WI 050114.01

T 438

DRAFT NO. 5

DATE July 27, 2006 TAPPI WORKING GROUP CHAIRMAN J Ishley

SUBJECT CATEGORY Fillers & Pigments Testing

RELATED METHODS See “Additional Information”

CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals.

Zinc and cadmium in paper (Reaffirmation of T 438 cm-96)

(no changes were made since last draft)

1. Scope and significance

1.1 This method maybe used for the determination of cadmium and zinc either in paper or in highly opaque pigments. Zinc is usually present in zinc oxide, zinc sulfide, or as lithopone (a combination of zinc sulfide and barium sulfate), which is occasionally used in filled paper, in paper coatings and in high-pressure laminates and wallpaper. Some forms of zinc oxide have photoelectric properties and are found in certain papers used for photo reproduction. Zinc or cadmium pigments are sometimes added to papers to cause fluorescence, and zinc oxide has been used to enhance the cohesive strength of some types of paper coatings. 1.2 Three procedures for each element are described: polarographic, either gravimetric or volumetric, and atomic absorption. The gravimetric procedure is suitable if a polarograph is not available. For the determination of zinc in a zinc-bearing pigment, the volumetric procedure is recommended, because the polarographic procedure is insensitive

Approved by the Standard Specific Interest Group for this Test Method TAPPI T 438 cm-96 Zinc and cadmium in paper / 2

over 25% Zn levels. The polarographic procedure can be used for the determination of zinc and cadmium in paper and for cadmium in cadmium bearing pigments. The preferred procedure for each material is based on its concentration. 1.3 When zinc is to be determined volumetrically (cadmium absent) one precipitation of heavy metals with washing is sufficient. 1.4 In the atomic absorption procedure, sensitivities for 1% absorption are 0.02 mg/mL Zn and 0.03 mg/mL Cd, respectively. The repeatability of this procedure is questionable at present for Zn and Cd concentrations of greater than 5%.

2. Polarographic procedure

2.1 Apparatus. 2.1.1 Polarograph, of the manually operated type. A recording polarograph may be used, although this method is written specifically for a manually operated instrument. 2.1.2 Electrolysis equipment, including a cell, a dropping mercury electrode, an arrangement for maintaining a constant head of mercury above the capillary, and a constant-temperature bath. The cell may be of simple design; for example a test tube is 15 x 85 mm. This cell is fitted with a three-hole notched rubber stopper that will hold the dropping mercury electrode, the contact electrode for the anode (a pool of mercury), and a tube for flushing the solution with nitrogen. 2.1.3 Nitrogen cylinder and tubing. 2.1.4 Other apparatus: pipets, 5, 15, 20, and 50 mL; three 200 mL volumetric flasks. 2.2 Reagents. 2.2.1 Standard zinc solution (1 mL = 0.0010 g of Zn): Dissolve 1.245 g of freshly ignited ZnO in 50 mL of hot HCl (1:10). Cool, dilute with water to 1000 mL in a volumetric flask, and mix.

2.2.2 Standard cadmium solution (1 mL = 0.0010 g of Cd): Dissolve 1.631 g of anhydrous CdCl2 in 100 mL of hot water. Cool, dilute to 100 mL in a volumetric flask and mix. 2.2.3 Gelatin solution (2 g/1000 mL): Dissolve 2.00 g of gelatin in boiling water and dilute the clear solution to 1000 mL. 2.2.4 Nitrogen (with minimum oxygen content).

2.2.5 NH4Cl (crystalline). 2.2.6 HCl (12 N).

2.2.7 NH4OH (14.8 N).

2.2.8 HNO3 (15.7 N). 2.3 Sampling and test specimen. 2.3.1 From each test unit obtained in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product” (for paper) or TAPPI T 657 “Sampling of Fillers and Pigments” (for pigments), prepare a specimen sufficient to contain at least 10 mg of zinc or 10 mg of cadmium if present. 3 / Zinc and cadmium in paper T 438 cm-96

2.3.2 Normally about 1 g or less of dry paper is sufficient for a single determination; more is needed if its moisture content is unknown. 2.3.3 If the moisture content is unknown, determine it in accordance with TAPPI T 412 “Moisture in Paper and Paperboard.” 2.4 Procedure. 2.4.1 Detailed information regarding the polarographic procedure may be found in the literature (1-3). 2.4.2 Zinc and cadmium factors. 2.4.2.1 Transfer 20.0 and 50 mL aliquots of the standard zinc and cadmium solutions, respectively, to each of two 200 mL volumetric flasks. To each of these flasks, and to a third flask to be carried through the entire procedure as a blank, add 16.6 g of NH4Cl and 5 mL of HCl, and dilute to approximately 150 mL with water. Add 15 mL of NH4OH and 10 mL of gelatin solution. Cool, dilute to the mark with water, and mix. 2.4.2.2 Transfer suitable portions of the resulting solutions to electrolysis cells and remove oxygen by bubbling nitrogen through the solutions for 10 min.

NOTE 1: Since the diffusion current increases with increasing temperature, arrangement must be made to control standards and specimens at a uniform temperature during electrolysis or to make corrections for temperature fluctuations. Other conditions such as drop time and height of the mercury column must also be constant.

2.4.2.3 Determine the increase in the galvanometer deflection in divisions when changing from an applied potential of -0.58 to -0.83 V, and again when changing from -1.09 to -1.40 V for each solution. Adjust the sensitivity of the polarograph circuit so as to obtain optimum increases in galvanometer deflection.

NOTE 2: These voltage settings must be on the residual current plateaus and the diffusion current plateaus, respectively. Since the wave form may be affected by the sensitivity of the galvanometer, a complete polarogram should be plotted and the above settings checked for the particular instrument being used.

2.4.2.4 Multiply the increase in galvanometer deflection obtained by increasing the potential from -0.58 to -0.83 V for each solution by the shunt setting used and plot these values against the amount of cadmium in grams. Next multiply the increase in galvanometer deflection obtained by increasing the potential from -1.09 to -1.40 V for each solution by the shunt settings used and plot these values against the amount of zinc in grams. The three points must fall approximately on a straight line for both metals. T 438 cm-96 Zinc and cadmium in paper / 4

2.4.2.5 Calculate the cadmium and zinc factors as follows:

C1

F1 =

(R1 - B1)

C2

F2 =

(R2 - B2)

where

F1 = cadmium per galvanometer scale division at full sensitivity, gx.

C1 = cadmium in the standard, g.

R1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the standard.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank.

F2 = zinc per galvanometer scale division at full sensitivity, g.

C2 = zinc in the standard, g.

R2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the standard.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank.

NOTE 3: If conditions are kept constant, there is no need to redetermine the cadmium and zinc factors until a new capillary is used.

2.4.3 Analysis of specimen. Transfer about 0.5 g of the dried specimen, weighed to the nearest 0.001 g, to a

400 mL beaker. Add 10 mL of concentrated H2SO4 and heat to char the paper. Oxidize with HNO3 and, when the solution is clear, evaporate to dryness. Add 16.6 g of NH4Cl, 5 mL of HCl, and 50 mL of water. Heat until solution is complete. Cool, transfer to a 200 mL volumetric flask, and dilute to approximately 150 mL with water. Add 15 mL of

NH4OH and 1 mL of gelatin solution. Cool, dilute to 200 mL, and continue in accordance with the procedure for determining the zinc and cadmium factors. 2.4.4 Calculation. Calculate the percentage of cadmium and zinc as follows:

(A1 - B1) F1 Cadmium, % = x 100 W 5 / Zinc and cadmium in paper T 438 cm-96

(A2 - B2) F2 Zinc, % = x 100 W where

A1 = increase galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the specimen.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank, in accordance with the procedure.

F1 = cadmium per galvanometer scale division at full sensitivity, g. W = weight of specimen, g.

A2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the specimen.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank, in accordance with the procedure.

F2 = zinc per galvanometer scale division at full sensitivity, g.

3. Gravimetric and volumetric procedures

3.1 Apparatus. 3.1.1 For cadmium by the gravimetric procedure. 3.1.1.1 Platinum dish, evaporating about 50 mL. 3.1.1.2 Other apparatus: three 400 mL beakers; 25 and 50 mL graduated cylinders; filter funnel with fine filter paper. 3.1.2 For zinc by the volumetric procedure. As for cadmium and in addition: a 3 and a 5 mL pipet (or small graduated cylinder); medium filter paper; 50 mL buret. 3.2 Reagents. 3.2.1 For cadmium by the gravimetric procedure. 3.2.1.1 Sulfuric acid, concentrated; also dilute (1:1). 3.2.1.2 Nitric acid, concentrated.

3.2.1.3 Hydrogen sulfide, H2S (generator or cylinder). 3.2.1.4 Hydrochloric acid, dilute (3:7). 3.2.2 For zinc by the volumetric procedure. 3.2.2.1 As for cadmium, and in addition:

3.2.2.2 Uranyl acetate indicator. Dissolve 5 g of UO2(CH3COO2) - 2H2O in water, acidify with acetic acid, and dilute to 100 mL.

3.2.2.3 Ammonia, dilute NH4OH (1:1). 3.2.2.4 Hydrochloric acid, concentrated; also dilute (1:1). T 438 cm-96 Zinc and cadmium in paper / 6

3.2.2.5 Sulfuric acid, dilute (5:95). 3.2.2.6 Methyl orange indicator. 3.2.2.7 Zinc, metal, reagent grade. 3.2.2.8 Litmus paper.

3.2.2.9 Potassium ferrocyanide, standard solution 1 mL = 0.01 g of Zn): Dissolve 42.3 g of K4Fe(CN6) -3H2O in water and dilute to 1000 mL. To standardize, transfer 0.3200 - 0.3400 g of zinc to a 400 mL beaker, then dissolve in 10 mL of concentrated HCl and 20 mL of water. Add NH4OH until slightly alkaline to litmus paper; then add HCl until just

acid, plus 3 mL in excess. Dilute to about 250 mL with hot water and heat nearly to boiling. Titrate with K4Fe(CN6) solution, while stirring constantly, until a drop tested on a white porcelain plate with a drop of uranyl acetate indicator shows a brown tinge after standing 1 min. Make a blank determination following the same procedure and using the same

amounts of reagents and water. Calculate the zinc factor of the K4Fe(CN6) solution as follows:

F = Cl(A - B) where

F = zinc equivalent of K4Fe(CN6) solution, g/mL.

A = K4Fe(CN6) solution required to titrate the zinc solution, mL.

B = K4Fe(CN6) solution required to titrate the blank, mL. C = zinc used, g.

NOTE 4: Care should be taken in the handling of K4Fe(CN6) because atmosphere oxygen rapidly converts it to K3Fe(CN6).

3.3 Sampling and test specimen. 3.3.1 Sample as previously described for the polarographic procedure (2.3.1) except use a 4 g specimen for the analysis of zinc in zinc pigments. 3.3.2 Normally about 4 g or less of dry paper is sufficient for a single determination of zinc and cadmium in paper. 3.4 Procedures. 3.4.1 For cadmium by the gravimetric procedure. 3.4.1.1 Place about 4 g of the specimen in a tared weighing bottle, dry to constant weight and weigh to the nearest 5 mg. Transfer to a 400 mL beaker and add 20 mL of concentrated H2SO4. Heat to char the paper and add sufficient HNO3 to oxidize the mixture to a clear solution. Evaporate to dryness and add approximately 100 mL of water and 10 mL of 1:1 H2SO4. Heat to dissolve, and filter if there is any insoluble residue. Dilute to approximately 200 mL, and pass a rapid stream of H2S through the solution for 20 min. Filter through fme paper, but do not wash. Reserve the filtrate. 7 / Zinc and cadmium in paper T 438 cm-96

3.4.1.2 Dissolve the precipitate on the paper with cold 3:7 HCl and wash the paper well with water, catching the solution in the same 400 mL beaker. Add 15 mL of 1:1 H2SO4 and evaporate to dense white fumes. Cool, dilute to 200 mL, and reprecipitate as above. 3.4.1.3 Filter, using a fme paper. Combine the filtrate with that reserved above and reserve the combined filtrates for the determination of zinc. Dissolve the precipitate with cold 3:7 HCl followed by washing with water, receiving the solution in a weighed platinum dish. Add 10 mL of 1:1 H2SO4 and evaporate to dense white fumes.

