preferably be mination to prevent contamination. analyzed by the atomic absorption spectro­ metric method, or by the atomic emission spec- 4. Apparatus trometry ICP method. 4.1 Atomic absorption spectrometer, for use 1.2 The analytical range and detection limits at 213.8 nm and equipped with background cor­ can be increased or possibly decreased by vary­ rection, digital integrator to quantitate peak ing the volume of sample injected or the in­ areas, graphite furnace with temperature pro­ strumental settings. Purification of reagents grammer, and automatic sample injector. The and use of ASTM Type 1 water (Method programmer must have high-temperature ramp­ D-1193, American Society for Testing and ing and stopped-flow capabilities. Materials, 1984) may result in lower detection 4.1.1 Refer to the manufacturer's manual to limits. optimize instrumental performance. The analytical ranges reported in paragraph 1,1 are 2. Summary of method for a 20-/iL sample with 5 j*L of matrix: modifier Zinc is determined by atomic absorption spec- (NOTE 1). trometry in conjunction with a graphite furnace NOTE 1. A 20-pL sample generally requires 30 containing a graphite platform (Hinderberger s to dry. Samples that have a complex matrix and others, 1981). A sample is placed on the may require a longer drying and charring time. graphite platform and a matrix modifier is 4.1.2 Graphite furnace, capable of reaching added. The sample is then evaporated to dry- temperatures sufficient to atomize the element ness, charred, and atomized using high- of interest. Warning: dial settings frequently temperature ramping. The absorption signal are inaccurate and newly conditioned furnaces generated during atomization is recorded and require temperature calibration. compared with standards. 4.1.3 Graphite tubes and platforms. Pyro- lytically coated graphite tubes and solid pyro- 3. Interferences lytic graphite platforms are recommended. 3.1 Interferences in low ionic-strength 4.2 Lab ware. Many trace metals at very low samples, such as precipitation, normally are concentrations have been found to sorb very quite low. In addition, the use of the graphite rapidly to glassware. To preclude this, fluori- platform reduces the effects of many inter­ nated ethylene propylene (FEP) or Teflon lab- ferences. Calcium (25 mg/L), magnesium (8 ware mayi be used. Alternately, glassware, mg/L), sodium (20 mg/L), sulfate (34 mg/L), and particularly flasks and pipets, may be treated 509 510 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS with silicone anti-wetting agent such as Surfacil signal should not increase by more than 0.001 (Pierce Chemical Co., Bockford, IL, 61105) ac­ absorbance-seconds. cording to the manufacturer's instructions. 5.3 Water, acidified, Type 1: Add 1.5 mL Autosampler cups must be checked for con­ high-purity, concentrated HNO3 (sp gr 1.41) to tamination. Lancer (1831 Olive St., St. Louis, each liter of water. MO, 63103) polystyrene disposable cups have 5.4 Water, Type 1. been found to be satisfactory after acid rinsing. 5.5 Zinc standard solution I, 1.00 mL = Alternately, reuseable Teflon or FEP cups may 1,000 fig Zn: Dissolve 1.0000 g Zn powder in a be used. minimum of dilute HNO3. Heat to increase rate 4.3 Argon, standard, welder's grade, com­ of dissolution. Add 10 mL higla-purity, concen­ mercially available. Nitrogen may also be used trated HNO3 (sp gr 1.41) Ultrex or equivalent if recommended by the instrument and dilute to 1,000 mL with Type 1 water. Alter­ manufacturer. natively, a certified standard solution at this concentration may be purchased. 5. Reagents 5.6 Zinc standard solution II, 1.00 mL = 5.1 Matrix modifier solution, 40g 10.0 jig Zn: Dilute 10.0 mL zinc standard solu­ NH4H2PO4/L: Add 40.0 g NH4H2PO4 to 950 tion I to 1,000 mL (NOTE 3), mL Type 1 water, mix, and dilute to 1,000 mL. NOTE 3. Use acidified, Type 1 water (paragraph Analyze 20 /*L of matrix modifier for zinc con­ 5.3) to make dilutions. All steindards must be tamination. If the zinc reading is more than stored in sealed Teflon or FEP containers. Each 0.005 absorbance-seconds, purify the solution container must be rinsed twice with a small by chelation with ammonium pyrrolidine dithio- volume of standard before being filled. Stand­ carbamate (APDC) and extraction with methyl ards stored for 6 months in FEP containers isobutyl ketone (MIBK, NOTE 2). Analyze 20 yielded values equal to those of freshly prepared /*L of the purified solution. Repeat extractions standards. until the zinc level is reduced to the acceptable 5.7 Zinc standard solution III, 1.00 level. DO NOT ADD ACID TO THE PURI­ mL = 1.00 /ig Zn: Dilute 100.0 mL zinc stand­ FIED MATRIX MODIFIER SOLUTION. ard solution II to 1,000 mL. This standard is NOTE 2. To purify matrix modifier solution, used to prepare working standards serially at pour the solution into a Teflon or FEP con­ time of analysis. tainer. Add 0.25 g APDC for each liter of solu­ 5.8 Zinc standard solution IV, 1.00 mL = tion. While stirring, adjust the solution to pH 0.010 /tg Zn: Dilute 10.0 mL zinc standard solu­ 2.9 by dropwise addition of concentrated HNO3 tion III to 1,000 mL. This standard also is used (sp gr 1*41). Transfer portions of the solution to prepare working standards serially at time to a separatory funnel, add 100 mL MIBK/liter of analysis. of solution, and shake vigorously for at least 5 min. Frequently, vent the funnel in a hood. Col­ 6. Procedure lect the extracted solution in the FEP container. 6.1 Systematically dean imd rinse work Repeat the extraction with 50 mL MIBK/liter areas with deionized water on a regular of solution. Because MIBK can dissolve some schedule. Use a laminar flow hood or a "clean plastic autosampler cups, boil the solution for room" environment during siimple transfers. at least 10 min in a silicone-treated or acid- Ideally, the autosampler and the graphite fur­ rinsed container covered with a watchglass to nace should be in a clean environment. remove MIBK. 6.2 Soak autosampler cups at least over­ 5.2 Nitric acid, concentrated, high-purity, night in a 1 + 1 solution of TS^pe 1 water and (sp gr 1.41): J. T. Baker "Ultrex" brand HN3 high-purity nitric acid. has been found to be adequately pure; however, 6.3 Rinse the sample cups twice with sam­ each lot must be checked for contamination. ple before filling. Place cups in sample tray and Analyze acidified Type 1 water for zinc. Add an cover. Adjust sampler so that only the injection additional 1.5 mL of concentrated HNO3/liter tip contacts the sample. of water, and repeat analysis. The integrated 6.4 In sequence, inject 20-/tL aliquots of METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 511 blank and working standards plus 5 jiL of /iS/cm). A known amount of zinc was added to modifier each and analyze. Analyze the blank each sample, and single-operator precision and and working standards twice. Construct the bias for six replicates are as follows: analytical curve from the integrated peak areas (absorbance-seconds). Generally, the curve Relative Amount Standard standard should be linear up to a peak-absorbance (peak- found deviation deviation height) value of 0.40 absorbance units. 0*Q/L> (percent) (percent) 6.5 Similarly, inject and analyze the samples Deionized water twice. Every tenth sample cup should contain 3.05 4.20 1.16 27.6 138 either a standard or a reference material. 5.5 5.53 .86 15.6 101 6.6 Restandardize as required. Minor 6.1 6.13 .63 10.3 100 11 11.30 .62 5.5 103 changes of values for known samples usually in­ 36 39.95 4.51 11.3 111 dicate deterioration of the furnace tube, contact rings, and/or platform. A major variation usual­ Tap water (NOTE 4) ly indicates either autosampler malfunction or 3.05 2.17 .73 7.2 71 residue buildup from a complex matrix in a 5.5 4.27 .65 5.3 78 6.1 6.38 1.44 10.1 105 previous sample. 11 8.85 .92 5.5 80 36 42.93 4.67 10.0 119 7. Calculations Determine the micrograms per liter of zinc in NOTE 4. The tap water contained 8 /ig/L of zinc, each sample from the digital display or printer and the standard deviation and percent relative output. Dilute those samples containing concen­ standard deviation were calculated prior to sub­ trations of zinc that exceed the working range traction of zinc originally present. of the method; repeat the analysis, and multi­ ply by the proper dilution factors. References American Society for Testing and Materials, 1984, Annual 8. Report book of ASTM Standards, section llt water: Philadel­ Report zinc, dissolved (01090), concentrations phia, v. 11.01, p. 39-42. as follows: less than 10.0 /*g/L, nearest 0.1 /xg/L; Cooksey, M., and Barnett, W. B., 1979, Matrix modifica­ 10 jig/L and above, two significant figures. tion and the method of additions in flameless atomic absorption: Atomic Absorption Newsletter, v. 18, p. 101-5. 9. Precision Feroandez, F. J., Beatty, M. M., and Barnett, W. B., 1981, 9.1 Analysis of four samples by a single Use of the L'vov platform for furnace atomic absorp­ operator using Zeeman background correction tion applications: Atomic Spectroscopy, v. 2, p. 16-21. is as follows: Hinderberger, E. J., Kaiser, M. L., and Koirtyohann, S. R., 1981, Furnace atomic absorption analysis of biological Relative samples using the LVov platform and matrix modifica­ standard tion: Atomic Spectroscopy, v. 2, p. 1-11. Number of Standard deviation replicates (percent) Manning, D. C., and Slavin, W., 1983, The determination of trace elements hi natural waters using the stabilized 6 5.92 0.24 4.1 temperature platform furnace: Applied Spectroscopy, 4 16.02 .26 1.6 6 19.70 1.29 6.5 v. 37, p. 1-11. 12 40.21 3.18 7.9 Ottaway, J. M., 1982, A revolutionary development in graphite furnace atomic absorption: Atomic Spec­ troscopy, v. 3, p. 89-92. Slavin, W., Carnrick, G. R., and Manning, D. C., 1982, 9.2 The precision and bias for the Zeeman Magnesium nitrate as a matrix modifier in tho stabilized background correction were tested on deionized temperature platform furnace: Analytical Chemistry, water and tap water (specific conductance 280 v. 54, p. 621-4.

Zinc, atomic emission spectrometric, ICP

Parameter and Code: ; Zinc, dissolved, 1-1472-85 btg/L as Zn): 01090

2. Summary of method method utilizing an induction-coupled argon Zinc is determined simultaneously with plasma as an excitation source. See method several other constituents on a single sample 1-1472, metals, atomic emission spectrometric, by a direct-reading emission spectrometric ICP. 513

Zinc, total-in-sediment, atomic absorption spectrometric, direct

Parameter and Code: j Zinc, total, 1-5474-85 (mg/kg as Zn): none assigned

2. Summary of method hotplate at 200 °C. Zinc is determined on the A sediment sample is dried, ground, and resulting solution by atomic absorption spec- homogenized. The sample is digested with a trometry. See method 1-5474, metals, major and combination of nitric, hydrofluoric, and per­ minor, total-in-sediment, atomic ab sorption chloric acids in a Teflon beaker heated on a spectrometric, direct. 515

Metals, atomic emission spectrometric, ICP

Parameters and Codes: Metals, dissolved, 1-1472-85 (see below)

Parameter Code Parameter j Code Barium (/tg/L as Ba) 01005 Magnesium (mg/L as Mg) 00925 Beryllium (/*g/L as Be) 01010 Manganese fcg/L as Mn) 01056 Cadmium fcg/L as Cd) 01025 Molybdenum fc*g/L as Mo) 01060 Calcium (mg/L as Ca) 00915 Silica (mg/L as SiO2) 00955 Cobalt (fjiQlL as Co) 01035 Sodium (mg/L as Na) 00930 Copper (/*g/L as Cu) 01040 Strontium fcg/L as Sr) 01080 Iron (fiQlL as Fe) 01046 Vanadium fcg/L as V) 01085 Lead faQlL as Pb) 01049 Zinc fcg/L as Zn) 01090 Lithium fcg/L as Li) 01130