Remove the excess H2SO4 by heating the dish cautiously, and finally heat to 500 - 600°C. Cool, and weigh as CdSO4. 3.4.1.4 Calculation. Calculate the percentage of cadmium as follows:

A x 0.5392 Cadmium, % = x 100 B where

A = weight of CdSO4, g. B = dry weight of specimen, g.

3.4.2 For zinc by the volumetric procedure. 3.4.2.1 Evaporate the combined filtrates, obtained in accordance with the gravimetric procedure for cadmium, to dryness. Add 5 mL of 1:1 H2SO4 and 100 mL of water, and heat to dissolve. Cool, and add 1:4 NH4OH until just

alkaline. Add 1:4 H2SO4 until neutral to methyl orange, and then add 3 mL of 5:95 H2SO4. Dilute to 200 mL and through a short glass tube, pass a rapid stream of H2S through the solution for 40 min. Leave the tube in the beaker and allow the precipitate to settle for 10 min. 3.4.2.2 Filter, using a medium paper, and wash twice with cold water. Discard filtrate. Place the original beaker and gassing tube under the funnel and punch a hole in the paper. Wash the bulk of the ZnS into the beaker, using hot water. Wash the paper with 40 mL of hot 1:4 HCl and again with hot water. Dissolve the zinc sulfide still adhering to the gassing tube with a minimum quantity of hot 1:4 HCl.

3.4.2.3 Boil to expel H2S. Cool, and add NH4OH until slightly alkaline to litmus paper; then add HCl until just acid, plus 3 mL in excess. Dilute to 250 mL with hot water and heat nearly to boiling. Titrate as described previously. 3.4.2.4 Calculation. Calculate the percentage of zinc in the specimen as follows:

(A - B) F Zn, % = x 100 C where

A = K4Fe(CN6) solution required to titrate the specimen, mL.

B = K4Fe(CN6) solution required to titrate the blanks as described under 3.2.2.9. (standardization of potassium ferrocyanide), mL. T 438 cm-96 Zinc and cadmium in paper / 8

F = zinc equivalent of the K4Fe(CN6) solution, g/mL. C = weight of specimen, g.

4. Atomic absorption procedure

4.1 Summary. A paper specimen is reacted with H2SO4 and H2O2. The resulting solution is diluted, and the concentrations of Zn and/or Cd are measured with a atomic absorption spectrophotometer. A calculation of the weight percents of Zn and/or Cd is then made. 4.2 Definition. Linear working range is that concentration range over which instrument response is propor- tional to concentration. 4.3 Apparatus. 4.3.1 Atomic absorption spectrophotometer. 4.3.2 Erlenmeyer flask, 250 mL with 24/40 ground glass opening. 4.3.3 Parallel side arm connector, 3-way, with 24/40 ground glass joint. 4.3.4 Graduated cylindrical funnel, 50 mL with 24/40 ground glass joint. 4.3.5 Hot plate. 4.3.6 Ring stand. 4.3.7 Analytical balance, capable of reading to 0.001 g. 4.3.8 Volumetric glassware, to include at least one of each of the following flasks, 500 mL, 250 mL, and 100 mL; pipets, 50 mL, 25 mL, 10 mL, and 1 mL. 4.4 Reagents and materials. 4.4.1 Stock Zn solution, 500 μg/mL. Prepare by dissolving 0.500 g of zinc metal in a minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl. 4.4.2 Stock Cd solution, 500 μg/mL. Prepare by dissolving 0.500 g of cadmium metal in minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl.

4.4.3 H2SO4, 98% wt./wt.

4.4.4 H2O2, 30% wt./wt. 4.5 Sampling and test specimens. 4.5.1 Obtain a sample in accordance with TAPPI T 400. 4.5.2 Obtain 1 to 2 g of specimen from various positions on each test unit in the form of small strips. 4.5.3 Dry composite test specimen for 1 h at 105°C and place in a desiccator at least 0.5 h before analyzing. 4.6 Procedure. 4.6.1 Weigh to the third decimal place, a specimen between 1 and 2 g. Add test specimen to a 250 mL

Erlenmeyer flask containing 5 mL of concentrated H2SO4. Attach 3-way parallel side arm connector and 50 mL

cylindrical funnel containing approximately 40 mL of 30% H2O2 to the flask. Support glassware with ring stand and place flask on hot plate. Heat the mixture until the specimen is completely charred and dense white fumes appear. Add

H2O2 at a rate of approximately 1 drop per second until a clear solution results. Evaporate the solution to dryness. Then 9 / Zinc and cadmium in paper T 438 cm-96

cool, add 20 mL HCl (1+1) and 50 mL of water and heat until solution is complete. Allow to cool, then transfer contents of the flask into a 1000 mL volumetric flask and dilute to the mark with water. 4.6.2 Prepare calibration standards by diluting stock zinc and cadmium solutions to 0.1, 0.5, and 1.0 g/mL with 1% (v/v) HCl. Set instrumental conditions according to manufacturer's specifications. Instrument operating conditions are given in 4.6.3. Use either absorbence or concentration readout mode depending on how instrument is equipped. Zero instrument with deionized H2O. Measure calibration standards or set concentration readout. Measure specimens in this sequence: specimen, standard, specimen. Make 3 readings on each specimen. If a specimen concentration readout or absorbence falls outside of the linear range suggested by manufacturer or established by experimentation, dilute solution to get response in linear working range. 4.6.3 Instrument operating conditions.

Analytical Light Flame Element (Slit) wavelength source type

Zinc 0.7 nm 213.9 nm Hollow Air- cathode acetylene lamp (lean) Cadmium 0.7 nm 228.8 nm Hollow Air- cathode acetylene lamp (lean)

4.6.4 Calculation. Calculate the percentages of Zn and/or Cd as follows:

AB Cd, % or Zn, % = (105) C where A = concentration of Zn and Cd, μg/mL. B = dilution factor; example: a 10 mL aliquot of solution is diluted to 100 mL; then dilution factor equals 10. C = weight of test specimen, μg.

T 438 cm-96 Zinc and cadmium in paper / 10

5. Report

5.1 Report the amount of zinc or cadmium as a percentage of the moisture-free material, to the nearest 0.1%, and state the procedure used. 5.2 For the atomic absorption procedure, results are to consist of a listing of the following: 5.2.1 Measured absorbances or concentrations. 5.2.2 A graph on which concentrations of Zn and Cd standards are plotted against their absorbences. 5.2.3 A statement of instrumental conditions to include lamp current, wavelength of measurement, type of flame, type of burner, and any special equipment used for the improvement of instrument performance. 5.2.4 A calculation of % Zn and/or Cd. 5.2.5 Notes on any observances of unusual behavior of either the instrument or the reaction.

6. Precision

6.1 Repeatability: all repeatability values are based on the amount present.

Material Method Repeatability

Zn (0-25%) Polarographic 1% Cd (0-25%) Polarographic 1% Zn (>25%) Volumetric 1% Cd Gravimetric 0.5% Zn (0-5%) Atomic absorption 2% Cd (0-5%) Atomic absorption 2%

6.2 Reproducibility: not known; 6.3 Comparability: not known, in accordance with definition of above terms used as defined in TAPPI T 1200 “Interlaboratory Evaluation of Test Methods to Determine TAPPI Repeatability and Reproducibility.”

7. Additional Information

7.1 Effective date of issue: to be assigned. 7.2 In the atomic absorption method, the extent of interferences from other ions has not been fully examined; however, the absorbances of Zn and Cd are not significantly affected by 10-fold excesses of each other. Ca in a 10-fold 11 / Zinc and cadmium in paper T 438 cm-96

excess depresses Zn absorbance slightly. Ti in a 10-fold excess seems to have no effect on Zn absorbance. Sulfuric acid enhances both absorbances. 7.2.1 Detection limits can be significantly improved by the use of a graphite tube furnace in the atomic absorption procedure. 7.2.2 The atomic absorption procedure can be applied to many other metal ions (5). 7.3 Related method: ASTM D-1224.

References

1. Kolthoff, I. M., and Ligane, J. J., Polarography, 2nd edn., Vol. 2, Interscience, New York, 1952. 2. Muller, O. H., “The Polarographic Method of Analysis,” J. Chem. Educ., Feb.-July, 1981. 3. Strong, C. L., “How to Build a Polarograph,” Scientific American 226 (9): 247 (1962). 4. Atomic Absorption Product Department, Perkin-Elmer Corp., Analytical Methods for Atomic Absorption Spectrophotometry, 1973. 5. Price, J. P., “Utilization of Atomic Absorption Spectroscopy in the Synthetic Fiber Industry,” Tappi 54 (9):1497 (1971).

Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Director of Quality and Standards. g

WI 050114.01

T 438

DRAFT NO. 4

DATE March 2, 2006 TAPPI WORKING GROUP CHAIRMAN J Ishley

SUBJECT CATEGORY Fillers & Pigments Testing

RELATED METHODS See “Additional Information”

CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals.

Zinc and cadmium in paper (Reaffirmation of T 438 cm-96)

(no changes were made since last draft)

1. Scope and significance

1.1 This method maybe used for the determination of cadmium and zinc either in paper or in highly opaque pigments. Zinc is usually present in zinc oxide, zinc sulfide, or as lithopone (a combination of zinc sulfide and barium sulfate), which is occasionally used in filled paper, in paper coatings and in high-pressure laminates and wallpaper. Some forms of zinc oxide have photoelectric properties and are found in certain papers used for photo reproduction. Zinc or cadmium pigments are sometimes added to papers to cause fluorescence, and zinc oxide has been used to enhance the cohesive strength of some types of paper coatings. 1.2 Three procedures for each element are described: polarographic, either gravimetric or volumetric, and atomic absorption. The gravimetric procedure is suitable if a polarograph is not available. For the determination of zinc in a zinc-bearing pigment, the volumetric procedure is recommended, because the polarographic procedure is insensitive

Approved by the Standard Specific Interest Group for this Test Method TAPPI T 438 cm-96 Zinc and cadmium in paper / 2

over 25% Zn levels. The polarographic procedure can be used for the determination of zinc and cadmium in paper and for cadmium in cadmium bearing pigments. The preferred procedure for each material is based on its concentration. 1.3 When zinc is to be determined volumetrically (cadmium absent) one precipitation of heavy metals with washing is sufficient. 1.4 In the atomic absorption procedure, sensitivities for 1% absorption are 0.02 mg/mL Zn and 0.03 mg/mL Cd, respectively. The repeatability of this procedure is questionable at present for Zn and Cd concentrations of greater than 5%.

2. Polarographic procedure

2.1 Apparatus. 2.1.1 Polarograph, of the manually operated type. A recording polarograph may be used, although this method is written specifically for a manually operated instrument. 2.1.2 Electrolysis equipment, including a cell, a dropping mercury electrode, an arrangement for maintaining a constant head of mercury above the capillary, and a constant-temperature bath. The cell may be of simple design; for example a test tube is 15 x 85 mm. This cell is fitted with a three-hole notched rubber stopper that will hold the dropping mercury electrode, the contact electrode for the anode (a pool of mercury), and a tube for flushing the solution with nitrogen. 2.1.3 Nitrogen cylinder and tubing. 2.1.4 Other apparatus: pipets, 5, 15, 20, and 50 mL; three 200 mL volumetric flasks. 2.2 Reagents. 2.2.1 Standard zinc solution (1 mL = 0.0010 g of Zn): Dissolve 1.245 g of freshly ignited ZnO in 50 mL of hot HCl (1:10). Cool, dilute with water to 1000 mL in a volumetric flask, and mix.