1. Application dorsement of one product over another, but 1.1 This method may be used only for the rather, acknowledges that ICP technology is determination of dissolved constituents in rapidly changing and developing. water that have a measured specific conduc­ tance of less than 2,000 /iS/cm at 25 °C. Table 2. Summary of method 8 specifies the upper and lower concentration All parameters are determined simultaneous­ limits. Samples containing analyte concentra­ ly on a single sample by a direct-reading emis­ tions greater than the upper concentration limit sion spectrometric method utilizing an may be analyzed for calcium, magnesium, silica, induction-coupled argon plasma as an excitation and sodium if the sample is diluted and if, after source. Samples are pumped into a pneumatic dilution, the specific conductance is below 2,000 nebulizer, atomized, and introduced iinto the /iS/cm. Trace metals can also be determined in plasma via a spray chamber and torch assem­ samples that have a measured specific conduc­ bly. Each analysis is determined on the basis tance greater than 2,000 /*S/cm by dilution; of the average of two replicate exposures, each however, detection levels and sensitivity will of which is background-corrected by a spec­ change proportionally. trum-shifting technique. Calibration is per­ 1.2 Analyses must be performed on filtered formed by standardizing with a series of four and acidified samples. Water-suspended sedi­ mixed-element standards and a blank, ment and bottom material cannot be analyzed. 1.3 The induction-coupled argon plasma (ICP) 3. Interferences technology is so new that instruments and 3.1 Several interelement-interference effects associated data-processing equipment and soft­ have been evaluated. Interelement-correction ware available on the commercial market are factors have been programmed into the not standardized and operating conditions vary. proprietary-data-system software and. correc­ Until operating conditions of various manufac­ tions are automatically applied, internally, to turers' instruments become more comparable the data before they are printed as output. and the equivalency of methods using those in­ 3.2 Samples containing high dissolved solids struments are established by extensive testing, exhibit a variety of unidentified interference ef­ the ICP methods approved for U.S. Geological fects. Therefore, analyses must be limited to Survey use will specify instrument and associ­ samples with a specific conductance of 2,000 ated software brands. This does not imply en­ jiS/cm or less. 517 518 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Table 8.—Working ranges of constituents for ICP

Lower limit (^g/L Upper limit 0*g/L Constituent except where noted) except where noted) Wavelength (nm) Barium 2 10,000 455.5 Beryllium .5 10,000 313.0 Cadmium 1 10,000 ;>14.4 Calcium (1) .02 mg/L 100 mg/L 396.8 Calcium (2) 100 mg/L 1,000 mg/L 315.8 Cobalt 3 10,000 ms Copper 10 10,000 324.7 Iron 3 10,000 259.9 Lead 10 10,000 220.3 Lithium 4 100,000 670.7 Magnesium (1) .001 mg/L 5 mg/L 279.5 Magnesium (2) 5 mg/L 100 mg/L 382.9 Manganese 1 10,000 257.6 Molybdenum 10 10,000 203.8 Silica (SiO2) .009 mg/L 100 mg/L 288.1 Sodium (1) .2 mg/L 100 mg/L 589.0 Sodium (2) 100 mg/L 1,000 mg/L 330.2 Strontium .5 10,000 421.5 Vanadium 6 10,000 292.4 Zinc 3 10,000 206.0* *Second order.

Orifice 1.5-mm ID o 20 mm Q 18-mm ID j^ 20-mm OD 20 mm 14-mm ID 16-mm OD

60 mm - 9-mm ID 11-mm OD Figure 51.—Block diagram of spectrometer system 4-mm ID Z 6-mm OD "\ 4. Apparatus (do not substitute) 4.1 Emission Spectrometry System (fig. 51) Tangential consisting of ——————— argon inlet 4.1.1 Spectrometer, Jarrel-Ash Plasma Atom Comp, 0.75-meter focal curve with —19/38 Vycor spectrum-shifter background correction and socket crossflow pneumatic nebulizer or Babington- type nebulizer as described by Garbarino and Taylor (1980). (See table 8 for element wavelengths.) 4.1.2 Computer, Digital Equipment Co., )-——18/9 Vycor PDP8e. ' ball joint i 4.1.3 Quartz Torch (fig. 52). Aerosol inlel 4.1.4 Radio Frequency Generator, Plasma- Figure 52.—Quartz torch Therm Inc., Model HFS-2000D, 27.1-MHz. 4.1.5 Peristaltic Pump, Gilson, Model HP4 4.2 Refer to the Jarrell-Ash Instruction Man­ (fig. 53). ual, Atom Comp 750, for operating techniques. METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 519 4.2.2 The software matrix containing all the required parameters for data acquisition is shown in table 9. Only three of these parameters ever require an update The background con­ Pneumatic stants should be updated wherever the plasma nebulizer torch position has been changed. Background constants are obtained by setting them equal Gilson to 1.000, except for Li-channel 24 and Na- pump Sample cup channel 23, by aspirating the blank solution, and then by making several measurements in inten­ sities. From these intensity measurements new 1 Technicon tubing SMA-p^ flow rate 0.42 mL/min background constants are calculated vising the part 116-0549PO8, collar color-orange formula: : (1A-4 inches, 1B-6 inches) 2 Teflon tubing 26TW NAT: 4 inches 3 Tube connector part 116-0003-0 4 Technicon tubing SMA™- flow rate 0.80 mL/min part 116-0549P10 collar color-red-standard Figure 53.—Pump system where B — new background constant, IN = net inten­ 4.2.1 sity and /g = background intensity. The new Operating conditions: background constants are then entered into the Incident RF power —- 1.25 kW matrix. Reflected RF power —— W When background constants are updated the Vertical observation posi­ interelement-correction factors must be up­ tion ————————— 16 mm (above dated. Interelement-correction factors are load coil) obtained by setting them equal to zero, stand­ Horizontal observation ardizing the instrument, analyzing each position ——————— Center interfering-element standard stock solution, and Argon head pressure — 40 lb/in.2 printing the results in concentration units. Sample argon pressure for These results are used to calculate the crossflow nebulizer — 17 lb/in.2 interelement-correction factors for each element Sample argon pressure for using the formula: Babington nebulizer - 30 lb/in.2 Sample argon flow rate for crossflow nebulizer — 0.9 L/min Sample argon flow rate for Babington nebulizer (approx) ——————— 0.6 L/min where Plasma argon flow rate Ie — interelement correction factor for element (for both nebulizers) - 0 L/min e, Ai = the apparent concentration of element Coolant argon flow rate 18 L/min e, and Q = concentration of the interfering ele­ Sample pumping rate for ment i. The units of Ie are milligrams per liter crossflow nebulizer — 10 percent of element e per milligrams per liter of interfer­ above ing element i. New interelement correction fac­ aspiration tors are then entered into the matrix. Sample pumping rate for Finally, in some cases it is impractical to make Babington nebulizer - 3 to 5 mL/min standard stock solutions at concentrations of Refractor plate position Optimized for exactly 100.0 mg/L. Therefore, the concentration Hg profile for each element should be entered Jinto the Spectrum shifter Full shift matrix. 520 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 5. Reagents 5.2.7 Iron standard solution 7, 1.00 mL = 5.1 Acids used in the preparation of stand­ 100 jig Fe: Dissolve 0.1000 g iron wire in a ards must be Ultrex grade or equivalent. minimum of dilute HNO3. Heat to increase rate 5.1.1 Aqua regia: Cautiously mix 3 parts con­ of dissolution. Add 10.0 mL concentrated HNO3 centrated HC1 (sp gr 1.19) and 1 part concen­ (sp gr 1.41) and dilute to 1,000 mL with demin­ trated HNO3 (sp gr 1.41) just before usa eralized water. 5.1.2 Hydrochloric acid, 6M: Add 500 mL 5.2.8 Lead standard solution 7, 1.00 mL = concentrated HC1 (sp gr 1.19) to 400 mL demin- 100 /4g Pb: Dissolve 0.1000 g lead shot in a eralized water and dilute to 1 L. minimum of dilute HNO3. Heat to increase rate 5.2 Prepare standard stock solutions from of dissolution. Add 10.0 mL concentrated HNO3 Spex HiPure-grade chemicals or equivalent. Dry (sp gr 1.41) and dilute to 1,000 mL with demin­ all salts for 1 h at 105 °C unless otherwise eralized water. specified. Do not dry hydrated salts. Clean all 5.2.9 Lithium standard solution 7, 1.00 metals thoroughly with the appropriate acid and mL = 100 jig Li Dissolve 0.5323 g I^COa* slow­ dry prior to weighing. ly, in a minimum amount of dilute HNO3. Add 5.2.1 Barium standard solution 7, 1.00 mL = 10.0 mL concentrated HNO3 (sp gr 1.41) and 100 Mg Ba: Dissolve 0.1516 g BaCl2 dried at dilute to 1,000 mL with demineralized water. 180 °C for 1 h in 10 mL demineralized water with 5.2.10 Magnesium standard solution 7, 1.00 1 mL 6M HCL Add 10.0 mL 6M HC1 and dilute mL = 100 Mg Mg: Dissolve 0.1000 g magnesium to 1,000 mL with demineralized water. rod in a minimum of dilute HNO3. Heat to in­ 5.2.2 Beryllium standard solution 7,1.00 mL = crease rate of dissolution. Add 10.0 mL concen­ 100 /ig Be: Dissolve 0.1000 g beryllium flakes— trated HNO3 (sp gr 1.41) and dilute to 1,000 mL CAUTION: deadly poison—in a minimum of aqua with demineralized water. regia Heat to increase rate of dissolution. Add 10.0 5.2.11 Manganese standard solution I, 1.00 mL concentrated HNO3 (sp gr 1.41) and dilute to mL = 100 fig Mn: Dissolve 0.1000 g manganese 1,000 mL with demineralized water (NOTE 1). flakes in a minimum of dilute HNO3. Heat to in­ NOTE 1. Beryllium is extremely toxic and may crease rate of dissolution. Add 10.0 mL concen­ be fatal if swallowed or inhaled. trated HNO3 (sp gr 1.41) and dilute to 1,000 mL 5.2.3 Calcium standard solution I, 1.00 with demineralized water. mL = 100 /ig Ca: Suspend 0.2498 g CaCO3 dried 5.2.12 Molybdenum standard solution 7, 1.00 at 180 °C for 1 h before weighing, in demineral­ mL = 100 Mg Mo: Dissolve 0.2043 g (NH4)2MoO4 ized water and dissolve cautiously with a in demineralized water. Dilute to 1,000 mL with minimum amount of dilute HNO3. Add 10.0 mL demineralized water. concentrated HNO3 (sp gr 1.41) and dilute to 5.2.13 Silica standard solution 7, 1.00 mL = 1,000 mL with demineralized water. 100 ^ SiO2: Dissolve 0.3531 g Na2SiO3-5H2O 5.2.4 Cadmium standard solution 7, 1.00 in demineralized water. Add 10.0 mL concen­ mL = 100 /*g Cd: Dissolve 0.1000 g cadmium trated HNO3 (sp gr 1.41) and dilute to 1,000 mL splatters in a minimum of dilute HNO3. Heat to with demineralized water. increase rate of dissolution. Add 10.0 mL concen­ 5.2.14 Sodium standard solution 7, 1.00 trated HNO3 (sp gr 1.41) and dilute to 1,000 mL mL = 500 Mg Na: Dissolve 1.271 g NaCl in de- with demineralized water. mineralized water. Add 10.0 mL concentrated 5.2.5 Cobalt standard solution 1, 1.00 mL = HNO3 (sp gr 1.41) and dilute to 1,000 mL with 100 jig Co: Dissolve 0.4939 g cobalt nitrate, demineralized water. Co(NO3)2-6H2O, in demineralized water. Add 10.0 5.2.15 Strontium standard solution I, 1.00 mL concentrated HNO3 (sp gr 1.41) and dilute mL = 100 /*g Sr: Dissolve 0.2416 g Sr(NO3)2 in to 1,000 mL with demineralized water. demineralized water. Add 10.0 mL concentrated 5.2.6 Copper standard solution 7,1.00 mL = HNO3 (sp gr 1.41) and dilute to 1,000 mL with 100 fig Cu: Dissolve 0.1000 g copper shot in a demineralized water. minimum of dilute HNO3. Heat to increase rate 5.2.16 Vanadium standard solution I, 1.00 of dissolution. Add 10.0 mL concentrated HNO3 mL = 100 fig V: Dissolve 0.2297 g NH4VO3 in (sp gr 1.41) and dilute to 1,000 mL with demin­ a minimum amount of concentrated HNO3. eralized water. Heat to increase rate of dissolution. Add 10.0 mL METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 521 concentrated HNO3 (sp gr 1.41) and dilute to command, and profile the instrument by averag­ 1,000 with demineralized water. ing the micrometer settings obtained at identical 5.2.17 Zinc standard solution /, 1.00 mL = intensity positions on each side of the mercury 100 /ig Zn: Dissolve 0.1000 g zinc powder in a spectral line Position the micrometer to the minimum of dilute HNO3. Heat to increase rate average setting. of dissolution. Add 10.0 mL of concentrated 6.4 Standardize the data system by running HNO3 (sp gr 1.41) and dilute to 1,000 mL with a blank and the series of four mixed standard demineralized water. solutions using an "O" command to initiate each 5.3 Mixed working-standard solutions. run. Identify the standard at the end of. each run 5.3.1 Prepare four mixed standard solutions as when demanded by the computer. Pump blank follows: Pipet 50.0 mL of each appropriate stand­ solution for 30 s between standards. AJlow 30 s ard stock solution into a 500-mL volumetric for equilibration each time a new solution is in­ flask. Dilute with demineralized water. Transfer troduced. to acid-rinsed PTFE bottle for storage Freshly 6.5 Change the "coded string" to the follow­ mixed standards should be prepared weekly. ing: (QEGGAC). Analyze the check standard Final concentration will be 1.00 mL — 10.0 /ig for described in paragraph 5.4. Concentration values all parameters exception sodium, which will be obtained should not deviate from the actual 1.00 mL = 50.0 /ig. Composition for mixed stand­ values by more than 2 percent. If values do ards should be as follows: deviate more than 2 percent, inspect nebulizer for 5.3.2 Mixed standard solution I: Iron, cad­ malfunction. mium, lead, and zinc. 6.6 Check standardization by running secon­ 5.3.3 Mixed standard solution II: Beryllium, dary reference samples or equivalent certified copper, strontium, vanadium, and cobalt. reference samples in natural matrix materials. 5.3.4 Mixed standard solution III: Molyb­ The determined concentration must be within denum, silica, lithium, and barium. one standard deviation of the elemental mean 5.3.5 Mixed standard solution IV: Calcium, given for the reference material magnesium, manganese, and sodium. 6.7 Analyze samples allowing 30 s for 5.3.6 Reagent blank: Dilute 1 mL concentra­ equilibration. Pump blank solution for 30 s be- tion HNO3 (sp gr 1.41) to 1,000 mL with demin­ tween samples. Check calibration after analyzing eralized water. 10 samples by rerunning a reference sstmple and 5.4 Check standard solution: Pipet 5.00 mL the check standard. The results for the reference of each standard stock solution into a 100-mL sample and check standard must be within volumetric flask. Dilute with demineralized one-standard-deviation of the elemental mean water. Transfer to PTFE bottle for storage Fresh given for the reference material and less than check standard solution should be prepared ± 2 percent for each element respectively. If not, weekly. Final concentration will be 1.00 mL = the data system must be restandardized as 5.00 /ig for all parameters except Na, which will described starting at paragraph 6.3. be 1.00 mL = 28.83 /ig (due to the Na in the 6.8 Reprofile instrument (paragraph 6.3) as SiO2 standard). necessary. If profile position changes by more than 4 micrometer units, the instrument must 6. Procedure be restandardized (starting with paragraph 6.2). 6.1 Set up instrument with proper operating parameters (paragraph 4.2) and ignite plasma In­ 7. Calculations strument must warm for 30 min prior to stand­ 7.1 All calculations are performed internally ardization. by the computer data system. SiO2 will! be label­ 6.2 Retrieve the appropriate proprietary soft­ ed Si if headings are used to identify the results. ware matrix from memory. Set the Time and 7.2 If dilutions were performed, multiply the Data Set number of cycles for spectrum shifter results by the appropriate dilution factor. to 5. Enter the following "coded string" for standardization: (QEGGAIN). 8. Report 6.3 Position the mercury pen lamp in front of 8.1 All results are printed directly in milli­ the entrance slit. Initiate the "profile" computer grams per liter (NOTE 2). 522 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Table 9.—Single-operator precision data for ICP 8.2.2 Beryllium (01010), cadmium (01025), Constituent Slope Intercept Units manganese (01056), and strontium (01080): less Barium 0.0061 0.83 M9/L than 10 jig/L, nearest figlL; 10 jtg/L and above, Beryllium .0061 .06 Do. two significant figures. Cadmium .0203 .30 Do. 8.2.3 Barium (01005), cobalt (01035), iron Cobalt .0650 .40 Do. Copper .0039 1.32 Do. (01046), lithium (01130), and zinc (01090): less Iron .0071 .059 Do. than 10 jig/L, nearest /tg/L to the lower limit of Lead .1210 5.0 Do. detection as specified in table 8; 10 /ig/L and Lithium .0240 .076 Do. Manganese .0042 .30 Do. above, two significant figures. Molybdenum .1220 .18 Do. 8.2.4 Copper (01040), lead (01049), molyb­ Strontium .0089 .076 Do. Zinc .0059 1.24 Do. denum (01060), and vanadium (01085): less than Calcium .0044 .30 mg/L 100 Mg/L, nearest 10 Mg/L; 100 iiglL and above, Magnesium .0060 .018 Do. two significant figures. Silica (Si02) .0040 .019 Do. Sodium .0077 .26 Do. 9. Precision Standard deviation, S0, is calculated by So = mx + />, where m is slope of line, x is concentration of constituent 9.1 Within its designated range, single- in units specified, and b is intercept. operator precision of the method for each metal may be expressed as described in table 9. A minimum of 10 replicate analystes were performed NOTE 2. If either the reported calcium or sodium to obtain each regression equation shown. concentration is greater than 100 mg/L or the 9.2 Interlaboratory precision data obtained magnesium concentration is greater than 5.0 on standard reference water samples are shown mg/L, report the second value given, otherwise in table 10. The specific instrument described in report only the first value. Ttace-metal results this method may not have tosen used. Labora­ must be converted to micrograms per liter. tories were not asked to provide this information. 8.2 Report the dissolved constituent concen­ trations as follows: Reference 8.2.1 Calcium (00915), magnesium (00925), Garbarino, J. R., and Ikylor, H. E., 1980, A Babington-type silica (00955), and sodium (00930): less than 10 nebulizer for use in the analysis of natural water samples mg/L, one decimal; 10 mg/L and above, two by inductively coupled plasma ftpectrometry: Applied significant figures. Spectroscopy, v. 34, p. 584-90.

Table 10.—Interlaboratory precision data for ICP [ST = overall precision, In units specified and X= concentration of constituent, tn units specified; SCU = average standard deviation, In units specified and Cl = 95 percent confidence Intervals for the average standard deviation, In units specified.)

Number of Range fog/L Correlation Constituent samples except where noted) Precision coefficient Barium 6 18 to 240 Sr = 0.055 X+ 168 0.9448 Beryllium 6 4.0 to 47 Sr = 0.056 X+ 0.836 .8442 Cadmium 6 4.0 to 15 Sr = 0.396 X -1.50 .8992 Calcium 7 .77 to 186 mg/L S7 = 0.067 X -0.433 .9907 Cobalt 6 3.5 to 14 SDp = 3.3 — C/ = 2.6 to 4.6 Copper 6 22 to 470 Sr = 0.065 X+ 2.97 .9915 Iron 7 100 to 770 SDp = 24.1 C/ = 20.1 to 29.8 Lithium 6 43 to 650 Sf = 0.092 X+ 3.59 .8337 Magnesium 7 .10 to 120 mg/L Sr = 0.044 X+ 0.072 .9985 Manganese 6 38 to 570 SDp = 23.1 — C/ = 18.8 to 28.5 Molybdenum 5 12 to 36 SDp = 5.7 — C/ = 4.5 to 8.1 Silica (SiO2) 5 5.2 to 11 mg/L SDp = 0.78 — C/ = 0.62 to 1.06 Sodium 7 .33 to 160 mg/L Sr = 0.027 X+ 0.763 .9215 Strontium 12 57 to 2700 ST = 0.042 X+ 3.73 .9345 Vanadium 5 6.0 to 10 Sr = 0.879 X -4.72 .9557 Zinc 6 15 to 570 SDp = 14.0 — C/ a 11.6 to 17.8 Anions, ion-exchange chromatographic, automated

Parameters and Codes: Anions, dissolved, 1-2057-85 (see below)

Parameter Code Parameter I Code Bromide (mg/L as Br) 71870 Nitrite (mg/L as N) 00613 Chloride (mg/L as Cl) 00940 Orthophosphate (mg/L as P) 00671 Fluoride (mg/L as F) 00950 Sulfate (mg/L as SO4) 00945 Nitrate (mg/L as N) 00618

1. Application Table 11.—Working ranges of anions by ion 1.1 This method may be used only for the ; chromatography determination of dissolved bromide, chloride, Minimum Maximum fluoride, nitrate, nitrite, orthophosphate, and concentration1 concentration sulfate in natural water. Table 11 shows approx­ Constituent (mg/L) (mg/L) Fluoride 0.01 50 imate lower and upper concentration limits. Ac­ Chloride .20 50 tual limits depend on many factors including Nitrite-nitrogen .02 70 the column age, which affects column resolu­ Orthophosphate-phosphorus .06 40 Bromide .10 150 tion, the relative concentrations of closely Nitrate-Nitrogen .05 150 eluting species, and the volume of the sample Suifate : .20 100 injected. Samples containing anion concentra­ 1Wtth a larger sample loop (for example, 600 /iL), minimum concentra­ tions high enough to overload the column resins tion levels can be lowered. or interfere with closely eluting species need to be diluted or a sample loop smaller than the 20O/iL sample loop specified in this method that 1C technology is rapidly changing and needs to be used. Sample dilution or use of developing. smaller volumes will change the detection limits for all anions. 2. Summary of method 1.2 Analyses must be performed on filtered 2.1 A sample is injected into an ion and unacidified samples. chromatograph and is pumped through three 1.3 The ion chromatographic (1C) technol­ different ion-exchange columns into a specific- ogy is so new that instruments and associated conductivity detector. The first two columns, data-processing equipment and software a precolumn and separator column, are packed available on the commercial market are not with low-capacity anion exchanger. Ions are standardized and operating conditions vary separated based on their affinity tor the ex­ enormously. Until operating conditions of change sites of the resin. The last column is a various manufacturers' instruments become suppressor column that contains cation- more comparable and the equivalency of exchange resin in the hydrogen form, The sup­ methods using those instruments is established pressor column reduces the background conduc­ by extensive testing, the 1C method approved tivity of the eluent to a low or negligible level for U.S. Geological Survey use will specify and converts the anions in the sample into their instrument and associated software brands. corresponding acids. The separated anions in This does not imply endorsement of one prod­ their acid form are measured using an electrical- uct over another, but rather, acknowledges conductivity cell. Anions are identified based 523 524 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS on their retention times compared with known to prepare a blank using demineralized water at standards. Quantitation is accomplished by eluent strength in bicarbonate and carbonate to measuring the peak height or area and by com­ indicate any interferences that may have been in­ paring it with an analytical curve generated from troduced by the sample-preparation technique known standards. 3.4 Samples containing high concentrations 2.2 During analysis, the suppressor column of chloride or other anions may prevent resolu­ will slowly be exhausted and, therefore, will need tion of closely eluting peaks. For example, the to be regenerated. Other suppressors, such as the peak for 0.1 mg of bromide per liter in the hollow-fiber suppressor, which is continuously presence of greater than 1,000 mg of chloride per regenerated, may be used. liter is swamped by the chloride peak Bromide 2.3 For additional information on ion begins to elute before the chloride peak complete­ chromatography, see Small and others (1975) and ly returns to the baseline Fishman and Pyen (1979). 3.5 Unexpected, late-eluting peaks are a potential source of interference A peak eluting 3. Interferences about two minutes after sulfate, believed to be 3.1 Because bromide and nitrate elute very oxalate, has been observed in some precipitation closely together, they potentially interfere with samples. each other. Bromide-to-nitrate ratios should not exceed 1:10 or 10:1 if both ions are to be quan- 4 Apparatus titated 4.1 Ion Chromatography Dionex Model 12; 3.2 High levels of organic acids may be pres­ auto-sampler, Gilson; integrator (NOTE 1), Spec­ ent in industrial and domestic wastes which may tra Physics using the following operating con­ interfere with inorganic-anion analysis. TWo com­ ditions: mon species, formate and acetate, elute between Sample loop ————— 200 jiL fluoride and chlorida Eluent flow rate ——— 138 mL/h (30 3.3 Water from the sample injection will percent of full cause a negative peak or dip in the chromato- capacity) gram when it elutes, because its conductivity is Sample pump flow rate 50 percent of less than that of the suppressed eluent. This dip full capacity usually occurs between F-1 and Cl'1. Any peak Specific conductance of interest eluting near the water dip must be suf­ meter settings —— 10, 30, or 100 j*S ficiently resolved from the dip to be accurately NOTE 1. A dual pen recorder (1 V and 100 mV) quantitated A method of eliminating the con­ may replace an integrator. The recorder should ductivity drop due to bicarbonate and carbonate be capable of full-scale response in two seconds is to introduce into the sample concentrations of or less. A typical chart speed is 0.5 cm/min. bicarbonate and carbonate that closely approx­ 4.1.1 Precolumn, 4 X 50-mm, fast-run, anion- imate those of the eluent used for analysis. Ad­ resin column (Dionex HN 030831 or equivalent) justment of the sample background may be placed before the separator cokimn to protect the accomplished in two ways. separator column from contamination by par- 3.3.1 Dilute the sample with eluent if sample ticulates or species strongly retained by the ion- dilution is required prior to analysis. exchange resin. 3.3.2 A volume of 1.0 mL of a prepared eluent 4.1.2 Separator column, 4 X 250-mm, fast- concentrate (a solution that is 100 times more run, anion-separator column packed with low- concentrated than the eluent with respect to capacity, pellicular, anion-exchange resin (Dionex bicarbonate and carbonate ions) can be added per FN 030830 or equivalent) that is styrene 100.0 mL of sample CAUTION:.Samples pre­ divinylbenzene-based. This is suitable for resolv­ pared in this manner have a pH of about 10 and ing fluoride, chloride, nitrite, orthophosphate, will readily absorb carbon dioxide if left exposed bromide, nitrate, and sulfate to the atmosphere. The result will cause a 4.1.3 Suppressor column^ 6 X 250-mm, positive-peak interference column-packed, with a high-capacity, column- ex­ 3.3.3 Standard solutions need to be prepared in change resin (Dowex 50W-X 16-H form resin or the same manner as the samples. It is important equivalent) that is capable of converting the METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 525