2.2.2 Standard cadmium solution (1 mL = 0.0010 g of Cd): Dissolve 1.631 g of anhydrous CdCl2 in 100 mL of hot water. Cool, dilute to 100 mL in a volumetric flask and mix. 2.2.3 Gelatin solution (2 g/1000 mL): Dissolve 2.00 g of gelatin in boiling water and dilute the clear solution to 1000 mL. 2.2.4 Nitrogen (with minimum oxygen content).

2.2.5 NH4Cl (crystalline). 2.2.6 HCl (12 N).

2.2.7 NH4OH (14.8 N).

2.2.8 HNO3 (15.7 N). 2.3 Sampling and test specimen. 2.3.1 From each test unit obtained in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product” (for paper) or TAPPI T 657 “Sampling of Fillers and Pigments” (for pigments), prepare a specimen sufficient to contain at least 10 mg of zinc or 10 mg of cadmium if present. 3 / Zinc and cadmium in paper T 438 cm-96

2.3.2 Normally about 1 g or less of dry paper is sufficient for a single determination; more is needed if its moisture content is unknown. 2.3.3 If the moisture content is unknown, determine it in accordance with TAPPI T 412 “Moisture in Paper and Paperboard.” 2.4 Procedure. 2.4.1 Detailed information regarding the polarographic procedure may be found in the literature (1-3). 2.4.2 Zinc and cadmium factors. 2.4.2.1 Transfer 20.0 and 50 mL aliquots of the standard zinc and cadmium solutions, respectively, to each of two 200 mL volumetric flasks. To each of these flasks, and to a third flask to be carried through the entire procedure as a blank, add 16.6 g of NH4Cl and 5 mL of HCl, and dilute to approximately 150 mL with water. Add 15 mL of NH4OH and 10 mL of gelatin solution. Cool, dilute to the mark with water, and mix. 2.4.2.2 Transfer suitable portions of the resulting solutions to electrolysis cells and remove oxygen by bubbling nitrogen through the solutions for 10 min.

NOTE 1: Since the diffusion current increases with increasing temperature, arrangement must be made to control standards and specimens at a uniform temperature during electrolysis or to make corrections for temperature fluctuations. Other conditions such as drop time and height of the mercury column must also be constant.

2.4.2.3 Determine the increase in the galvanometer deflection in divisions when changing from an applied potential of -0.58 to -0.83 V, and again when changing from -1.09 to -1.40 V for each solution. Adjust the sensitivity of the polarograph circuit so as to obtain optimum increases in galvanometer deflection.

NOTE 2: These voltage settings must be on the residual current plateaus and the diffusion current plateaus, respectively. Since the wave form may be affected by the sensitivity of the galvanometer, a complete polarogram should be plotted and the above settings checked for the particular instrument being used.

2.4.2.4 Multiply the increase in galvanometer deflection obtained by increasing the potential from -0.58 to -0.83 V for each solution by the shunt setting used and plot these values against the amount of cadmium in grams. Next multiply the increase in galvanometer deflection obtained by increasing the potential from -1.09 to -1.40 V for each solution by the shunt settings used and plot these values against the amount of zinc in grams. The three points must fall approximately on a straight line for both metals. T 438 cm-96 Zinc and cadmium in paper / 4

2.4.2.5 Calculate the cadmium and zinc factors as follows:

C1

F1 =

(R1 - B1)

C2

F2 =

(R2 - B2)

where

F1 = cadmium per galvanometer scale division at full sensitivity, gx.

C1 = cadmium in the standard, g.

R1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the standard.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank.

F2 = zinc per galvanometer scale division at full sensitivity, g.

C2 = zinc in the standard, g.

R2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the standard.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank.

NOTE 3: If conditions are kept constant, there is no need to redetermine the cadmium and zinc factors until a new capillary is used.

2.4.3 Analysis of specimen. Transfer about 0.5 g of the dried specimen, weighed to the nearest 0.001 g, to a

400 mL beaker. Add 10 mL of concentrated H2SO4 and heat to char the paper. Oxidize with HNO3 and, when the solution is clear, evaporate to dryness. Add 16.6 g of NH4Cl, 5 mL of HCl, and 50 mL of water. Heat until solution is complete. Cool, transfer to a 200 mL volumetric flask, and dilute to approximately 150 mL with water. Add 15 mL of

NH4OH and 1 mL of gelatin solution. Cool, dilute to 200 mL, and continue in accordance with the procedure for determining the zinc and cadmium factors. 2.4.4 Calculation. Calculate the percentage of cadmium and zinc as follows:

(A1 - B1) F1 Cadmium, % = x 100 W 5 / Zinc and cadmium in paper T 438 cm-96

(A2 - B2) F2 Zinc, % = x 100 W where

A1 = increase galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the specimen.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank, in accordance with the procedure.

F1 = cadmium per galvanometer scale division at full sensitivity, g. W = weight of specimen, g.

A2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the specimen.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank, in accordance with the procedure.

F2 = zinc per galvanometer scale division at full sensitivity, g.

3. Gravimetric and volumetric procedures

3.1 Apparatus. 3.1.1 For cadmium by the gravimetric procedure. 3.1.1.1 Platinum dish, evaporating about 50 mL. 3.1.1.2 Other apparatus: three 400 mL beakers; 25 and 50 mL graduated cylinders; filter funnel with fine filter paper. 3.1.2 For zinc by the volumetric procedure. As for cadmium and in addition: a 3 and a 5 mL pipet (or small graduated cylinder); medium filter paper; 50 mL buret. 3.2 Reagents. 3.2.1 For cadmium by the gravimetric procedure. 3.2.1.1 Sulfuric acid, concentrated; also dilute (1:1). 3.2.1.2 Nitric acid, concentrated.

3.2.1.3 Hydrogen sulfide, H2S (generator or cylinder). 3.2.1.4 Hydrochloric acid, dilute (3:7). 3.2.2 For zinc by the volumetric procedure. 3.2.2.1 As for cadmium, and in addition:

3.2.2.2 Uranyl acetate indicator. Dissolve 5 g of UO2(CH3COO2) - 2H2O in water, acidify with acetic acid, and dilute to 100 mL.

3.2.2.3 Ammonia, dilute NH4OH (1:1). 3.2.2.4 Hydrochloric acid, concentrated; also dilute (1:1). T 438 cm-96 Zinc and cadmium in paper / 6

3.2.2.5 Sulfuric acid, dilute (5:95). 3.2.2.6 Methyl orange indicator. 3.2.2.7 Zinc, metal, reagent grade. 3.2.2.8 Litmus paper.

3.2.2.9 Potassium ferrocyanide, standard solution 1 mL = 0.01 g of Zn): Dissolve 42.3 g of K4Fe(CN6) -3H2O in water and dilute to 1000 mL. To standardize, transfer 0.3200 - 0.3400 g of zinc to a 400 mL beaker, then dissolve in 10 mL of concentrated HCl and 20 mL of water. Add NH4OH until slightly alkaline to litmus paper; then add HCl until just

acid, plus 3 mL in excess. Dilute to about 250 mL with hot water and heat nearly to boiling. Titrate with K4Fe(CN6) solution, while stirring constantly, until a drop tested on a white porcelain plate with a drop of uranyl acetate indicator shows a brown tinge after standing 1 min. Make a blank determination following the same procedure and using the same

amounts of reagents and water. Calculate the zinc factor of the K4Fe(CN6) solution as follows:

F = Cl(A - B) where

F = zinc equivalent of K4Fe(CN6) solution, g/mL.

A = K4Fe(CN6) solution required to titrate the zinc solution, mL.

B = K4Fe(CN6) solution required to titrate the blank, mL. C = zinc used, g.

NOTE 4: Care should be taken in the handling of K4Fe(CN6) because atmosphere oxygen rapidly converts it to K3Fe(CN6).

3.3 Sampling and test specimen. 3.3.1 Sample as previously described for the polarographic procedure (2.3.1) except use a 4 g specimen for the analysis of zinc in zinc pigments. 3.3.2 Normally about 4 g or less of dry paper is sufficient for a single determination of zinc and cadmium in paper. 3.4 Procedures. 3.4.1 For cadmium by the gravimetric procedure. 3.4.1.1 Place about 4 g of the specimen in a tared weighing bottle, dry to constant weight and weigh to the nearest 5 mg. Transfer to a 400 mL beaker and add 20 mL of concentrated H2SO4. Heat to char the paper and add sufficient HNO3 to oxidize the mixture to a clear solution. Evaporate to dryness and add approximately 100 mL of water and 10 mL of 1:1 H2SO4. Heat to dissolve, and filter if there is any insoluble residue. Dilute to approximately 200 mL, and pass a rapid stream of H2S through the solution for 20 min. Filter through fme paper, but do not wash. Reserve the filtrate. 7 / Zinc and cadmium in paper T 438 cm-96

3.4.1.2 Dissolve the precipitate on the paper with cold 3:7 HCl and wash the paper well with water, catching the solution in the same 400 mL beaker. Add 15 mL of 1:1 H2SO4 and evaporate to dense white fumes. Cool, dilute to 200 mL, and reprecipitate as above. 3.4.1.3 Filter, using a fme paper. Combine the filtrate with that reserved above and reserve the combined filtrates for the determination of zinc. Dissolve the precipitate with cold 3:7 HCl followed by washing with water, receiving the solution in a weighed platinum dish. Add 10 mL of 1:1 H2SO4 and evaporate to dense white fumes.

Remove the excess H2SO4 by heating the dish cautiously, and finally heat to 500 - 600°C. Cool, and weigh as CdSO4. 3.4.1.4 Calculation. Calculate the percentage of cadmium as follows:

A x 0.5392 Cadmium, % = x 100 B where

A = weight of CdSO4, g. B = dry weight of specimen, g.

3.4.2 For zinc by the volumetric procedure. 3.4.2.1 Evaporate the combined filtrates, obtained in accordance with the gravimetric procedure for cadmium, to dryness. Add 5 mL of 1:1 H2SO4 and 100 mL of water, and heat to dissolve. Cool, and add 1:4 NH4OH until just

alkaline. Add 1:4 H2SO4 until neutral to methyl orange, and then add 3 mL of 5:95 H2SO4. Dilute to 200 mL and through a short glass tube, pass a rapid stream of H2S through the solution for 40 min. Leave the tube in the beaker and allow the precipitate to settle for 10 min. 3.4.2.2 Filter, using a medium paper, and wash twice with cold water. Discard filtrate. Place the original beaker and gassing tube under the funnel and punch a hole in the paper. Wash the bulk of the ZnS into the beaker, using hot water. Wash the paper with 40 mL of hot 1:4 HCl and again with hot water. Dissolve the zinc sulfide still adhering to the gassing tube with a minimum quantity of hot 1:4 HCl.

3.4.2.3 Boil to expel H2S. Cool, and add NH4OH until slightly alkaline to litmus paper; then add HCl until just acid, plus 3 mL in excess. Dilute to 250 mL with hot water and heat nearly to boiling. Titrate as described previously. 3.4.2.4 Calculation. Calculate the percentage of zinc in the specimen as follows:

(A - B) F Zn, % = x 100 C where

A = K4Fe(CN6) solution required to titrate the specimen, mL.

B = K4Fe(CN6) solution required to titrate the blanks as described under 3.2.2.9. (standardization of potassium ferrocyanide), mL. T 438 cm-96 Zinc and cadmium in paper / 8

F = zinc equivalent of the K4Fe(CN6) solution, g/mL. C = weight of specimen, g.

4. Atomic absorption procedure

4.1 Summary. A paper specimen is reacted with H2SO4 and H2O2. The resulting solution is diluted, and the concentrations of Zn and/or Cd are measured with a atomic absorption spectrophotometer. A calculation of the weight percents of Zn and/or Cd is then made. 4.2 Definition. Linear working range is that concentration range over which instrument response is propor- tional to concentration. 4.3 Apparatus. 4.3.1 Atomic absorption spectrophotometer. 4.3.2 Erlenmeyer flask, 250 mL with 24/40 ground glass opening. 4.3.3 Parallel side arm connector, 3-way, with 24/40 ground glass joint. 4.3.4 Graduated cylindrical funnel, 50 mL with 24/40 ground glass joint. 4.3.5 Hot plate. 4.3.6 Ring stand. 4.3.7 Analytical balance, capable of reading to 0.001 g. 4.3.8 Volumetric glassware, to include at least one of each of the following flasks, 500 mL, 250 mL, and 100 mL; pipets, 50 mL, 25 mL, 10 mL, and 1 mL. 4.4 Reagents and materials. 4.4.1 Stock Zn solution, 500 μg/mL. Prepare by dissolving 0.500 g of zinc metal in a minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl. 4.4.2 Stock Cd solution, 500 μg/mL. Prepare by dissolving 0.500 g of cadmium metal in minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl.