Concentration Volume eluent and separated anions to their respective Anion (mL) acid forms. F 5.00 5 4.2 For additional information, refer to the Cl 50.0 50 different manufacturers' instruction manuals. NO2-N 5.0 5 PO4-P 5.0 55 5. Reagents Br 5.0 5 soNOq'N43 50.0 50 5.1 Eluent, 0.003 M sodium bicarbonate- 50.0 50 0.0024 M sodium carbonate: Dissolve 0.2520 g NaHCO3 and 0.2544 g Na^Og in demoralized water and dilute to 1 L (NOTE 2). NOTE 3. If nitrite is omitted from the mixed NOTE 2: Eluent concentration may be varied stock solution, the solution is stable for at least slightly to obtain the same retention times for 1 month when stored and refrigerated in a dean each anion when a new separator column is used. TFE-fluorocarbon bottle If nitrite is included in The NaHCO3 is subject to thermal decomposi­ the mixed-stock solution, the solution needs to tion and must be weighed without prior drying. be prepared fresh daily. 5.2 Suppressor regeneration solution, IN NOTE 4. The above is only an example of a H2SO4: Cautiously add 111 mL concentrated mixed-stock solution. Other appropriate concen­ H2SO4 (sp gr 1.84) to approx 600 mL deminer­ trations can be prepared. alized water. Cool and dilute to 4 L with demin- 5.5 Mixed standard solutions: Prepare at eralized water. least three mixed standard solutions by ap­ 5.3 Standard anion solutions: Dry all salts propriate dilution of the mixed stock solution. for 1 h at 105 °C unless otherwise specified. The solutions should bracket the concentration Store each standard solution in TFE-fluor- range of interest. ocarbon bottles. 5.3.1 Bromide standard solution, 1.00 mL = 6. Procedure 1.00 mg Br: Dissolve 1.2877 g NaBr in demin- 6.1 Set up the ion chromatograph according eralized water and dilute to 1,000 mL. to the operating parameters described in 4.1. 5.3.2 Chloride standard solution, 1.00 mL = Equilibrate i the columns with eluent until a 1.00 mg Cl: Dissolve 1.6484 g NaCl in deminer* stable baseline is obtained. Allow approximate­ alized water and dilute to 1,000 mL. ly 30 min for equilibration. 5.3.3 Fluoride standard solution, 1.00 mL = 6.2 Set the full-scale conductivity ito 10, 30, 1.00 mg F: Dissolve 2.2101 g NaF in deminer- or 100 pS as is appropriate for the expected alized water and dilute to 1,000 mL. sample-anion concentrations. The higher settings 5.3.4 Nitrate-nitrogen standard solution, 1.00 are required for higher sample-anion concen­ mL = 1.00 mg NO3-N: Dissolve 6.0681 g trations. NaNO3 in demineralized water and dilute to 6.3 Level the integrator at 10 mV (a display 1,000 mL. of 1000 with no signal). Adjust the ion 5.3.5 Nitrite-nitrogen standard solution, 1.00 chromatograph's offset to approximately 11 mV mL = 1.00 mg NO2-N: Dissolve 4.9259 g (a display of 1100). This ensures that the ion NaNO2 in demineralized water and dilute to chromatograph's signal will not fall below 10 mV 1,000 mL. during the course of the analyses. The baseline 5.3.6 Phosphorus standard solution, 1.00 signal tends to drift in a negative direction over mL = 1.00 mg P: Dissolve 4.3936 g anhydrous a long period of time Each chromato^am can KH2PO4 in demineralized water and dilute to be started at a signal level of 10 mV using the 1,000 mL. integrator's automatic-zero control 5.3.7 Sulfate standard solution, 1.00 mL = 6.4 Enter an appropriate program into the 1.00 mg SO4: Dissolve 1.8140 g K2SO4 in de- main program controller of the ion chromato­ mineralized water and dilute to 1,000 mL. graph according to the manufacturer's instruc­ 5.4 Mixed stock solution: Prepare 1,000 mL tion manual The system is configured so that mixed stock solution by appropriate quan­ the ion chromatograph controls the autosampler titative dilution of each standard solution and starts the integrator at the beginning of each (NOTES 3 and 4). sample injection (NOTE 5). 526 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS NOTE 5. For additional information on compu­ Table 12.—Approximate retention times of anions by ion terized data reduction, see Hedley and Fishman chromatography Time (1982). Constituent (min) 6.5 Place the mixed standard solutions in the Fluoride 2.2 first positions of the sample tray followed by a Chloride 3.3 standard reference material and then the sam­ Nitrate-nitrogen 4.0 ples. Place a standard reference material in every Orthophosphate-phosphorus 4.9 Bromide 6.5 twentieth position of the remainder of the sam­ Nitrate-nitrogen 7.5 ple tray. Sulfate 8.6 6.6 Create an information file in the in­ tegrator by pressing the DIALOG key. Through this information file, various integrator functions Table 13.—Precision for ion chromatographic determination can be enabled or disabled during the recording of anions of a chromatograrrt The only necessary function Relative Standard standard is ER (end run). It terminates the chromatogram Mean deviation deviation at the appropriate time as determined by the Constituent (mg/L) (mg/L) (percent) operator's setting of the ion chromatograph's Bromide 0.295 0.020 6.8 controller, which actuates the sampler and causes Chloride .72 .04 5.6 the injection of a new sampla Da 1.71 .06 3.5 Da 2.72 .24 8.8 6.7 Press the integrator's PT EVAL key be­ Da 5.84 .19 3.2 fore starting a series of analyses. The integrator Da 9.90 .39 3.9 will take about 50 s to store the baseline signal Da 58.6 .7 1.2 Do. 119 1.2 1.0 so that a peak can be distinguished from baseline Fluoride .018 .004 22.2 noise The baseline noise can be evaluated before Do .080 .010 12.5 each chromatogram, using the integrator's ET Do .79 .02 2.5 function. Do .92 .01 1.1 Da 2.02 .15 7.4 6.8 Set the ion chromatograph's PGMAUTCV Nitrate-nitrogen .12 .01 8.3 MANUAL switch from MANUAL to AUTO and Do .42 .051 19 press Start/Step to begin the analyses. Do .70 .081 1.4 Da 1.27 .05 3.9 Da 5.26 .14 2.7 7. Calculation Nitrite-nitrogen .03 .01 33.3 7.1 The integrator automatically computes Orthophosphate-phosphorus .273 .010 3.7 Sulfate 1.68 .05 3.0 the concentration of each anion in each sample Da 3.88 .10 2.6 by comparing its peak height or area to the Da 15.1 .80 5.3 analytical curve. Retention times for the seven Da 62.1 .9 1.4 Da 100 1.4 1.4 anions are given in table 12. Da 146 3 2.0 8. Report 8.1 Report bromide (71870), chloride (00940), fluoride (00950), nitrate-nitrogen (00618), nitrite- References nitrogen (00613), orthophosphate-phosphorus Fishman, M. J., and Pyen, G. a, 1979, Determination of (00660), and sulfate (00945), dissolved, concentra­ selected anions in water by ion chromatography: U.S. tions as follows: less than 1 mg/L, nearest 0.01 Geological Survey Water-Resources Investigations, mg/L; 1 mg/L and above, two significant figures. 79-101. 30 PL Hedley. A> G., and Fishman, M. J., 1982, Automation of an 9. Precision ion chromatograph for precipitation analysis with com­ puterized data reduction: U.S. Geological Survey Water- 9.1 Analysis of a number of test samples 10 Resources Investigations, 81-78, 33 p. times each by one operator resulted in mean Small, H., Stevens, T. S., Bauman, W. G, 1975, Novel ion ex­ values, standard deviations, and percent relative change chromatographic method using conductimetric standard deviations as shown in table 13. detection: Analytical Chemistry, v. 47, p. 1801-9. Anions, ion-exchange chromatographic, low ionic-strength water, automated

Parameters and Codes: Anions, dissolved, 1-2058-85 (see below)

Parameter Code Parameter Code Bromide (mg/L as Br) 71870 Nitrate (mg/L as N) 00618 Chloride (mg/L as Cl) 00940 Orthophosphate (mg/L as P) 00671 Fluoride (mg/L as F) 00950 Sulfate (mg/L as SOJ 00945

1. Application Table 14.—Analytical ranges used in the determination 1.1 This method may be used only for the of the six anions determination of dissolved bromide, chloride, Minimum Maximum concenration concentration fluoride, nitrate, Orthophosphate, and sulfate in Constituent (mg/L) (mfl/L) water with a specific conductance of approx 100 Fluoride 0.01 0.5 fiSlcm or less. Table 14 specifies the lower and Chloride .01 3.0 upper concentration limits using a 200-/xL sam­ Orthophosphate-phosphorus .01 .6 ple loop. Samples containing anion concentra­ Bromide .01 .6 Nitrate-nitrogen .01 .6 tions greater than the upper concentration Sulfate ! .01 10.0 limits must be diluted or the conductivity meter must be changed to a less sensitive setting before analysis. through the suppressor's interior. Tltis latter 1.2 Analyses must be performed on a process operates continuously. filtered (rinsed 0.45-jun membrane filter) or 2.3 For additional information on ion chrom- particulate-free, unacidified sample. atography, see Small and others (1915).