4.4.3 H2SO4, 98% wt./wt.

4.4.4 H2O2, 30% wt./wt. 4.5 Sampling and test specimens. 4.5.1 Obtain a sample in accordance with TAPPI T 400. 4.5.2 Obtain 1 to 2 g of specimen from various positions on each test unit in the form of small strips. 4.5.3 Dry composite test specimen for 1 h at 105°C and place in a desiccator at least 0.5 h before analyzing. 4.6 Procedure. 4.6.1 Weigh to the third decimal place, a specimen between 1 and 2 g. Add test specimen to a 250 mL

Erlenmeyer flask containing 5 mL of concentrated H2SO4. Attach 3-way parallel side arm connector and 50 mL

cylindrical funnel containing approximately 40 mL of 30% H2O2 to the flask. Support glassware with ring stand and place flask on hot plate. Heat the mixture until the specimen is completely charred and dense white fumes appear. Add

H2O2 at a rate of approximately 1 drop per second until a clear solution results. Evaporate the solution to dryness. Then 9 / Zinc and cadmium in paper T 438 cm-96

cool, add 20 mL HCl (1+1) and 50 mL of water and heat until solution is complete. Allow to cool, then transfer contents of the flask into a 1000 mL volumetric flask and dilute to the mark with water. 4.6.2 Prepare calibration standards by diluting stock zinc and cadmium solutions to 0.1, 0.5, and 1.0 g/mL with 1% (v/v) HCl. Set instrumental conditions according to manufacturer's specifications. Instrument operating conditions are given in 4.6.3. Use either absorbence or concentration readout mode depending on how instrument is equipped. Zero instrument with deionized H2O. Measure calibration standards or set concentration readout. Measure specimens in this sequence: specimen, standard, specimen. Make 3 readings on each specimen. If a specimen concentration readout or absorbence falls outside of the linear range suggested by manufacturer or established by experimentation, dilute solution to get response in linear working range. 4.6.3 Instrument operating conditions.

Analytical Light Flame Element (Slit) wavelength source type

Zinc 0.7 nm 213.9 nm Hollow Air- cathode acetylene lamp (lean) Cadmium 0.7 nm 228.8 nm Hollow Air- cathode acetylene lamp (lean)

4.6.4 Calculation. Calculate the percentages of Zn and/or Cd as follows:

AB Cd, % or Zn, % = (105) C where A = concentration of Zn and Cd, μg/mL. B = dilution factor; example: a 10 mL aliquot of solution is diluted to 100 mL; then dilution factor equals 10. C = weight of test specimen, μg.

T 438 cm-96 Zinc and cadmium in paper / 10

5. Report

5.1 Report the amount of zinc or cadmium as a percentage of the moisture-free material, to the nearest 0.1%, and state the procedure used. 5.2 For the atomic absorption procedure, results are to consist of a listing of the following: 5.2.1 Measured absorbances or concentrations. 5.2.2 A graph on which concentrations of Zn and Cd standards are plotted against their absorbences. 5.2.3 A statement of instrumental conditions to include lamp current, wavelength of measurement, type of flame, type of burner, and any special equipment used for the improvement of instrument performance. 5.2.4 A calculation of % Zn and/or Cd. 5.2.5 Notes on any observances of unusual behavior of either the instrument or the reaction.

6. Precision

6.1 Repeatability: all repeatability values are based on the amount present.

Material Method Repeatability

Zn (0-25%) Polarographic 1% Cd (0-25%) Polarographic 1% Zn (>25%) Volumetric 1% Cd Gravimetric 0.5% Zn (0-5%) Atomic absorption 2% Cd (0-5%) Atomic absorption 2%

6.2 Reproducibility: not known; 6.3 Comparability: not known, in accordance with definition of above terms used as defined in TAPPI T 1200 “Interlaboratory Evaluation of Test Methods to Determine TAPPI Repeatability and Reproducibility.”

7. Additional Information

7.1 Effective date of issue: to be assigned. 7.2 In the atomic absorption method, the extent of interferences from other ions has not been fully examined; however, the absorbances of Zn and Cd are not significantly affected by 10-fold excesses of each other. Ca in a 10-fold 11 / Zinc and cadmium in paper T 438 cm-96

excess depresses Zn absorbance slightly. Ti in a 10-fold excess seems to have no effect on Zn absorbance. Sulfuric acid enhances both absorbances. 7.2.1 Detection limits can be significantly improved by the use of a graphite tube furnace in the atomic absorption procedure. 7.2.2 The atomic absorption procedure can be applied to many other metal ions (5). 7.3 Related method: ASTM D-1224.

References

1. Kolthoff, I. M., and Ligane, J. J., Polarography, 2nd edn., Vol. 2, Interscience, New York, 1952. 2. Muller, O. H., “The Polarographic Method of Analysis,” J. Chem. Educ., Feb.-July, 1981. 3. Strong, C. L., “How to Build a Polarograph,” Scientific American 226 (9): 247 (1962). 4. Atomic Absorption Product Department, Perkin-Elmer Corp., Analytical Methods for Atomic Absorption Spectrophotometry, 1973. 5. Price, J. P., “Utilization of Atomic Absorption Spectroscopy in the Synthetic Fiber Industry,” Tappi 54 (9):1497 (1971).

Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Director of Quality and Standards. g

WI 050114.01

T 438

DRAFT NO. 3

DATE October 18, 2005 TAPPI WORKING GROUP CHAIRMAN J Ishley

SUBJECT CATEGORY Fillers & Pigments Testing

RELATED METHODS See “Additional Information”

CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals.

Zinc and cadmium in paper (Reaffirmation of T 438 cm-96)

(Lines in text or margins indicate changes since last draft)

1. Scope and significance

1.1 This method maybe used for the determination of cadmium and zinc either in paper or in highly opaque pigments. Zinc is usually present in zinc oxide, zinc sulfide, or as lithopone (a combination of zinc sulfide and barium sulfate), which is occasionally used in filled paper, in paper coatings and in high-pressure laminates and wallpaper. Some forms of zinc oxide have photoelectric properties and are found in certain papers used for photo reproduction. Zinc or cadmium pigments are sometimes added to papers to cause fluorescence, and zinc oxide has been used to enhance the cohesive strength of some types of paper coatings. 1.2 Three procedures for each element are described: polarographic, either gravimetric or volumetric, and atomic absorption. The gravimetric procedure is suitable if a polarograph is not available. For the determination of zinc in a zinc-bearing pigment, the volumetric procedure is recommended, because the polarographic procedure is insensitive

Approved by the Standard Specific Interest Group for this Test Method TAPPI T 438 cm-96 Zinc and cadmium in paper / 2

over 25% Zn levels. The polarographic procedure can be used for the determination of zinc and cadmium in paper and for cadmium in cadmium bearing pigments. The preferred procedure for each material is based on its concentration. 1.3 When zinc is to be determined volumetrically (cadmium absent) one precipitation of heavy metals with washing is sufficient. 1.4 In the atomic absorption procedure, sensitivities for 1% absorption are 0.02 mg/mL Zn and 0.03 mg/mL Cd, respectively. The repeatability of this procedure is questionable at present for Zn and Cd concentrations of greater than 5%.

2. Polarographic procedure

2.1 Apparatus. 2.1.1 Polarograph, of the manually operated type. A recording polarograph may be used, although this method is written specifically for a manually operated instrument. 2.1.2 Electrolysis equipment, including a cell, a dropping mercury electrode, an arrangement for maintaining a constant head of mercury above the capillary, and a constant-temperature bath. The cell may be of simple design; for example a test tube is 15 x 85 mm. This cell is fitted with a three-hole notched rubber stopper that will hold the dropping mercury electrode, the contact electrode for the anode (a pool of mercury), and a tube for flushing the solution with nitrogen. 2.1.3 Nitrogen cylinder and tubing. 2.1.4 Other apparatus: pipets, 5, 15, 20, and 50 mL; three 200 mL volumetric flasks. 2.2 Reagents. 2.2.1 Standard zinc solution (1 mL = 0.0010 g of Zn): Dissolve 1.245 g of freshly ignited ZnO in 50 mL of hot HCl (1:10). Cool, dilute with water to 1000 mL in a volumetric flask, and mix.

2.2.2 Standard cadmium solution (1 mL = 0.0010 g of Cd): Dissolve 1.631 g of anhydrous CdCl2 in 100 mL of hot water. Cool, dilute to 100 mL in a volumetric flask and mix. 2.2.3 Gelatin solution (2 g/1000 mL): Dissolve 2.00 g of gelatin in boiling water and dilute the clear solution to 1000 mL. 2.2.4 Nitrogen (with minimum oxygen content).

2.2.5 NH4Cl (crystalline). 2.2.6 HCl (12 N).

2.2.7 NH4OH (14.8 N).

2.2.8 HNO3 (15.7 N). 2.3 Sampling and test specimen. 2.3.1 From each test unit obtained in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product” (for paper) or TAPPI T 657 “Sampling of Fillers and Pigments” (for pigments), prepare a specimen sufficient to contain at least 10 mg of zinc or 10 mg of cadmium if present. 3 / Zinc and cadmium in paper T 438 cm-96

2.3.2 Normally about 1 g or less of dry paper is sufficient for a single determination; more is needed if its moisture content is unknown. 2.3.3 If the moisture content is unknown, determine it in accordance with TAPPI T 412 “Moisture in Paper and Paperboard.” 2.4 Procedure. 2.4.1 Detailed information regarding the polarographic procedure may be found in the literature (1-3). 2.4.2 Zinc and cadmium factors. 2.4.2.1 Transfer 20.0 and 50 mL aliquots of the standard zinc and cadmium solutions, respectively, to each of two 200 mL volumetric flasks. To each of these flasks, and to a third flask to be carried through the entire procedure as a blank, add 16.6 g of NH4Cl and 5 mL of HCl, and dilute to approximately 150 mL with water. Add 15 mL of NH4OH and 10 mL of gelatin solution. Cool, dilute to the mark with water, and mix. 2.4.2.2 Transfer suitable portions of the resulting solutions to electrolysis cells and remove oxygen by bubbling nitrogen through the solutions for 10 min.

NOTE 1: Since the diffusion current increases with increasing temperature, arrangement must be made to control standards and specimens at a uniform temperature during electrolysis or to make corrections for temperature fluctuations. Other conditions such as drop time and height of the mercury column must also be constant.

2.4.2.3 Determine the increase in the galvanometer deflection in divisions when changing from an applied potential of -0.58 to -0.83 V, and again when changing from -1.09 to -1.40 V for each solution. Adjust the sensitivity of the polarograph circuit so as to obtain optimum increases in galvanometer deflection.

NOTE 2: These voltage settings must be on the residual current plateaus and the diffusion current plateaus, respectively. Since the wave form may be affected by the sensitivity of the galvanometer, a complete polarogram should be plotted and the above settings checked for the particular instrument being used.

2.4.2.4 Multiply the increase in galvanometer deflection obtained by increasing the potential from -0.58 to -0.83 V for each solution by the shunt setting used and plot these values against the amount of cadmium in grams. Next multiply the increase in galvanometer deflection obtained by increasing the potential from -1.09 to -1.40 V for each solution by the shunt settings used and plot these values against the amount of zinc in grams. The three points must fall approximately on a straight line for both metals. T 438 cm-96 Zinc and cadmium in paper / 4

2.4.2.5 Calculate the cadmium and zinc factors as follows:

C1

F1 =

(R1 - B1)

C2

F2 =

(R2 - B2)

where

F1 = cadmium per galvanometer scale division at full sensitivity, gx.