2. Summary of method 3. Interferences 2.1 All six anions are determined on a single 3.1 A negative peak or dip, which is caused filtered or particulate-free, unacidified sample by a combination of water and carbonate, is with an ion chromatograph. seen in the chromatogram using a fiber sup­ 2.2 In anion analysis, the ions of interest pressor. This interference is eliminated by elute through an anion-ion exchange separator adding concentrated eluent to the sample. column at different rates, depending upon the 3.2 Because low ionic-strength samples con­ affinity of each anion for the ion- exchange resin. tain low concentrations of these sis: anions, Then the ions elute through a fiber suppressor, there will be no unresolved peaks and, therefore, which consists of a semi-permeable membrane no interferences. in the interior of the suppressor's outer shell. 3.3 Oxalate, acetate, or formate may in­ The membrane is wrapped around the interior terfere if present. of the fiber, which is packed with inert beads. A suppressor regenerant solution flows counter- 4. Apparatus current to the eluent intrained samples and sur­ 4.1 Ion Chromatograph, Dionex Model 212Oi rounds the outside of the semi-permeable fiber. (NOTE 1) or equivalent, using the following The regenerant is continuously fed by gravity operating conditions: 527 528 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Eluent-pump flow rate 2.0 mL/min Anion Salt 9/L Sample loop ————— 200 /iL Br NaBr 1.2877 Specific-conductance Cl NaCl 1.6484 F NaF 2.2101 meter settings —— 1,3,10,30 p,S N03-N NaNO« 6.0681 NOTE 1. Concentration limits and operating PO,-Pso4 4.3936 conditions may vary according to model of in­ 1.8140 strument. 4.2 Pump, LDC/Milton Roy miniMetric I 5.2 Anion Stock Solutions II, 1.00 mL = (NOTE 2) or equivalent that gives pulse-free 0.10 mg: Prepare chloride and sulfate stock solu­ flow of liquid. These pumps are used to tions by diluting 100 mL each of chloride and eliminate "water and carbonate dip" by adding sulfate stock solutions I to 1,000 mL with de- a volume of concentrated eluent (lOx) to each mineralized water and store in Teflon bottles. sample. 5.3 Concentrated eluent, 0.0280M sodium bicarbonate-0.0225M sodium carbonate: Sample pump flow rate 2.4 mL/min Concentrated eluent Dissolve 9.408 g NaHCO3 and 9.540 g NagCOg in demineralized water and dilute to 4 L. pump flow rate —— 0.23 mL/min 5.4 Demineralized water: Pass water (NOTE 3) through a post column (millipore or equivalent) NOTE 2. Deactivate the Reset switch to bypass with 0.2-/un pore size filter which is placed after the low-pressure-limit adjustment. laboratory demineralized water system. NOTE 3. These flow rates will vary slightly 5.5 Eluent, 0.00280M sodium bicarbo- depending on the eluent concentration. Adjust nate-0.00225Af sodium carbonate (NOTE 4): flow rates of pumps by injecting a blank until Dissolve 5.410 g NaHCO3 and 5.486 g NagCOg "water and carbonate dip" disappears. in demineralized water and diulute to 23 L. 4.2.1 Sample and concentrated eluent NOTE 4. Eluent concentration may be varied pumps are connected to the ion chromato- slightly to obtain the same retention times for graphic Relays 3 and 4, respectively, and are each anion when a new separator column is controlled by Auto Ion 100 Controller program. used. 4.3 Integrator, Spectra Physics; auto 5.6 Mixed-anion standard solution I: Pre­ sampler, Gilson or their equivalents, connected pare 1,000 mL by appropriate quantitative dilu­ to the ion chromatograph's Relays 1 and 2, tion of anion stock solutions I with deminer­ respectively. alized water. 4.4 Proportioning pump, Technicon, or equivalent, provides demineralized water into Concentration Volume Anion (mg/L) (m/L) the wash receptacle of the sampler. 4.5 Precolumn, HPIC AS-4 Dionex pellicular Br 10 10.0 Cl 250 250 anion-resin or equivalent. F 10 10.0 4.6 Separator column, HPIC AS-4 Dionex N03-N 30 30.0 pellicular anion-resin or equivalent. PO.-P 10 10.0 so4 300 300 4.7 Suppressor, Dionex anion fiber sup­ pressor, No. 35350. 4.8 For additional information, refer to the 5.7 Mixed-anion standard solution II: Dilute manufacturers' instruction manuals. 10.0 mL mixed anion standard solution I to 1,000 mL with demineralized water.

5. Reagents Concentration 5.1 Anion stock solutions I, 1.00 mL = 1.00 Anion (mg/L) mg: Prepare six individual anion stock solutions Br 0.1 I by dissolving indicated amount of reagent- Cl 2.5 grade chemicals, dried to a constant weight at F .1 N03-N .3 105 °C, in demineralized water and dilute to PO.-P .1 1,000 mL and store in Teflon bottles. 3.0 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 529 5.8 Mixed-anion standard solution III: 6.6 Place mixed-anion standard solutions Prepare 1,000 mL by appropriate dilution of III and II at the beginning of the sample holder anion stock solutions II. followed by standard reference materials and samples. Place a standard reference material in Concentration Volume every tenth position of the remainder of this Anlon (mg/L) (mL) sample holder. Cl 0.2 2.0 S04 0.2 2.0 6.7 Turn on the proportioning pump to deliver demineralized water into the wash 5.9 Suppressor-regeneration solution, receptacle of the sampler. 0.025AT H2SO4: Cautiously add 2.8 mL concen­ 6.8 Press START on the OPERATION- trated H2SO4 (sp gr 1.84) to demineralized SELECT of Autolon 100 Controller to begin the water, cool, and dilute to 4L with demineralized analysis. water.

6. Procedure 7. Calculations 6.1 Operate instrument according to param­ 7.1 The integrator automatically computes eters described in paragraph 4.1. Supply con­ the concentrations of six anions in each sample tinuously by gravity-feeding suppressor- by comparing their peak heights to the regeneration solution for fiber supressor analytical curve. Approximate retention times (0.025AT H2SO4) at a flow rate of 2.4 mL/min. for the six anions are given in table 15. Equilibrate the columns with 0.00280M NaHCO3-0.00225M Na2CO3 eluent until base­ line stabilizes. Allow approximately 30 min for 8. Report equilibration. 8.1 Report bromide (71870), chloride (00940), 6.2 Enter appropriate program into the fluoride (00950), nitrate-nitrogen (00618), Auto Ion 100 Controller of ion chromatograph according to manufacturer's instructions. This orthophosphate-phosphorus (00660), and sulfate controls autosampler, integrator, sample pump, (00945), dissolved, concentrations as follows: and concentrated-eluent pump. This program is less than 1 mg/L, nearest 0.01 mg/L; 1.0 mg/L best suited for most of the precipitation and above, nearest 0.1 mg/L. samples. Set the OutPut Range of the conduc­ tivity meter similar to the expected concentra­ tion of samples. 9. Precision and Bias 6.3 Press the PT EVAL (peak threshold 9.1 Analysis of a number of test samples 10 evaluation) key for integrator to evaluate the times each by one operator resulted in mean detector signal for noise and drift. values, standard deviations, and percent 6.4 Create the information file through a relative standard deviations as shown in "dialog" with the integrator. table 16. Select calculation of the best straight-line fit using method 5 (external standard method) (NOTE 5). NOTE 5. For additional information on com­ Table 15.—Approximate retention times of anions Ttme puterized data reduction, see Hedley and Constituent (min) Fishman (1982). Fluoride 1.4 6.5 Run a demineralized water blank Chloride 2.2 through the system to ensure that flow rates Orthophosphate-phosphorus 3.4 of sample and concentrated-eluent pumps are Bromide 4.8 in correct proportion to eliminate the "water Nitrate-nitrogen 5.6 and carbonate dip." Sulfate ; 7.6 530 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS Table 16.—Precision and bias for ion chromatography on simulated precipitation samples

Intel-laboratory standard Ion chromatography data1 reference water Standard sample data reference water Relative sample Mean Standard standard Standard Constituent deviation Mean number (mg/L) deviation (mg/L) deviation2 (mg/L) (percent) (mg/L)

70 (1:10) F 0.09 0.01 8.1 0.089 0.06 Ct .23 .01 4.3 .271 .84 NOVN .06 .005 7.7 .069 .065 S0Qn 4 2.60 .07 2.6 2.62 1.4 72 (1:10) .10 .01 9.3 .09 0.06 Ct 4.89 .14 2.8 4.50 1.4 PO4-P .05 .004 8.8 .059 .048 N03-N .30 .01 4.4 .302 .29 S04 10.6 .34 3.2 11.1 10 P-1 Cl .40 .01 2.3 .44 .045 N03-N .13 .003 2.3 .12 .016 so. 1.14 .03 2.5 1.18 .09 P-2 .10 .01 7.8 .10 .00 Cl .47 .01 1.8 .60 .33 N03-N .04 .002 6.0 .074 .068 S0Of)4 2.96 .06 1.9 3.24 1.43 80 (1:10) .11 .01 9.4 .114 .07 Cl 3.20 .09 3.0 3.15 1.5 PO4-P .06 .005 9.6 .073 .063 N03-N .06 .004 7.3 .055 .070 S04 7.08 .16 2.3 7.24 5.15 1 Values based on 10 replicate determinations of SRWS. 2Standard deviations for undiluted SRWS.

References Small, H., Stevens, T. S., Bauman, W. C., 1975, Novel ion exchange chromatographic method using conduc- Fishman, M. J., and Pyen, G. S., 1979, Determination of timetric detection: Analytical Chemistry, v. 47, p. selected anions in water by ion chromatography: U.S. 1801-9. Geological Survey Water-Resources Investigations, 79-101, 30 p. Hedley, A. G., and Fishman, M. J., 1982, Automation of an Stevens, T. S., Davis J. C., and Small, H., 1981, Hollow fiber ion chromatograph for precipitation analysis with com­ ion-exchange suppressor for ion chromatography: puterized data reduction: U.S. Geological Survey Water- Analytical Chemistry, v. 53, p. 1488-92. Resources Investigations, 81-78, 33 p. Metals, major, total-in-sediment, atomic absorption spectrometric, direct

Parameters and Codes: Metals, total, (1-5473-85): none assigned Aluminum (mg/kg as Al) Calcium (mg/kg as Ca) Iron (mg/kg as Fe) \ Magnesium (mg/kg as Mg) | Manganese (mg/kg as Mn) Potassium (mg/kg as K) Silica (mg/kg as Si) Sodium (mg/kg as Na)

1. Application metaborate and lithium tetraborate in a 1.1 This method may be used to analyze graphite crucible in a muffle furnace at 1,000 °C. suspended and bottom sediment for the deter­ The resulting bead is dissolved in acidified, boil­ mination of total concentrations of the consti­ ing, demineralized water. The resulting solu­ tuents. The upper- and lower-concentration- tions are analyzed by atomic absorption reporting limits are specified below. Samples spectrometry after the addition of appropriate containing analyte concentrations greater than matrix modifiers. Additional interferences are the upper limit may be analyzed after ap­ removed or compensated for by the use of propriate dilution. mixed-salt standards. 2.2 Additional information on the principles Lower limit Upper limit of the method may be found in Shapiro (1975), Constituent (mg/kg) Johnson and Maxwell (1981), and Pinta (1982). Aluminum 20,000 150,000 Calcium 1,000 50,000 Iron 5,000 100,000 3. Interferences Magnesium 1,000 20,000 3.1 Both positive and negative, interelement Manganese 100 4,000 interferences occur and have been documented Potassium 1,000 35,000 Silica 40,000 150,000 (Johnson and Maxwell, 1981; Pinta, 1982). Sodium 1,000 25,000 3.2 Interferences are eliminated and (or) compensated for by use of cesium chloride (CsCl), orthoboric acid (H3BO3), lithium 1.2 Analyses must be performed on dried metaborate (LiBO2), lithium tetraborate and ground samples that have been fused with (Li2B4O7), and by the use of mixed-salt a lithium metaborate-lithium tetraborate flux, standards. > with the resulting bead dissolved in acidified, deionized water. These solutions are then 4. Apparatus analyzed by atomic absorption spectrometry. 4.1 Atomic absorption spectrometer equipped with electronic digital readout, 2. Summary of method automatic zero and concentration controls, and 2.1 A sediment sample is dried, ground, and an autosampler (optional). homogenized. The dried, ground, and homogen­ 4.2 Refer to the manufacturer's manual to ized sample is fused with a mixture of lithium optimize the instrument for the following: 531 532 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Grating: ultraviolet Burner: Oxldant: (uv) nitrous nitrous or visible Wavelength oxide (N50) oxide (N«O) Flame Constituent