C1 = cadmium in the standard, g.

R1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the standard.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank.

F2 = zinc per galvanometer scale division at full sensitivity, g.

C2 = zinc in the standard, g.

R2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the standard.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank.

NOTE 3: If conditions are kept constant, there is no need to redetermine the cadmium and zinc factors until a new capillary is used.

2.4.3 Analysis of specimen. Transfer about 0.5 g of the dried specimen, weighed to the nearest 0.001 g, to a

400 mL beaker. Add 10 mL of concentrated H2SO4 and heat to char the paper. Oxidize with HNO3 and, when the solution is clear, evaporate to dryness. Add 16.6 g of NH4Cl, 5 mL of HCl, and 50 mL of water. Heat until solution is complete. Cool, transfer to a 200 mL volumetric flask, and dilute to approximately 150 mL with water. Add 15 mL of

NH4OH and 1 mL of gelatin solution. Cool, dilute to 200 mL, and continue in accordance with the procedure for determining the zinc and cadmium factors. 2.4.4 Calculation. Calculate the percentage of cadmium and zinc as follows:

(A1 - B1) F1 Cadmium, % = x 100 W 5 / Zinc and cadmium in paper T 438 cm-96

(A2 - B2) F2 Zinc, % = x 100 W where

A1 = increase galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the specimen.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank, in accordance with the procedure.

F1 = cadmium per galvanometer scale division at full sensitivity, g. W = weight of specimen, g.

A2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the specimen.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank, in accordance with the procedure.

F2 = zinc per galvanometer scale division at full sensitivity, g.

3. Gravimetric and volumetric procedures

3.1 Apparatus. 3.1.1 For cadmium by the gravimetric procedure. 3.1.1.1 Platinum dish, evaporating about 50 mL. 3.1.1.2 Other apparatus: three 400 mL beakers; 25 and 50 mL graduated cylinders; filter funnel with fine filter paper. 3.1.2 For zinc by the volumetric procedure. As for cadmium and in addition: a 3 and a 5 mL pipet (or small graduated cylinder); medium filter paper; 50 mL buret. 3.2 Reagents. 3.2.1 For cadmium by the gravimetric procedure. 3.2.1.1 Sulfuric acid, concentrated; also dilute (1:1). 3.2.1.2 Nitric acid, concentrated.

3.2.1.3 Hydrogen sulfide, H2S (generator or cylinder). 3.2.1.4 Hydrochloric acid, dilute (3:7). 3.2.2 For zinc by the volumetric procedure. 3.2.2.1 As for cadmium, and in addition:

3.2.2.2 Uranyl acetate indicator. Dissolve 5 g of UO2(CH3COO2) - 2H2O in water, acidify with acetic acid, and dilute to 100 mL.

3.2.2.3 Ammonia, dilute NH4OH (1:1). 3.2.2.4 Hydrochloric acid, concentrated; also dilute (1:1). T 438 cm-96 Zinc and cadmium in paper / 6

3.2.2.5 Sulfuric acid, dilute (5:95). 3.2.2.6 Methyl orange indicator. 3.2.2.7 Zinc, metal, reagent grade. 3.2.2.8 Litmus paper.

3.2.2.9 Potassium ferrocyanide, standard solution 1 mL = 0.01 g of Zn): Dissolve 42.3 g of K4Fe(CN6) -3H2O in water and dilute to 1000 mL. To standardize, transfer 0.3200 - 0.3400 g of zinc to a 400 mL beaker, then dissolve in 10 mL of concentrated HCl and 20 mL of water. Add NH4OH until slightly alkaline to litmus paper; then add HCl until just

acid, plus 3 mL in excess. Dilute to about 250 mL with hot water and heat nearly to boiling. Titrate with K4Fe(CN6) solution, while stirring constantly, until a drop tested on a white porcelain plate with a drop of uranyl acetate indicator shows a brown tinge after standing 1 min. Make a blank determination following the same procedure and using the same

amounts of reagents and water. Calculate the zinc factor of the K4Fe(CN6) solution as follows:

F = Cl(A - B) where

F = zinc equivalent of K4Fe(CN6) solution, g/mL.

A = K4Fe(CN6) solution required to titrate the zinc solution, mL.

B = K4Fe(CN6) solution required to titrate the blank, mL. C = zinc used, g.

NOTE 4: Care should be taken in the handling of K4Fe(CN6) because atmosphere oxygen rapidly converts it to K3Fe(CN6).

3.3 Sampling and test specimen. 3.3.1 Sample as previously described for the polarographic procedure (2.3.1) except use a 4 g specimen for the analysis of zinc in zinc pigments. 3.3.2 Normally about 4 g or less of dry paper is sufficient for a single determination of zinc and cadmium in paper. 3.4 Procedures. 3.4.1 For cadmium by the gravimetric procedure. 3.4.1.1 Place about 4 g of the specimen in a tared weighing bottle, dry to constant weight and weigh to the nearest 5 mg. Transfer to a 400 mL beaker and add 20 mL of concentrated H2SO4. Heat to char the paper and add sufficient HNO3 to oxidize the mixture to a clear solution. Evaporate to dryness and add approximately 100 mL of water and 10 mL of 1:1 H2SO4. Heat to dissolve, and filter if there is any insoluble residue. Dilute to approximately 200 mL, and pass a rapid stream of H2S through the solution for 20 min. Filter through fme paper, but do not wash. Reserve the filtrate. 7 / Zinc and cadmium in paper T 438 cm-96

3.4.1.2 Dissolve the precipitate on the paper with cold 3:7 HCl and wash the paper well with water, catching the solution in the same 400 mL beaker. Add 15 mL of 1:1 H2SO4 and evaporate to dense white fumes. Cool, dilute to 200 mL, and reprecipitate as above. 3.4.1.3 Filter, using a fme paper. Combine the filtrate with that reserved above and reserve the combined filtrates for the determination of zinc. Dissolve the precipitate with cold 3:7 HCl followed by washing with water, receiving the solution in a weighed platinum dish. Add 10 mL of 1:1 H2SO4 and evaporate to dense white fumes.

Remove the excess H2SO4 by heating the dish cautiously, and finally heat to 500 - 600°C. Cool, and weigh as CdSO4. 3.4.1.4 Calculation. Calculate the percentage of cadmium as follows:

A x 0.5392 Cadmium, % = x 100 B where

A = weight of CdSO4, g. B = dry weight of specimen, g.

3.4.2 For zinc by the volumetric procedure. 3.4.2.1 Evaporate the combined filtrates, obtained in accordance with the gravimetric procedure for cadmium, to dryness. Add 5 mL of 1:1 H2SO4 and 100 mL of water, and heat to dissolve. Cool, and add 1:4 NH4OH until just

alkaline. Add 1:4 H2SO4 until neutral to methyl orange, and then add 3 mL of 5:95 H2SO4. Dilute to 200 mL and through a short glass tube, pass a rapid stream of H2S through the solution for 40 min. Leave the tube in the beaker and allow the precipitate to settle for 10 min. 3.4.2.2 Filter, using a medium paper, and wash twice with cold water. Discard filtrate. Place the original beaker and gassing tube under the funnel and punch a hole in the paper. Wash the bulk of the ZnS into the beaker, using hot water. Wash the paper with 40 mL of hot 1:4 HCl and again with hot water. Dissolve the zinc sulfide still adhering to the gassing tube with a minimum quantity of hot 1:4 HCl.

3.4.2.3 Boil to expel H2S. Cool, and add NH4OH until slightly alkaline to litmus paper; then add HCl until just acid, plus 3 mL in excess. Dilute to 250 mL with hot water and heat nearly to boiling. Titrate as described previously. 3.4.2.4 Calculation. Calculate the percentage of zinc in the specimen as follows:

(A - B) F Zn, % = x 100 C where

A = K4Fe(CN6) solution required to titrate the specimen, mL.

B = K4Fe(CN6) solution required to titrate the blanks as described under 3.2.2.9. (standardization of potassium ferrocyanide), mL. T 438 cm-96 Zinc and cadmium in paper / 8

F = zinc equivalent of the K4Fe(CN6) solution, g/mL. C = weight of specimen, g.

4. Atomic absorption procedure

4.1 Summary. A paper specimen is reacted with H2SO4 and H2O2. The resulting solution is diluted, and the concentrations of Zn and/or Cd are measured with a atomic absorption spectrophotometer. A calculation of the weight percents of Zn and/or Cd is then made. 4.2 Definition. Linear working range is that concentration range over which instrument response is propor- tional to concentration. 4.3 Apparatus. 4.3.1 Atomic absorption spectrophotometer. 4.3.2 Erlenmeyer flask, 250 mL with 24/40 ground glass opening. 4.3.3 Parallel side arm connector, 3-way, with 24/40 ground glass joint. 4.3.4 Graduated cylindrical funnel, 50 mL with 24/40 ground glass joint. 4.3.5 Hot plate. 4.3.6 Ring stand. 4.3.7 Analytical balance, capable of reading to 0.001 g. 4.3.8 Volumetric glassware, to include at least one of each of the following flasks, 500 mL, 250 mL, and 100 mL; pipets, 50 mL, 25 mL, 10 mL, and 1 mL. 4.4 Reagents and materials. 4.4.1 Stock Zn solution, 500 μg/mL. Prepare by dissolving 0.500 g of zinc metal in a minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl. 4.4.2 Stock Cd solution, 500 μg/mL. Prepare by dissolving 0.500 g of cadmium metal in minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl.

4.4.3 H2SO4, 98% wt./wt.

4.4.4 H2O2, 30% wt./wt. 4.5 Sampling and test specimens. 4.5.1 Obtain a sample in accordance with TAPPI T 400. 4.5.2 Obtain 1 to 2 g of specimen from various positions on each test unit in the form of small strips. 4.5.3 Dry composite test specimen for 1 h at 105°C and place in a desiccator at least 0.5 h before analyzing. 4.6 Procedure. 4.6.1 Weigh to the third decimal place, a specimen between 1 and 2 g. Add test specimen to a 250 mL

Erlenmeyer flask containing 5 mL of concentrated H2SO4. Attach 3-way parallel side arm connector and 50 mL

cylindrical funnel containing approximately 40 mL of 30% H2O2 to the flask. Support glassware with ring stand and place flask on hot plate. Heat the mixture until the specimen is completely charred and dense white fumes appear. Add

H2O2 at a rate of approximately 1 drop per second until a clear solution results. Evaporate the solution to dryness. Then 9 / Zinc and cadmium in paper T 438 cm-96

cool, add 20 mL HCl (1+1) and 50 mL of water and heat until solution is complete. Allow to cool, then transfer contents of the flask into a 1000 mL volumetric flask and dilute to the mark with water. 4.6.2 Prepare calibration standards by diluting stock zinc and cadmium solutions to 0.1, 0.5, and 1.0 g/mL with 1% (v/v) HCl. Set instrumental conditions according to manufacturer's specifications. Instrument operating conditions are given in 4.6.3. Use either absorbence or concentration readout mode depending on how instrument is equipped. Zero instrument with deionized H2O. Measure calibration standards or set concentration readout. Measure specimens in this sequence: specimen, standard, specimen. Make 3 readings on each specimen. If a specimen concentration readout or absorbence falls outside of the linear range suggested by manufacturer or established by experimentation, dilute solution to get response in linear working range. 4.6.3 Instrument operating conditions.

Analytical Light Flame Element (Slit) wavelength source type

Zinc 0.7 nm 213.9 nm Hollow Air- cathode acetylene lamp (lean) Cadmium 0.7 nm 228.8 nm Hollow Air- cathode acetylene lamp (lean)

4.6.4 Calculation. Calculate the percentages of Zn and/or Cd as follows:

AB Cd, % or Zn, % = (105) C where A = concentration of Zn and Cd, μg/mL. B = dilution factor; example: a 10 mL aliquot of solution is diluted to 100 mL; then dilution factor equals 10. C = weight of test specimen, μg.