4.3 Fuel, acetylene. 5.6 Working standard solutions 1, 2, and 3: 4.4 Graphite crucibles, drill-point, 7.5-mL Pipet 10 mL (standard 1), 6 mL (standard 2), capacity, 1-in. OD, %-in. ID, and 1 8/s-in. total and 2 mL (standard 3) mixed-salt standard solu­ depth. tions (5.5) into 100 mL volumetric flasks, and 4.5 Hollow-cathode lamps, single-element dilute each to 100 mL with standard diluent lamps. solution (5.10). Concentrations are as follows: 4.6 Magnetic stirrer. 4.7 Muffle furnace, capable of reaching a Standard 1 Standard 2 Standard 3 temperature of at least 1000 °C. Constituent (mp/L) (mg/L)

Sample 1 Sample 2 Relative Relative Number standard Number standard of Mean deviation of Mean deviation Constituent replicates (percent) (percent) replicates (percent) (percent) Aluminum 5 3.5 3 10 8.5 1 Calcium 5 .7 11 10 7.8 3 Iron 5 1.2 3 10 9.3 1 Magnesium 10 .5 2 5 4.3 3 Manganese 10 .02 20 5 .16 12 Potassium 10 .5 10 10 3.7 3 Silica 5 13.2 2 10 32.4 1 Sodium 5 .7 9 10 3.1 3

References Pints, M., 1982, Modern methods for trace element analysis, translated by STS Inc., Ann Arbor, Ann Arbor Science Publishers, 492 p. Johnson. W. M.t and Maxwell, J. A., 1981. Rock and min­ Shapiro, L., 1975. Rapid analysis of silicate, carbonate, and eral analysis, 2d ed.: New York, John Wiley & Sons, phosphate rocks: US. Geological Survey Bulletin 1401, 489 p. 76 p. Metals, major and minor, total -in-sediment, atomic absorption spectrometric direct

Parameters and Codes: Metals, total, (1-5474-85): none assigned Aluminum (mg/kg as Al) Cadmium (mg/kg as Cd) Calcium (mg/kg as Ca) Chromium (mg/kg as Cr) Cobalt (mg/kg as Co) Copper (mg/kg as Cu) ! Iron (mg/kg as Fe) ' Lead (mg/kg as Pb) Lithium (mg/kg as L!) i Magnesium (mg/kg as Mg) i Manganese (mg/kg as Mn) Nickel (mg/kg as Ni) Potassium (mg/kg as K) Sodium (mg/kg as Na) ! Strontium (mg/kg as Sr) Titanium (mg/kg as Ti) Zinc (mg/kg as Zn) ;

1. Application 1.2 Analyses must be performed on dried and 1.1 This method may be used to analyze ground samples that have been solubilized with suspended and bottom sediment for the determi­ a combination of nitric, hydrofluoric, and per­ nation of total concentration of the constituents. chloric acids heated in open Teflon beakers. The upper- and lower-concentration reporting These solutions are then analyzed by atomic ab­ limits are specified below. Samples containing sorption spectrometry. analyte concentrations greater than the upper limit may be analyzed after appropriate dilution. 2. Summary of method 2.1 A sediment sample is dried, ground, and Lower limit Upper limit homogenized. The dried, ground, and homogen­ Constituent (mg/kg) (mg/kg) ized sample is digested with a combination of Aluminum 20,000 150,000 nitric, hydrofluoric, and perchloric fields in a Cadmium .5 100 Calcium 1,000 50,000 Teflon beaker heated on a hotplate at 200 °C. The Chromium 3 400 resulting salts are dissolved in hydrocliloric acid Cobalt 3 600 and demineralized water. The resulting; solutions Copper 1 400 Iron 5,000 100,000 are analyzed by atomic absorption spectrometry Lead 3 1,000 after the addition, in certain cases, of appro­ Lithium 2 200 priate matrix modifiers. Additional interferences Magnesium 1,000 20,000 Manganese 100 4,000 are removed or compensated for through the Nickel 3 600 use of mixed-salt standards and background Potassium 1,000 35,000 Sodium 1,000 25,000 correction. Strontium 2.5 500 2.2 Additional information on the principles Titanium 1,000 20,000 of the method may be found in Walsh (1977), Zinc 1 160 Johnson and Maxwell (1981), and Piiita (1982).

535 536 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 3. Interferences 4. Apparatus 3.1 Both positive and negative interelement 4.1 Atomic absorption spectrometer interferences occur and have been documented equipped with electronic digital readout, (Walsh, 1977; Johnson and Maxwell, 1981; automatic zero and concentration controls, a Knta, 1982). deuterium-source background corrector, and an 3.2 Interferences are eliminated or compen­ autosampler (optional). sated for by the use of cesium chloride (CsCl), 4.2 Refer to the manufacturer's manual to the use of mixed-salt standards, and the use of optimize the instrument for the following: a deuterium-source background corrector.

Grating: ultraviolet Burner: Oxidant:

4.3 Beakers, Teflon, 100-mL capacity, thick- 5.3 Hydrochloric acid, concentrated (sp gr wall, capable of withstanding temperatures up 1.19). to 260 °C. 5.4 Hydrochloric acid, dilute (1 + 1): Add 4.4 Fuel, acetylene. 250 mL concentrated HC1 (sp gr 1.19) to 250 mL 4.5 Hollow-cathode lamps, single-element demineralized water. Store in a plastic bottle. lamps. 5.5 Hydrochloric acid, diluted + 49): Add 4.6 Hot plate, electric or gas, capable of 10 mL concentrated HC1 (sp gr 1.19) to 490 mL reaching at least 250 °C. demineralized water. Store in a plastic bottle. 4.7 Perchloric acid hood, with appropriate 5.6 Hydrofluoric acid, concentrated, 48- to washdown facility and gas or electric outlets. 51-percent, (sp gr 1.17). 5.7 Iron standard solution, 1.00 mL = 1.00 5. Reagents mg Fe: Dissolve 1.000 g Fe wire in 20 mL HC1 5.1 Aluminum standard solution, 1.00 mL = (1 + 1) and dilute to 1000 mL with demineral­ 1.00 mg Al: Dissolve 1.000 g Al powder in a ized water. minimum of HC1 (1 + 1). Heat to increase rate 5.8 Mixed-salt standard stock solution I: of dissolution. Add 10.0 mL HC1 (1 + 1) and Dissolve, by appropriate means, the following dilute to 1000 mL with demineralized water. compounds or elements: Cd splatters (0.200 g), 5.2 Cesium chloride solution, 4 g/L: Dissolve Cr metal (0.800 g), Co metal (1.200 g), Cu shot 4 g CsCl of at least 5/9ths purity «10 ppm (0.800 g), Pb shot (2.000 g), Li2CO3 (2.130 g), impurities) in demineralized water and dilute to Mn flakes (2.000 g), Ni powder (1.200 g), SrC03 1L. (1.685 g), and Zn powder (0.320 g). Add 20 mL METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 537 concentrated HC1 (sp gr 1.19), and dilute to 1,000 5.12 Working standard solutions 4, 5, and 6: mL with demineralized water. This solution will Pipet 10 mL (standard 4), 6 mL (standard 5), and contain the following concentrations: Cd (200 2 mL (standard 6) mixed-salt standard stock mg/L), Cr (800 mg/L), Co (1200 mg/L), Cu (800 solution III into 100-mL volumetric flasks. Add mg/L), Pb (2000 mg/L), Li (400 mg/L), Mn (2000 2 mL concentrated HC1 (sp gr 1.19) and 10 mL mg/L), Ni (1200 mg/L), Sr (1000 mg/L), and Zn CsCl solution (5.2) to each flask, and dilute to (320 mg/L). Store in a plastic or Tfeflon bottle 100 mL with demineralized water. Store in 5.9 Mixed-salt standard stock solution II: plastic or Tfeflon bottles and prepare fresh dai­ Dilute 100 mL of mixed salt standard stock solu­ ly. Concentrations are as follows: tion I (5.8) and 20 mL concentrated HC1 (sp gr 1.19) to 1,000 mL with demineralized water. This Standard 4 Standard 5 Standard 6 solution will contain the following concentra­ Constituent (mg/L) (mg/L) (mg/L) tions: Cd (20 mg/L), Cr (80 mg/L), Co (120 mg/L), Al 150 90 30 Cu (80 mg/L), Pb (200 mg/L), Li (40 mg/L), Mn Fe 100 60 20 Mg 20 12 4 (200 mg/L), Ni (120 mg/L), Sr (100 mg/L), and Zn Mn 4 2 1 (32 mg/L). Alternatively, certified standard solu­ tions for each constituent may be purchased and 5.13 Working standard solutions 7, 8, and 9: the mixed standard solution prepared. Store in Pipet 10 mL of standards 4, 5, and 6 (5.12) into a plastic or Tfeflon bottle This solution is stable 100-mL volumetric flasks. Add 2 mL concen­ for 3 months. trated HC1 (sp gr 1.19) and 10 mL CsCl solution 5.10 Mixed-salt standard stock solution III: (5.2) to each flask, and dilute to 100 mL with de- Dissolve, by appropriate means, the following mineralized water. Store in plastic or Ifeflon bot­ compounds or elements: Al powder (1.500 g), tles and prepare fresh daily. Concentrations are CaCO3 (1.249 g), Fe wire (1.000 g), Mg rod (0.200 as follows: g)t Mn flakes (0.040 g), KC1 (0.668 g)t NaCl (0.636 g), and (NH4)2TiO(C204)2'H20 (1.227 g). Add 20 i Standard 7 Standard 8 Standard 9 mL concentrated HC1 (sp gr 1.19), and dilute to Constituent (mg/L) (mg/L) (mg/L) 1,000 mL with demineralized water. This solution Ca 5.0 3 1 will contain the following concentrations: Al K , 3.5 2.1 .7 (1,500 mg/L), Ca (500 mg/L), Fe (1,000 mg/L), Mg Na 2.5 1.5 .5 (200 mg/L), Mn (40 mg/L), K (350 mg/L), Na (250 mg/L), and Ti (200 mg/L). Store in a plastic or 5.14 Nitric acid, concentrated (sp gr 1.41). Tbflon bottle 5.15 Perchloric acid, concentrated, 70- to 5.11 Working standard solutions 1, 2, and 3: 72-percent (sp gr 1.67), Pipet 10 mL (standard 1), 5 mL (standard 2), and 5.16 Sodium standard solution, 1,00 mL = 1 mL (standard 3) mixed-salt standard stock solu­ 1.00 mg Na: Dissolve 2.542 g NaCl in demineral­ tion II into 200-mL volumetric flasks. Add 4 mL ized water, add 20 mL HC1 (sp gr 1.19), and dilute concentrated HC1 (sp gr 1.19) and 20 mL mixed- to 1,000 mL with demineralized water. salt standard stock solution III (5.10) to each 5.17 Titanium standard solution, 1.00 mL = flask, and dilute to 200 mL with demineralized 1.00 mg TL: Dissolve 6.135 g (NH4)2TiO(C2O4)2- water. Store in plastic or Tfeflon bottles and H2O in demineralized water, and dilute to 1,000 prepare fresh daily. Concentrations are as follows: mL with demineralized water. 5.18 Titanium working standard solutions: Standard 1 Standard 2 Standard 3 Pipet 2 mL, 1 mL, and 0.5 mL of titanium stand­ Constituent (mg/D (mg/L) (mg/L) ard solution (5.17) into 100-mL volumetric flasks. Cd 1 0.5 0.10 Cr 4 2 .40 Add 10 mL aluminum standard solution (5.1), 5 Co 6 3 .60 mL iron standard solution (5.7), 3.5 mL sodium Cu 4 2 .40 standard solution (5.16), 10 mL CsCl solution Pb 10 5 1.00 (5.2), and 2 mL concentrated HC1 (sp gr 1.19) to Li 2 1 .20 Ni 6 3 .60 each flask, and dilute to 100 mL with deminer­ Sr 5 2.5 .5 alized water. The standards contain 20, 10, and Zn 1.6 0.8 .16 5 mg/L titanium, respectively. 538 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 6. Procedure 6.11 Remove the beakers from the hotplate, Immediately before each use, clean all and lower the temperature of the hotplate to glassware by rinsing, first with dilute HC1 100°C. Add 2 mL dilute HC1 (1 + 1) to each (1 + 1), and then with demineralized water. beaker and swirl; add 10 mL demineralized 6.1 Dry the sediment sample by an ap­ water to each beaker, mix, and return to the propriate procedure such as freeze-drying or hotplate to dissolve the residue. oven drying at 105 °C. 6.12 Cool the solutions, and pour each into a 6.2 If the sediment sample is greater than 50-mL volumetric flask. Rinse the beaker 100 g, split to less than 100 g by the use of a several times with demineralized water and non-metallic sample splitter (riffle sampler) or bring to volume with demineralized water by coning and quartering. (NOTE 3). Pour the solutions into acid-rinsed 6.3 Grind the sample with a mixer ir"'U or plastic bottles for storage. These solutions with an agate mortar and pestle until all represent a dilution factor of 100 X . material is finer than 100 mesh. NOTE 3. If a sample contained a large amount 6.4 Weigh and transfer 0.5000 g of finely of organic matter, the final solution will com­ ground sample to a 100 mL Teflon beaker; monly contain black "flecks." These can be ig­ weigh appropriate reference standard materials nored if they are allowed to settle before as well (NOTE 1). aspiration of the solutions into an atomic ab­ NOTE 1. The procedure can be used with sam­ sorption spectrometer. ple weights between 0.2500 and 1.000 g, with 6.13 Pipet 5 mL from the 100 X solutions appropriate adjustments to the final-solution (paragraph 6.12) into 50-mL volumetric flasks. volumes and acid strengths (paragraphs 6.4 Add 1 mL concentrated HC1 (sp gr 1.19) and 5 through 6.12). Weights greater than 1.000 g mL CsCl solution (paragraph 5.2) (NOTE 4) to may be used, but may require an extra diges­ each flask, and bring to volume with deminer­ tion with HF and HC1O4 (see steps 6.8 and 6.9). alized water. Pour the solutions into acid-rinsed 6.5 Carry several blanks through the pro­ plastic bottles for storage. These solutions cedure. represent a dilution factor of 1000 X . 6.6 Place hotplate in a perchloric acid hood, NOTE 4. The cesium chloride acts as an ioniza- and adjust the hotplate to produce a surface tion suppressant. temperature of 200 °C. 6.14 Pipet 5 mL from the 1000 X solutions 6.7 Add 6 mL concentrated HNO3 (sp gr (paragraph 6.13) into 50-mL volumetric flasks. 1.41) to each beaker and place the beakers on Add 1 mL concentrated HC1 (sp gr 1.19) and 5 the hotplate for approx 30 min (NOTE 2). mL CsCl solution (paragraph 5.2) to each, and NOTE 2. CAUTION: This step is designed to oxi­ bring to volume with demineralized water. Pour dize organic matter in the sample This step must the solutions into acid-rinsed plastic bottles for be carried out prior to the addition of perchloric storage* These solutions represent a dilution acid; otherwise, a violent explosion could occur. factor of 10,000 X . 6.8 Remove the beakers from the hotplate 6.15 Set up the atomic absorption spectro­ and wait 5 min. Add 6 mL HF (sp gr 1.17 and meter as outlined in paragraph 4.2, and analyze 2 mL HC1O4 (sp gr 1.67), and return the beakers the 100 X solutions (paragraph 6.12) for Cd, Cr, to the hotplate. Continue heating the beakers Co, Cu, Pb, Ni, and Zn using standards 1, 2, until white perchloric fumes are produced and and 3 (paragraph 5.11). Dilute samples if the solution has reached incipient dryness; required. however, do not bake the residues. 6.16 Pipet 5.0 mL of each sample (paragraph 6.9 Remove the beakers from the hotplate 6.12) and working standard solution (paragraph and wait 5 min. Repeat paragraph 6.8. 5.11) to an appropriate container. Add 5.0 mL 6.10 Remove the beakers from the hotplate dilute HC1 (1+49) (paragraph 5.5) and 1.0 mL and wait 5 min. Add 2 mL HC1O4 (sp gr 1.67) CsCl solution (paragraph 5.2). Analyze the solu­ and return the beakers to the hotplate. Continue tions for Li and Sr using the atomic-absorption heating until the solution has reached incipient spectrometer conditions outlined in paragraph dryness; however, do not bake the residues. 4.1 (NOTE 5). METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 539 NOTE 5. The added dilution is required to printer output while aspirating each sample, eliminate interferences due to density differ­ and record the results. The concentration of ences (Abbey, 1967). each constituent (in mg/kg) is obtained by 6.17 Set up the atomic-absorption spectrom­ multiplying the concentration in each sample eter as outlined in paragraph 4.2, and analyze solution by 200, if no dilutions are made. the 1000 X solutions (paragraph 6.13) for Fe, 7.3 Determine the concentration of each con­ Mn, Mg, and Al using standards 4, 5, and 6 stituent (Fe, Mn, Al, Mg, and Ti) from the (paragraph 5.12). Dilute samples if required. digital display or printer output while aspirat­ 6.18 Set up the atomic-absorption spectrom­ ing each sample, and record the results. The con­ eter as outlined in paragraph 4.2, and analyze centration of each constituent (in mg/kg) is 1000 X solutions (paragraph 6.13) for Ti, using obtained by multiplying the concentration in the titanium working standards (paragraph each sample'solution by 1000, if no dilutions are 5.18) (NOTE 6). made. j NOTE 6. Titanium determinations by atomic 7.4 Determine the concentration of each con­ absorption are subject to severe interferences stituent (Ca, K, and Na) from the digital display and sensitivity is heavily dependent on flame or printer output while aspirating each sample, stoichiometry (Walsh, 1977). Adjust the nitrous and record the results. The concentration of oxide flame until it is nearly luminous (increase each constituent (in mg/kg) is obtained by multi­ the fuel flow until the reducing red cone turns plying the concentration in each sample solution orange-yellow, then reduce the fuel flow until by 10,000, if no dilutions are made. the flame just becomes red again). 6.19 Set up the atomic absorption spectrom­ eter as outlined in paragraph 4.2, and analyze 8. Report the 10,000 X solutions (paragraph 6.14) for Ca, Report aluminum, calcium, iron, majjnesium, potassium, sodium, and titanium, total, concen­ K, and Na using standards 7, 8, and 9 (para­ graph 5.13). Dilute samples if required. trations to the nearest 1000 mg/kg (0.1 percent). Report manganese, total, concentration to the 7. Calculations nearest 100 mg/kg (0.01 percent). Report cad­ 7.1 Determine the concentration of each con­ mium, total, concentrations to the nearest 0.1 stituent (Cd, Cr, Co, Cu, Pb, Ni, and Zn) from the mg/kg. Report chromium, cobalt, copper, lead, digital display or printer output while aspirating lithium, nickel, strontium, zinc, total, concen­ each sample, and record the results. The concen­ trations to the nearest 1 mg/kg. tration of each constituent (in mg/kg) is obtained by multiplying the concentration in each sample 9. Precision solution by 100, if no dilutions are made 9.1 The precision for five replicates ex­ 7.2 Determine the concentration of each con­ pressed in terms of relative standard deviation stituent (Li and Sr) from the digital display or is as follows:

Relative Relative Sample standard Sample standard mean deviation mean deviation Constituent (percent) (percent) (percent) (percent) Aluminum 2.4 2 I 8.7 3 Calcium .7 7 7.7 3 Iron 1.8 0 ;10.8 2 Magnesium .44 2 3.8 4 Manganese .02 25 .14 0 Potassium .6 8 3.7 2 Sodium .6 15 I 2.9 3 Titanium .2 5 1.4 4 540 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS 9.2 The precision for six replicates expressed in terms of relative standard deviation is as follows:

Relative Relative Sample standard Sample standard mean deviation mean deviation Constituent (mg/kg) (percent) (mo/kg) (percent) Cadmium 0.4 20 10.0 4 Chromium 8 13 102 3 Cobalt 6 17 44 5 Copper 10 20 106 2 Lead 13 7 708 1 Lithium 8 13 132 4 Nickel 3 33 51 2 Strontium 163 4 475 3 Zinc 80 4 134 2

References Pinta,M., 1982, Modern methods for trace element analysis, Abbey, SM 1967, Analysis of rocks and minerals by atomic translated by STS Inc., Ann Arbor, Ann Arbor Science, absorption spectroscopy, part 1, determination of mag­ Publishers, 492 p. nesium, lithium, zinc, and iron, Geological Survey of Canada Paper 67-37, 35 p. Walsh, J., 1977, Interferences in the determination of Johnson, W. M., and Maxwell, J. A., 1981, Rock and mineral titanium in silicate rocks and minerals by flame analysis, 2d ed. : New York, John Wiley and Sons, atomic absorption spectrophotometry, Analyst, v. 102, 489 p. p. 972. Metals, minor, total-in-sediment, atomic absorption spectrometric, hydride

Parameters and Codes: Metals, total (1-5475-85): none assigned Arsenic (mg/kg as As) ; Antimony (mg/kg as Sb) Selenium (mg/kg as Se) ;

1. Application to the +4 valence state for subsequent quan- 1.1 This method may be used to analyze titation. Separate aliquots are then heated with suspended and bottom sediment for the deter­ a reductant; a stabilizer is added, and arsenic mination of total concentrations of arsenic, an­ and antimony are determined. All determina­ timony, and selenium. The upper and lower tions are made by hydride generation, coupled concentration reporting limits are specified with atomic absorption spectrometry. below. Samples containing analyte concentra­ 2.2 Additional information on the principles tions greater than the upper limit may be of the method can be found in Thompson and analyzed after appropriate dilution. Thomerson (1974), Aslin (1976), Chapman and Dale (1979)j Johnson and Maxwell (1981), Crock and Lichte (1982), and Narasaki and Ikeda (1984). i Lower limit Upper limit Constituent (mg/kg) (mg/kg) i Arsenic 0.05 5.0 3. Interferences Antimony 0.05 5.0 3.1 Total digestion, dilution, and hydride Selenium 0.05 5.0 generation frees the arsenic, antimony and selenium from the original matrix, and minimizes interferences. Mixed-salt standards 1.2 Analyses must be performed on dried for antimony and selenium, and background and ground samples that have been solubilized correction for selenium, further compensate for with a combination of nitric, hydrofluoric, and any interferences. perchloric acids heated in open Teflon beakers. 3.2 Interferences, primarily negative, do oc­ These solutions are then analyzed by atomic ab­ cur and are documented by Johnson land Max­ sorption spectrometry, coupled with hydride well (1981), and Narasaki and Ikeda (1984). generation. 4. Apparatus 2. Summary of method 4.1 Atomic absorption spectrometer 2.1 A sediment sample is dried, ground, and equipped with electronic digital readout, auto­ homogenized, and then is digested with a com­ matic zero and concentration controls, and a bination of nitric, hydrofluoric, and perchloric deuterium-source background corrector; an acids in a Teflon beaker heated on a hotplate autosampler and printer or chart recorder per­ at 200 °C. The resulting salts are dissolved in mits automation of the analytical process. concentrated hydrochloric acid and demineral- 4.2 Refer to the manufacturer's manual to ized water. This serves to reduce the selenium optimize the instrument for the following: 541 542 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS

Grating: ultra- Wavelength Background Constituent vlolet(uv) (nm) Burner Fuel Oxldant Flame type correction

As UV 193.7 N20 C2H2 air lean Off Sb UV 217.6 air lean Off Se UV 196.0 N20 C2H2 air lean on