T 438 cm-96 Zinc and cadmium in paper / 10

5. Report

5.1 Report the amount of zinc or cadmium as a percentage of the moisture-free material, to the nearest 0.1%, and state the procedure used. 5.2 For the atomic absorption procedure, results are to consist of a listing of the following: 5.2.1 Measured absorbances or concentrations. 5.2.2 A graph on which concentrations of Zn and Cd standards are plotted against their absorbences. 5.2.3 A statement of instrumental conditions to include lamp current, wavelength of measurement, type of flame, type of burner, and any special equipment used for the improvement of instrument performance. 5.2.4 A calculation of % Zn and/or Cd. 5.2.5 Notes on any observances of unusual behavior of either the instrument or the reaction.

6. Precision

6.1 Repeatability: all repeatability values are based on the amount present.

Material Method Repeatability

Zn (0-25%) Polarographic 1% Cd (0-25%) Polarographic 1% Zn (>25%) Volumetric 1% Cd Gravimetric 0.5% Zn (0-5%) Atomic absorption 2% Cd (0-5%) Atomic absorption 2%

6.2 Reproducibility: not known; 6.3 Comparability: not known, in accordance with definition of above terms used as defined in TAPPI T 1200 “Interlaboratory Evaluation of Test Methods to Determine TAPPI Repeatability and Reproducibility.”

7. Additional Information

7.1 Effective date of issue: to be assigned. 7.2 In the atomic absorption method, the extent of interferences from other ions has not been fully examined; however, the absorbances of Zn and Cd are not significantly affected by 10-fold excesses of each other. Ca in a 10-fold 11 / Zinc and cadmium in paper T 438 cm-96

excess depresses Zn absorbance slightly. Ti in a 10-fold excess seems to have no effect on Zn absorbance. Sulfuric acid enhances both absorbances. 7.2.1 Detection limits can be significantly improved by the use of a graphite tube furnace in the atomic absorption procedure. 7.2.2 The atomic absorption procedure can be applied to many other metal ions (5). 7.3 Related method: ASTM D-1224.

References

1. Kolthoff, I. M., and Ligane, J. J., Polarography, 2nd edn., Vol. 2, Interscience, New York, 1952. 2. Muller, O. H., “The Polarographic Method of Analysis,” J. Chem. Educ., Feb.-July, 1981. 3. Strong, C. L., “How to Build a Polarograph,” Scientific American 226 (9): 247 (1962). 4. Atomic Absorption Product Department, Perkin-Elmer Corp., Analytical Methods for Atomic Absorption Spectrophotometry, 1973. 5. Price, J. P., “Utilization of Atomic Absorption Spectroscopy in the Synthetic Fiber Industry,” Tappi 54 (9):1497 (1971).

Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Director of Quality and Standards. g

WI 050114.01

T 438

DRAFT NO. 2

DATE July 5, 2005 TAPPI WORKING GROUP CHAIRMAN J Ishley

SUBJECT CATEGORY Fillers & Pigments Testing

RELATED METHODS See “Additional Information”

CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals.

Zinc and cadmium in paper (Reaffirmation of T 438 cm-96)

(Lines in text or margins indicate changes since last draft)

1. Scope and significance

1.1 This method maybe used for the determination of cadmium and zinc either in paper or in highly opaque pigments. Zinc is usually present in zinc oxide, zinc sulfide, or as lithopone (a combination of zinc sulfide and barium sulfate), which is occasionally used in filled paper, in paper coatings and in high-pressure laminates and wallpaper. Some forms of zinc oxide have photoelectric properties and are found in certain papers used for photo reproduction. Zinc or cadmium pigments are sometimes added to papers to cause fluorescence, and zinc oxide has been used to enhance the cohesive strength of some types of paper coatings. 1.2 Three procedures for each element are described: polarographic, either gravimetric or volumetric, and atomic absorption. The gravimetric procedure is suitable if a polarograph is not available. For the determination of zinc in a zinc-bearing pigment, the volumetric procedure is recommended, because the polarographic procedure is insensitive

Approved by the Standard Specific Interest Group for this Test Method TAPPI T 438 cm-96 Zinc and cadmium in paper / 2

over 25% Zn levels. The polarographic procedure can be used for the determination of zinc and cadmium in paper and for cadmium in cadmium bearing pigments. The preferred procedure for each material is based on its concentration. 1.3 When zinc is to be determined volumetrically (cadmium absent) one precipitation of heavy metals with washing is sufficient. 1.4 In the atomic absorption procedure, sensitivities for 1% absorption are 0.02 mg/mL Zn and 0.03 mg/mL Cd, respectively. The repeatability of this procedure is questionable at present for Zn and Cd concentrations of greater than 5%.

2. Polarographic procedure

2.1 Apparatus. 2.1.1 Polarograph, of the manually operated type. A recording polarograph may be used, although this method is written specifically for a manually operated instrument. 2.1.2 Electrolysis equipment, including a cell, a dropping mercury electrode, an arrangement for maintaining a constant head of mercury above the capillary, and a constant-temperature bath. The cell may be of simple design; for example a test tube is 15 x 85 mm. This cell is fitted with a three-hole notched rubber stopper that will hold the dropping mercury electrode, the contact electrode for the anode (a pool of mercury), and a tube for flushing the solution with nitrogen. 2.1.3 Nitrogen cylinder and tubing. 2.1.4 Other apparatus: pipets, 5, 15, 20, and 50 mL; three 200 mL volumetric flasks. 2.2 Reagents. 2.2.1 Standard zinc solution (1 mL = 0.0010 g of Zn): Dissolve 1.245 g of freshly ignited ZnO in 50 mL of hot HCl (1:10). Cool, dilute with water to 1000 mL in a volumetric flask, and mix.

2.2.2 Standard cadmium solution (1 mL = 0.0010 g of Cd): Dissolve 1.631 g of anhydrous CdCl2 in 100 mL of hot water. Cool, dilute to 100 mL in a volumetric flask and mix. 2.2.3 Gelatin solution (2 g/1000 mL): Dissolve 2.00 g of gelatin in boiling water and dilute the clear solution to 1000 mL. 2.2.4 Nitrogen (with minimum oxygen content).

2.2.5 NH4Cl (crystalline). 2.2.6 HCl (12 N).

2.2.7 NH4OH (14.8 N).

2.2.8 HNO3 (15.7 N). 2.3 Sampling and test specimen. 2.3.1 From each test unit obtained in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product” (for paper) or TAPPI T 657 “Sampling of Fillers and Pigments” (for pigments), prepare a specimen sufficient to contain at least 10 mg of zinc or 10 mg of cadmium if present. 3 / Zinc and cadmium in paper T 438 cm-96

2.3.2 Normally about 1 g or less of dry paper is sufficient for a single determination; more is needed if its moisture content is unknown. 2.3.3 If the moisture content is unknown, determine it in accordance with TAPPI T 412 “Moisture in Paper and Paperboard.” 2.4 Procedure. 2.4.1 Detailed information regarding the polarographic procedure may be found in the literature (1-3). 2.4.2 Zinc and cadmium factors. 2.4.2.1 Transfer 20.0 and 50 mL aliquots of the standard zinc and cadmium solutions, respectively, to each of two 200 mL volumetric flasks. To each of these flasks, and to a third flask to be carried through the entire procedure as a blank, add 16.6 g of NH4Cl and 5 mL of HCl, and dilute to approximately 150 mL with water. Add 15 mL of NH4OH and 10 mL of gelatin solution. Cool, dilute to the mark with water, and mix. 2.4.2.2 Transfer suitable portions of the resulting solutions to electrolysis cells and remove oxygen by bubbling nitrogen through the solutions for 10 min.

NOTE 1: Since the diffusion current increases with increasing temperature, arrangement must be made to control standards and specimens at a uniform temperature during electrolysis or to make corrections for temperature fluctuations. Other conditions such as drop time and height of the mercury column must also be constant.

2.4.2.3 Determine the increase in the galvanometer deflection in divisions when changing from an applied potential of -0.58 to -0.83 V, and again when changing from -1.09 to -1.40 V for each solution. Adjust the sensitivity of the polarograph circuit so as to obtain optimum increases in galvanometer deflection.

NOTE 2: These voltage settings must be on the residual current plateaus and the diffusion current plateaus, respectively. Since the wave form may be affected by the sensitivity of the galvanometer, a complete polarogram should be plotted and the above settings checked for the particular instrument being used.

2.4.2.4 Multiply the increase in galvanometer deflection obtained by increasing the potential from -0.58 to -0.83 V for each solution by the shunt setting used and plot these values against the amount of cadmium in grams. Next multiply the increase in galvanometer deflection obtained by increasing the potential from -1.09 to -1.40 V for each solution by the shunt settings used and plot these values against the amount of zinc in grams. The three points must fall approximately on a straight line for both metals. T 438 cm-96 Zinc and cadmium in paper / 4

2.4.2.5 Calculate the cadmium and zinc factors as follows:

C1

F1 =

(R1 - B1)

C2

F2 =

(R2 - B2)

where

F1 = cadmium per galvanometer scale division at full sensitivity, gx.

C1 = cadmium in the standard, g.

R1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the standard.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank.

F2 = zinc per galvanometer scale division at full sensitivity, g.

C2 = zinc in the standard, g.

R2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the standard.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank.

NOTE 3: If conditions are kept constant, there is no need to redetermine the cadmium and zinc factors until a new capillary is used.

2.4.3 Analysis of specimen. Transfer about 0.5 g of the dried specimen, weighed to the nearest 0.001 g, to a

400 mL beaker. Add 10 mL of concentrated H2SO4 and heat to char the paper. Oxidize with HNO3 and, when the solution is clear, evaporate to dryness. Add 16.6 g of NH4Cl, 5 mL of HCl, and 50 mL of water. Heat until solution is complete. Cool, transfer to a 200 mL volumetric flask, and dilute to approximately 150 mL with water. Add 15 mL of

NH4OH and 1 mL of gelatin solution. Cool, dilute to 200 mL, and continue in accordance with the procedure for determining the zinc and cadmium factors. 2.4.4 Calculation. Calculate the percentage of cadmium and zinc as follows:

(A1 - B1) F1 Cadmium, % = x 100 W 5 / Zinc and cadmium in paper T 438 cm-96

(A2 - B2) F2 Zinc, % = x 100 W where

A1 = increase galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the specimen.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank, in accordance with the procedure.

F1 = cadmium per galvanometer scale division at full sensitivity, g. W = weight of specimen, g.

A2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the specimen.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank, in accordance with the procedure.

F2 = zinc per galvanometer scale division at full sensitivity, g.

3. Gravimetric and volumetric procedures

3.1 Apparatus. 3.1.1 For cadmium by the gravimetric procedure. 3.1.1.1 Platinum dish, evaporating about 50 mL. 3.1.1.2 Other apparatus: three 400 mL beakers; 25 and 50 mL graduated cylinders; filter funnel with fine filter paper. 3.1.2 For zinc by the volumetric procedure. As for cadmium and in addition: a 3 and a 5 mL pipet (or small graduated cylinder); medium filter paper; 50 mL buret. 3.2 Reagents. 3.2.1 For cadmium by the gravimetric procedure. 3.2.1.1 Sulfuric acid, concentrated; also dilute (1:1). 3.2.1.2 Nitric acid, concentrated.

3.2.1.3 Hydrogen sulfide, H2S (generator or cylinder). 3.2.1.4 Hydrochloric acid, dilute (3:7). 3.2.2 For zinc by the volumetric procedure. 3.2.2.1 As for cadmium, and in addition:

3.2.2.2 Uranyl acetate indicator. Dissolve 5 g of UO2(CH3COO2) - 2H2O in water, acidify with acetic acid, and dilute to 100 mL.

3.2.2.3 Ammonia, dilute NH4OH (1:1). 3.2.2.4 Hydrochloric acid, concentrated; also dilute (1:1). T 438 cm-96 Zinc and cadmium in paper / 6

3.2.2.5 Sulfuric acid, dilute (5:95). 3.2.2.6 Methyl orange indicator. 3.2.2.7 Zinc, metal, reagent grade. 3.2.2.8 Litmus paper.

3.2.2.9 Potassium ferrocyanide, standard solution 1 mL = 0.01 g of Zn): Dissolve 42.3 g of K4Fe(CN6) -3H2O in water and dilute to 1000 mL. To standardize, transfer 0.3200 - 0.3400 g of zinc to a 400 mL beaker, then dissolve in 10 mL of concentrated HCl and 20 mL of water. Add NH4OH until slightly alkaline to litmus paper; then add HCl until just

acid, plus 3 mL in excess. Dilute to about 250 mL with hot water and heat nearly to boiling. Titrate with K4Fe(CN6) solution, while stirring constantly, until a drop tested on a white porcelain plate with a drop of uranyl acetate indicator shows a brown tinge after standing 1 min. Make a blank determination following the same procedure and using the same

amounts of reagents and water. Calculate the zinc factor of the K4Fe(CN6) solution as follows:

F = Cl(A - B) where

F = zinc equivalent of K4Fe(CN6) solution, g/mL.

A = K4Fe(CN6) solution required to titrate the zinc solution, mL.

B = K4Fe(CN6) solution required to titrate the blank, mL. C = zinc used, g.

NOTE 4: Care should be taken in the handling of K4Fe(CN6) because atmosphere oxygen rapidly converts it to K3Fe(CN6).

3.3 Sampling and test specimen. 3.3.1 Sample as previously described for the polarographic procedure (2.3.1) except use a 4 g specimen for the analysis of zinc in zinc pigments. 3.3.2 Normally about 4 g or less of dry paper is sufficient for a single determination of zinc and cadmium in paper. 3.4 Procedures. 3.4.1 For cadmium by the gravimetric procedure. 3.4.1.1 Place about 4 g of the specimen in a tared weighing bottle, dry to constant weight and weigh to the nearest 5 mg. Transfer to a 400 mL beaker and add 20 mL of concentrated H2SO4. Heat to char the paper and add sufficient HNO3 to oxidize the mixture to a clear solution. Evaporate to dryness and add approximately 100 mL of water and 10 mL of 1:1 H2SO4. Heat to dissolve, and filter if there is any insoluble residue. Dilute to approximately 200 mL, and pass a rapid stream of H2S through the solution for 20 min. Filter through fme paper, but do not wash. Reserve the filtrate. 7 / Zinc and cadmium in paper T 438 cm-96

3.4.1.2 Dissolve the precipitate on the paper with cold 3:7 HCl and wash the paper well with water, catching the solution in the same 400 mL beaker. Add 15 mL of 1:1 H2SO4 and evaporate to dense white fumes. Cool, dilute to 200 mL, and reprecipitate as above. 3.4.1.3 Filter, using a fme paper. Combine the filtrate with that reserved above and reserve the combined filtrates for the determination of zinc. Dissolve the precipitate with cold 3:7 HCl followed by washing with water, receiving the solution in a weighed platinum dish. Add 10 mL of 1:1 H2SO4 and evaporate to dense white fumes.

Remove the excess H2SO4 by heating the dish cautiously, and finally heat to 500 - 600°C. Cool, and weigh as CdSO4. 3.4.1.4 Calculation. Calculate the percentage of cadmium as follows:

A x 0.5392 Cadmium, % = x 100 B where

A = weight of CdSO4, g. B = dry weight of specimen, g.

3.4.2 For zinc by the volumetric procedure. 3.4.2.1 Evaporate the combined filtrates, obtained in accordance with the gravimetric procedure for cadmium, to dryness. Add 5 mL of 1:1 H2SO4 and 100 mL of water, and heat to dissolve. Cool, and add 1:4 NH4OH until just

alkaline. Add 1:4 H2SO4 until neutral to methyl orange, and then add 3 mL of 5:95 H2SO4. Dilute to 200 mL and through a short glass tube, pass a rapid stream of H2S through the solution for 40 min. Leave the tube in the beaker and allow the precipitate to settle for 10 min. 3.4.2.2 Filter, using a medium paper, and wash twice with cold water. Discard filtrate. Place the original beaker and gassing tube under the funnel and punch a hole in the paper. Wash the bulk of the ZnS into the beaker, using hot water. Wash the paper with 40 mL of hot 1:4 HCl and again with hot water. Dissolve the zinc sulfide still adhering to the gassing tube with a minimum quantity of hot 1:4 HCl.

3.4.2.3 Boil to expel H2S. Cool, and add NH4OH until slightly alkaline to litmus paper; then add HCl until just acid, plus 3 mL in excess. Dilute to 250 mL with hot water and heat nearly to boiling. Titrate as described previously. 3.4.2.4 Calculation. Calculate the percentage of zinc in the specimen as follows:

(A - B) F Zn, % = x 100 C where

A = K4Fe(CN6) solution required to titrate the specimen, mL.

B = K4Fe(CN6) solution required to titrate the blanks as described under 3.2.2.9. (standardization of potassium ferrocyanide), mL. T 438 cm-96 Zinc and cadmium in paper / 8

F = zinc equivalent of the K4Fe(CN6) solution, g/mL. C = weight of specimen, g.

4. Atomic absorption procedure

4.1 Summary. A paper specimen is reacted with H2SO4 and H2O2. The resulting solution is diluted, and the concentrations of Zn and/or Cd are measured with a atomic absorption spectrophotometer. A calculation of the weight percents of Zn and/or Cd is then made. 4.2 Definition. Linear working range is that concentration range over which instrument response is propor- tional to concentration. 4.3 Apparatus. 4.3.1 Atomic absorption spectrophotometer. 4.3.2 Erlenmeyer flask, 250 mL with 24/40 ground glass opening. 4.3.3 Parallel side arm connector, 3-way, with 24/40 ground glass joint. 4.3.4 Graduated cylindrical funnel, 50 mL with 24/40 ground glass joint. 4.3.5 Hot plate. 4.3.6 Ring stand. 4.3.7 Analytical balance, capable of reading to 0.001 g. 4.3.8 Volumetric glassware, to include at least one of each of the following flasks, 500 mL, 250 mL, and 100 mL; pipets, 50 mL, 25 mL, 10 mL, and 1 mL. 4.4 Reagents and materials. 4.4.1 Stock Zn solution, 500 μg/mL. Prepare by dissolving 0.500 g of zinc metal in a minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl. 4.4.2 Stock Cd solution, 500 μg/mL. Prepare by dissolving 0.500 g of cadmium metal in minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl.

4.4.3 H2SO4, 98% wt./wt.

4.4.4 H2O2, 30% wt./wt. 4.5 Sampling and test specimens. 4.5.1 Obtain a sample in accordance with TAPPI T 400. 4.5.2 Obtain 1 to 2 g of specimen from various positions on each test unit in the form of small strips. 4.5.3 Dry composite test specimen for 1 h at 105°C and place in a desiccator at least 0.5 h before analyzing. 4.6 Procedure. 4.6.1 Weigh to the third decimal place, a specimen between 1 and 2 g. Add test specimen to a 250 mL

Erlenmeyer flask containing 5 mL of concentrated H2SO4. Attach 3-way parallel side arm connector and 50 mL

cylindrical funnel containing approximately 40 mL of 30% H2O2 to the flask. Support glassware with ring stand and place flask on hot plate. Heat the mixture until the specimen is completely charred and dense white fumes appear. Add

H2O2 at a rate of approximately 1 drop per second until a clear solution results. Evaporate the solution to dryness. Then 9 / Zinc and cadmium in paper T 438 cm-96

cool, add 20 mL HCl (1+1) and 50 mL of water and heat until solution is complete. Allow to cool, then transfer contents of the flask into a 1000 mL volumetric flask and dilute to the mark with water. 4.6.2 Prepare calibration standards by diluting stock zinc and cadmium solutions to 0.1, 0.5, and 1.0 g/mL with 1% (v/v) HCl. Set instrumental conditions according to manufacturer's specifications. Instrument operating conditions are given in 4.6.3. Use either absorbence or concentration readout mode depending on how instrument is equipped. Zero instrument with deionized H2O. Measure calibration standards or set concentration readout. Measure specimens in this sequence: specimen, standard, specimen. Make 3 readings on each specimen. If a specimen concentration readout or absorbence falls outside of the linear range suggested by manufacturer or established by experimentation, dilute solution to get response in linear working range. 4.6.3 Instrument operating conditions.

Analytical Light Flame Element (Slit) wavelength source type

Zinc 0.7 nm 213.9 nm Hollow Air- cathode acetylene lamp (lean) Cadmium 0.7 nm 228.8 nm Hollow Air- cathode acetylene lamp (lean)

4.6.4 Calculation. Calculate the percentages of Zn and/or Cd as follows:

AB Cd, % or Zn, % = (105) C where A = concentration of Zn and Cd, μg/mL. B = dilution factor; example: a 10 mL aliquot of solution is diluted to 100 mL; then dilution factor equals 10. C = weight of test specimen, μg.

T 438 cm-96 Zinc and cadmium in paper / 10

5. Report

5.1 Report the amount of zinc or cadmium as a percentage of the moisture-free material, to the nearest 0.1%, and state the procedure used. 5.2 For the atomic absorption procedure, results are to consist of a listing of the following: 5.2.1 Measured absorbances or concentrations. 5.2.2 A graph on which concentrations of Zn and Cd standards are plotted against their absorbences. 5.2.3 A statement of instrumental conditions to include lamp current, wavelength of measurement, type of flame, type of burner, and any special equipment used for the improvement of instrument performance. 5.2.4 A calculation of % Zn and/or Cd. 5.2.5 Notes on any observances of unusual behavior of either the instrument or the reaction.

6. Precision

6.1 Repeatability: all repeatability values are based on the amount present.

Material Method Repeatability

Zn (0-25%) Polarographic 1% Cd (0-25%) Polarographic 1% Zn (>25%) Volumetric 1% Cd Gravimetric 0.5% Zn (0-5%) Atomic absorption 2% Cd (0-5%) Atomic absorption 2%

6.2 Reproducibility: not known; 6.3 Comparability: not known, in accordance with definition of above terms used as defined in TAPPI T 1200 “Interlaboratory Evaluation of Test Methods to Determine TAPPI Repeatability and Reproducibility.”

7. Additional Information

7.1 Effective date of issue: to be assigned. 7.2 In the atomic absorption method, the extent of interferences from other ions has not been fully examined; however, the absorbances of Zn and Cd are not significantly affected by 10-fold excesses of each other. Ca in a 10-fold 11 / Zinc and cadmium in paper T 438 cm-96

excess depresses Zn absorbance slightly. Ti in a 10-fold excess seems to have no effect on Zn absorbance. Sulfuric acid enhances both absorbances. 7.2.1 Detection limits can be significantly improved by the use of a graphite tube furnace in the atomic absorption procedure. 7.2.2 The atomic absorption procedure can be applied to many other metal ions (5). 7.3 Related method: ASTM D-1224.

References

1. Kolthoff, I. M., and Ligane, J. J., Polarography, 2nd edn., Vol. 2, Interscience, New York, 1952. 2. Muller, O. H., “The Polarographic Method of Analysis,” J. Chem. Educ., Feb.-July, 1981. 3. Strong, C. L., “How to Build a Polarograph,” Scientific American 226 (9): 247 (1962). 4. Atomic Absorption Product Department, Perkin-Elmer Corp., Analytical Methods for Atomic Absorption Spectrophotometry, 1973. 5. Price, J. P., “Utilization of Atomic Absorption Spectroscopy in the Synthetic Fiber Industry,” Tappi 54 (9):1497 (1971).

Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Director of Quality and Standards. g

WI 050114.01

T 438

DRAFT NO. 1

DATE February 15, 2005 TAPPI WORKING GROUP CHAIRMAN to be assigned

SUBJECT CATEGORY Fillers & Pigments Testing

RELATED METHODS See “Additional Information”

CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible for determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health hazards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals.