The N2O burner head is used because of its centrated HC1 (sp gr 1.19), and dilute to volume shorter flame width. This burner produces very with demineralized water. Store in plastic bot­ good analytical results while considerably tle. Solution should be remade weekly. extending the life of the quartz cell. The effect 5.8 Mixed-salt standard solution I: Dissolve, of the N2O burner may vary with different by appropriate means, the following compounds instrumentation. or elements: Cd splatters (0.200 g), Cr metal 4.3 Hydride generator, Varian VGA 76 or (0.800 g), Co metal (1.200 g), Cu shot (0.800 g), equivalent. This system consists of a peristaltic Pb shot (2.000 g), Li2CO3 (2.130 g), Mn flakes pump, reaction coil, gas-liquid separator, and a (2.000 g), Ni powder (1.200 g), SrCO3 (1.685 g), flame-heated quartz cell. and Zn powder (0.320 g). Add 20 mL concen­ 4.4 Beakers, Teflon, 100-mL capacity, thick- trated HC1 (sp gr 1.19), and dilute to 1000 mL walled, capable of withstanding temperatures with demineralized water. This solution will con­ as high as 260 °C. tain the following concentrations: Cd (200 4.5 Hotplate, gas or electric, capable of mg/L), Cr (800 mg/L), Co (1200 mg/L), Cu (800 reaching at least 250 °C. mg/L), Pb (2000 mg/L), Li (400 mg/L), Mn (2000 4.6 Perchloric acid hood, with appropriate mg/L), Ni (1200 mg/L), Sr (1000 mg/L), and Zn washdown facility and gas or electrical outlets. (320 mg/L). Store in plastic or Teflon bottle. 5.9 Mixed-salt standard solution II: 5. Reagents Dissolve, by appropriate means, the following 5.1 Antimony standard solution, 1.00 mL = compounds or elements: Al powder (1.500 g), 1000 f*g Sb: Dissolve 1.0000 g Sb metal in 10 CaCO3 (1.249 g), Fe wire (1.000 g), Mg rod mL concentrated HNO3 (sp gr 1.41) plus 5 mL (0.200 g), Mn flakes (0.040 g), KC1 (0.688 g), concentrated HC1 (sp gr 1.19). Dilute to 1000 NaCl (0.636 g), and (NH^TKXCgO^'HsjO mL with dilute HC1 (1 + 1). (1.227 g). Add 20 mL concentrated HC1 (sp gr 5.2 Arsenic standard solution, 1.00 mL = 1.19), and dilute to 1000 mL with demineralized 1000 fig As: Dissolve 1.3203 g As2O3 in a mini­ water. This solution will contain the following mum of concentrated HC1 (sp gr 1.19). Dilute concentrations: Al (1500 mg/L), Ca (500 mg/L), to 1000 mL with dilute HC1 (1 + 1). Fe (1000 mg/L), Mg (200 mg/L), Mn (40 mg/L), 5.3 Hydrochloric acid, concentrated (sp gr K (350 mg/L), Na (250 mg/L), and Ti (200 mg/L). 1.19). Store in plastic or Teflon bottle. 5.4 Hydrochloric acid, dilute (1 + 1): Add 5.10 Nitric acid, concentrated (sp gr 1.41). 500 mL concentrated HC1 (sp gr 1.19) to 500 mL 5.11 Oxalic acid solution, saturated: Dissolve demineralized water. Store in glass or plastic approximately 150 g oxalic acid in demineral­ bottle. ized water using mild heating. Cool until 5.5 Hydroxylamine hydrochloride solution, crystallization stops. in a saturated solution of oxalic acid: Dissolve 5.12 Perchloric acid, concentrated, 70- to 200 g NH2OH-HC1 in 800 g of saturated solu­ 72-percent (sp gr 1.67). tion of oxalic acid. 5.13 Potassium iodide solution, 100 g/L: 5.6 Hydrofluoric acid, concentrated, 48- to Dissolve 100 g KI in demineralized water and 51-percent (sp gr 1.17). dilute to 1 L. Store in plastic bottle. 5.7 Mixed-element standard solution, 1.00 5.14 Selenium standard solution, 1.00 mL = 50.0 jig Sb, As, and Se: Pipet 10.0 mL of mL = 1000 jig Se: Dissolve 1.0000 g Se metal each element standard solution (As, Sb, Se) in­ in 5 mL concentrated HNO3 (sp gr 1.41). Dilute to a 200-mL volumetric flask. Add 100 mL con­ to 1000 mL with dilute HC1 (1 + 1). METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 543 5.15 Sodium borohydrate solution, 0.6 g/100 weigh appropriate reference standard materials mL: Dissolve 3.0 g NaBH4 and 2.5 g NaOH in (NOTE 1). j demineralized water and dilute to 500 mL. NOTE 1. The procedure can be used with sam­ 5.16 Working standard solutions 1,2,3: Pipet ple weights between 0.2500 and 1.000 g, with 200 pL (standard 1), 100 jiL (standard 2), and appropriate! adjustment to the final solution 8 /iL (standard 3) of the mixed-element stand­ volumes and acid strengths (paragraphs 6.4 ard solution into 200-mL volumetric flasks. Add through 6.12). Weights greater than 1.000 g 100 mL concentrated HC1 (sp gr 1.19), 1 mL may be used; but will require an extra digestion mixed-salt standard stock solution I, and 20 mL with HF and HC1O4 (see paragraphs 6.8 and mixed-salt standard stock solution II to each 6.9). flask and dilute to 200 mL with demineralized 6.5 Carry several blanks (reagents only) water. Store in plastic or Teflon bottles and through the procedure. prepare fresh daily. Concentrations are as 6.6 Place hotplate in a perchloric acid hood follows: and adjust to produce a surface temperature of 200 °C. 6.7 Add 6 mL concentrated HNO3 (sp gr Standard 1 Standard 2 Standard 3 Constituent (nfl/U 1.41)—CAUTION: Explosive with peirchloric Sb 50 25 2 acid—to each beaker and place the betikers on Se 50 25 2 the hotplate. Continue heating until the residue is nearly dry, approx 30 min. If sample is still evolving brown fumes of NOX at this point, 5.17 Working standard solutions 4, 5, 6: repeat this step (NOTE 2). Pipet 200 /iL (standard 4), 100 jiL (standard 5), NOTE 2. CAUTION: This step is desiigned to and 8 /iL (standard 6) mixed-element standard oxidize organic matter in the sample. This step solution into 200-mL volumetric flasks. Add 100 must be carried out prior to the addition of per­ mL concentrated HC1 (sp gr 1.19) to each flask, chloric acid; otherwise, a violent explosion could and dilute to 200 mL with demineralized water. occur. Store in plastic or Teflon bottles. Concentra­ 6.8 Remove the beakers from the hotplate tions are as follows: and cool for; 5 min. Add 6 mL HF (sp gr 1.17) and 2 mL HC1O4 (sp gr 1.67), and return the beakers to the hotplate. Continue heating the Standard 4 Standard 5 Standard 6 Constituent beakers until dense, white perchloric fumes have been produced and the solution has reached As 50 25 incipient dryness; however, do not bake the residues. 6.9 Remove beakers from the hotplate and 6. Procedure cool for 5 mm; repeat paragraph 6.8. Immediately before each use, clean all glass­ 6.10 Remove beakers from the hotplate and ware by rinsing first with dilute HC1 (1 + 1) and cool for 5 min. Add 2 mL HC1O4 (sp gr 1.67) then with demineralized water. and return the beakers to the hotplate. Continue 6.1 Dry the sediment by freeze-drying or air- heating until the solution has reached incipient drying at room temperature. dryness; however, do not bake the residues. 6.2 If the sediment sample is greater than 6.11 Remove the beakers from the hotplate, 100 g, split to less than 100 g by the use of a and lower the temperature of the hotplate to nonmetalic sample splitter (riffle sampler) or by 100 °C. Add 25 mL concentrated HC1 (sp gr coning and quartering. 1.19) to each beaker and swirl; return to hotplate 6.3 Grind the sample with a mixer mill or an to dissolve the residue. agate mortar and pestle until all material is finer 6.12 Cool the solutions, and pour each into a than 100 mesh. 50-mL volumetric flask. Rinse the beaker 6.4 Weigh and transfer 0.5000 g of finely several times with demineralized water and ground sample to a 100-mL Teflon beaker; dilute to the mark with demineralized water 544 TECHNIQUES OF WATER-RESOURCES INVESTIGATIONS (NOTE 3). Pour the solutions into acid-rinsed As and Sb standards and blanks alternately plastic bottles for storage. until stable readings are attained for each. NOTE 3. If a sample contained a large amount Analyze the solutions for As and Sb using work­ of organic matter, the final solution will com­ ing standards 1, 2, and 3 for Sb, and working monly contain black "flecks." Allow the flecks standards 4,5, and 6 for As. Dilute the samples to settle before pumping the solutions into the if required. (NOTE 5) hydride generator. NOTE 5. With use, the quartz cell may become 6.13 Determination of selenium: coated with a white layer of oxides. If left on 6.13.1 Feed the concentrated HC1 (sp gr 1.19) the cell, these oxides can cause the cell to crack and NaBH4 solution into the hydride generator when heated. To remove the oxides, soak the using demineralized water in the sample line. cell for a short time (10 to 15 min is usually suf­ 6.13.2 Set up the atomic absorption spec­ ficient) in concentrated HF (sp gr 1.17); then trometer as outlined in paragraph 4.2. Allow the rinse the cell thoroughly to remove any traces quartz cell to come to thermal equilibrium (ap- of HF. A strong (45-percent) solution of NaOH prox 5 min). Analyze the 50 figfL of Se and blank or KOH may be used in place of HF. alternately until stable readings are attained for each. Analyze the solutions (paragraph 6.12) for 7. Calculations selenium, using working standards 1, 2, and 3. 7.1 Determine the concentration of As, Sb, Dilute the samples if required. and Se (in /ig/L) from the digital display, printer, 6.14 Determination of antimony and or chart recorder, and record the results. arsenic: 7.2 To convert the results from pg/L to 6.14.1 Pipet 20 mL of each sample (para­ mg/kg, use the following equation: graph 6.12), working standard solutions 1, 2f and 3 (Sb), and working standard solutions 4, As, Sb, or Se (mg/kg) = 5, and 6 (As) into 18 X 150-mm (or larger) test mL digest tubes. Add 2 mL KI solution and heat in a dry (As, Sb, or Se) X bath at 90 °C for 1 h. Allow to cool, add 2 mL 1000 NH2QH*HCl/oxalic acid solution, and mix wt of sample (g) thoroughly with a vortex mixer (NOTE 4). NOTE 4. The addition of KI reduces the As and Sb to valence states most favorable to hydride 8. Report generation (+3). The addition of the NH2OH- Report the concentration of each determined HCl-oxalic acid solution was found to stabilize constituent to the nearest 0.1 mg/kg. the solutions and to give more consistent results. The oxalic acid also appears to minimize 9. Precision interference from Fe (Crock and Lichte, 1982). The precision for ten replicates on U.S. 6.14.2 Set up the atomic absorption spec­ Geological Survey and National Bureau of trometer as outlined paragraph section 4.2. Standards reference materials expressed in Allow the quartz cell to come to thermal terms of relative standard deviation is as equilibrium (approx 5 min). Analyze the 50 /*g/L follows:

Mean sample 1 Relative standard Mean sample 2 Relative standard mean deviation mean deviation Constituent (mg/kg) (percent) (mg/kg) (percent)

Arsenic 0.4 25 12.4 9 Antimony .4 13 3.3 6 Selenium .5 13 3.4 4 METHODS FOR DETERMINATION OF INORGANIC SUBSTANCES 545 References generation-atomic absorption spectrometry: Analytica Chimica Acta, v. 144, p. 223-233. Aslin, G. E. M.v 1976, The determination of arsenic and an­ Johnson, W. M., and Maxwell, J. A., 1981, Rock and mineral timony in geological materials by flameless atomic ab­ analysis, 2d ed. : New York, John Wiley and Sons, sorption spectrometry: Journal of Geochemical 489 p. j Exploration, v. 6, p. 321-330. Narasaki, Hisatake, and Ikeda, Masahiko, 1984, Automated Chapman, J. F., and Dale, L. S., 1979, Atomic absorption determination of arsenic and selenium by atomic absorp­ spectrometric determination of some elements forming tion spectrometry with hydride generation: Analytical volatile hydrides with a heated cell atomizer and gas Chemistry, v. 56, p. 2059-2063. handling system: Analytica Chimica Acta, v. Ill, Thompson, K. C., and Thomerson, D. R., 1974, Atomic ab­ p, 137-144. sorption studies on the determination oi antimony, Crock, J. GM and Lichte, F. E., 1982, An improved method bismuth, germanium, lead, selenium, tellurium and tin for the determination of trace levels of arsenic and an­ by utilizing the generation of covalent hydrides: timony in geologic materials by automated hydride Analyst, y. 99, p. 595-601.

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