Zinc and cadmium in paper (Ten-year review of T 438 cm-96)

1. Scope and significance

1.1 This method maybe used for the determination of cadmium and zinc either in paper or in highly opaque pigments. Zinc is usually present in zinc oxide, zinc sulfide, or as lithopone (a combination of zinc sulfide and barium sulfate), which is occasionally used in filled paper, in paper coatings and in high-pressure laminates and wallpaper. Some forms of zinc oxide have photoelectric properties and are found in certain papers used for photo reproduction. Zinc or cadmium pigments are sometimes added to papers to cause fluorescence, and zinc oxide has been used to enhance the cohesive strength of some types of paper coatings. 1.2 Three procedures for each element are described: polarographic, either gravimetric or volumetric, and atomic absorption. The gravimetric procedure is suitable if a polarograph is not available. For the determination of zinc in a zinc-bearing pigment, the volumetric procedure is recommended, because the polarographic procedure is insensitive

Approved by the Standard Specific Interest Group for this Test Method TAPPI T 438 cm-96 Zinc and cadmium in paper / 2

over 25% Zn levels. The polarographic procedure can be used for the determination of zinc and cadmium in paper and for cadmium in cadmium bearing pigments. The preferred procedure for each material is based on its concentration. 1.3 When zinc is to be determined volumetrically (cadmium absent) one precipitation of heavy metals with washing is sufficient. 1.4 In the atomic absorption procedure, sensitivities for 1% absorption are 0.02 mg/mL Zn and 0.03 mg/mL Cd, respectively. The repeatability of this procedure is questionable at present for Zn and Cd concentrations of greater than 5%.

2. Polarographic procedure

2.1 Apparatus. 2.1.1 Polarograph, of the manually operated type. A recording polarograph may be used, although this method is written specifically for a manually operated instrument. 2.1.2 Electrolysis equipment, including a cell, a dropping mercury electrode, an arrangement for maintaining a constant head of mercury above the capillary, and a constant-temperature bath. The cell may be of simple design; for example a test tube is 15 x 85 mm. This cell is fitted with a three-hole notched rubber stopper that will hold the dropping mercury electrode, the contact electrode for the anode (a pool of mercury), and a tube for flushing the solution with nitrogen. 2.1.3 Nitrogen cylinder and tubing. 2.1.4 Other apparatus: pipets, 5, 15, 20, and 50 mL; three 200 mL volumetric flasks. 2.2 Reagents. 2.2.1 Standard zinc solution (1 mL = 0.0010 g of Zn): Dissolve 1.245 g of freshly ignited ZnO in 50 mL of hot HCl (1:10). Cool, dilute with water to 1000 mL in a volumetric flask, and mix.

2.2.2 Standard cadmium solution (1 mL = 0.0010 g of Cd): Dissolve 1.631 g of anhydrous CdCl2 in 100 mL of hot water. Cool, dilute to 100 mL in a volumetric flask and mix. 2.2.3 Gelatin solution (2 g/1000 mL): Dissolve 2.00 g of gelatin in boiling water and dilute the clear solution to 1000 mL. 2.2.4 Nitrogen (with minimum oxygen content).

2.2.5 NH4Cl (crystalline). 2.2.6 HCl (12 N).

2.2.7 NH4OH (14.8 N).

2.2.8 HNO3 (15.7 N). 2.3 Sampling and test specimen. 2.3.1 From each test unit obtained in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Product” (for paper) or TAPPI T 657 “Sampling of Fillers and Pigments” (for pigments), prepare a specimen sufficient to contain at least 10 mg of zinc or 10 mg of cadmium if present. 3 / Zinc and cadmium in paper T 438 cm-96

2.3.2 Normally about 1 g or less of dry paper is sufficient for a single determination; more is needed if its moisture content is unknown. 2.3.3 If the moisture content is unknown, determine it in accordance with TAPPI T 412 “Moisture in Paper and Paperboard.” 2.4 Procedure. 2.4.1 Detailed information regarding the polarographic procedure may be found in the literature (1-3). 2.4.2 Zinc and cadmium factors. 2.4.2.1 Transfer 20.0 and 50 mL aliquots of the standard zinc and cadmium solutions, respectively, to each of two 200 mL volumetric flasks. To each of these flasks, and to a third flask to be carried through the entire procedure as a blank, add 16.6 g of NH4Cl and 5 mL of HCl, and dilute to approximately 150 mL with water. Add 15 mL of NH4OH and 10 mL of gelatin solution. Cool, dilute to the mark with water, and mix. 2.4.2.2 Transfer suitable portions of the resulting solutions to electrolysis cells and remove oxygen by bubbling nitrogen through the solutions for 10 min.

NOTE 1: Since the diffusion current increases with increasing temperature, arrangement must be made to control standards and specimens at a uniform temperature during electrolysis or to make corrections for temperature fluctuations. Other conditions such as drop time and height of the mercury column must also be constant.

2.4.2.3 Determine the increase in the galvanometer deflection in divisions when changing from an applied potential of -0.58 to -0.83 V, and again when changing from -1.09 to -1.40 V for each solution. Adjust the sensitivity of the polarograph circuit so as to obtain optimum increases in galvanometer deflection.

NOTE 2: These voltage settings must be on the residual current plateaus and the diffusion current plateaus, respectively. Since the wave form may be affected by the sensitivity of the galvanometer, a complete polarogram should be plotted and the above settings checked for the particular instrument being used.

2.4.2.4 Multiply the increase in galvanometer deflection obtained by increasing the potential from -0.58 to -0.83 V for each solution by the shunt setting used and plot these values against the amount of cadmium in grams. Next multiply the increase in galvanometer deflection obtained by increasing the potential from -1.09 to -1.40 V for each solution by the shunt settings used and plot these values against the amount of zinc in grams. The three points must fall approximately on a straight line for both metals. T 438 cm-96 Zinc and cadmium in paper / 4

2.4.2.5 Calculate the cadmium and zinc factors as follows:

C1

F1 =

(R1 - B1)

C2

F2 =

(R2 - B2)

where

F1 = cadmium per galvanometer scale division at full sensitivity, gx.

C1 = cadmium in the standard, g.

R1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the standard.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank.

F2 = zinc per galvanometer scale division at full sensitivity, g.

C2 = zinc in the standard, g.

R2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the standard.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank.

NOTE 3: If conditions are kept constant, there is no need to redetermine the cadmium and zinc factors until a new capillary is used.

2.4.3 Analysis of specimen. Transfer about 0.5 g of the dried specimen, weighed to the nearest 0.001 g, to a

400 mL beaker. Add 10 mL of concentrated H2SO4 and heat to char the paper. Oxidize with HNO3 and, when the solution is clear, evaporate to dryness. Add 16.6 g of NH4Cl, 5 mL of HCl, and 50 mL of water. Heat until solution is complete. Cool, transfer to a 200 mL volumetric flask, and dilute to approximately 150 mL with water. Add 15 mL of

NH4OH and 1 mL of gelatin solution. Cool, dilute to 200 mL, and continue in accordance with the procedure for determining the zinc and cadmium factors. 2.4.4 Calculation. Calculate the percentage of cadmium and zinc as follows:

(A1 - B1) F1 Cadmium, % = x 100 W 5 / Zinc and cadmium in paper T 438 cm-96

(A2 - B2) F2 Zinc, % = x 100 W where

A1 = increase galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the specimen.

B1 = increase in galvanometer deflection when the potential is increased from -0.58 to -0.83 V for the blank, in accordance with the procedure.

F1 = cadmium per galvanometer scale division at full sensitivity, g. W = weight of specimen, g.

A2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the specimen.

B2 = increase in galvanometer deflection when the potential is increased from -1.09 to -1.40 V for the blank, in accordance with the procedure.

F2 = zinc per galvanometer scale division at full sensitivity, g.

3. Gravimetric and volumetric procedures

3.1 Apparatus. 3.1.1 For cadmium by the gravimetric procedure. 3.1.1.1 Platinum dish, evaporating about 50 mL. 3.1.1.2 Other apparatus: three 400 mL beakers; 25 and 50 mL graduated cylinders; filter funnel with fine filter paper. 3.1.2 For zinc by the volumetric procedure. As for cadmium and in addition: a 3 and a 5 mL pipet (or small graduated cylinder); medium filter paper; 50 mL buret. 3.2 Reagents. 3.2.1 For cadmium by the gravimetric procedure. 3.2.1.1 Sulfuric acid, concentrated; also dilute (1:1). 3.2.1.2 Nitric acid, concentrated.

3.2.1.3 Hydrogen sulfide, H2S (generator or cylinder). 3.2.1.4 Hydrochloric acid, dilute (3:7). 3.2.2 For zinc by the volumetric procedure. 3.2.2.1 As for cadmium, and in addition:

3.2.2.2 Uranyl acetate indicator. Dissolve 5 g of UO2(CH3COO2) - 2H2O in water, acidify with acetic acid, and dilute to 100 mL.

3.2.2.3 Ammonia, dilute NH4OH (1:1). 3.2.2.4 Hydrochloric acid, concentrated; also dilute (1:1). T 438 cm-96 Zinc and cadmium in paper / 6

3.2.2.5 Sulfuric acid, dilute (5:95). 3.2.2.6 Methyl orange indicator. 3.2.2.7 Zinc, metal, reagent grade. 3.2.2.8 Litmus paper.

3.2.2.9 Potassium ferrocyanide, standard solution 1 mL = 0.01 g of Zn): Dissolve 42.3 g of K4Fe(CN6) -3H2O in water and dilute to 1000 mL. To standardize, transfer 0.3200 - 0.3400 g of zinc to a 400 mL beaker, then dissolve in 10 mL of concentrated HCl and 20 mL of water. Add NH4OH until slightly alkaline to litmus paper; then add HCl until just

acid, plus 3 mL in excess. Dilute to about 250 mL with hot water and heat nearly to boiling. Titrate with K4Fe(CN6) solution, while stirring constantly, until a drop tested on a white porcelain plate with a drop of uranyl acetate indicator shows a brown tinge after standing 1 min. Make a blank determination following the same procedure and using the same

amounts of reagents and water. Calculate the zinc factor of the K4Fe(CN6) solution as follows:

F = Cl(A - B) where

F = zinc equivalent of K4Fe(CN6) solution, g/mL.

A = K4Fe(CN6) solution required to titrate the zinc solution, mL.

B = K4Fe(CN6) solution required to titrate the blank, mL. C = zinc used, g.

NOTE 4: Care should be taken in the handling of K4Fe(CN6) because atmosphere oxygen rapidly converts it to K3Fe(CN6).

3.3 Sampling and test specimen. 3.3.1 Sample as previously described for the polarographic procedure (2.3.1) except use a 4 g specimen for the analysis of zinc in zinc pigments. 3.3.2 Normally about 4 g or less of dry paper is sufficient for a single determination of zinc and cadmium in paper. 3.4 Procedures. 3.4.1 For cadmium by the gravimetric procedure. 3.4.1.1 Place about 4 g of the specimen in a tared weighing bottle, dry to constant weight and weigh to the nearest 5 mg. Transfer to a 400 mL beaker and add 20 mL of concentrated H2SO4. Heat to char the paper and add sufficient HNO3 to oxidize the mixture to a clear solution. Evaporate to dryness and add approximately 100 mL of water and 10 mL of 1:1 H2SO4. Heat to dissolve, and filter if there is any insoluble residue. Dilute to approximately 200 mL, and pass a rapid stream of H2S through the solution for 20 min. Filter through fme paper, but do not wash. Reserve the filtrate. 7 / Zinc and cadmium in paper T 438 cm-96

3.4.1.2 Dissolve the precipitate on the paper with cold 3:7 HCl and wash the paper well with water, catching the solution in the same 400 mL beaker. Add 15 mL of 1:1 H2SO4 and evaporate to dense white fumes. Cool, dilute to 200 mL, and reprecipitate as above. 3.4.1.3 Filter, using a fme paper. Combine the filtrate with that reserved above and reserve the combined filtrates for the determination of zinc. Dissolve the precipitate with cold 3:7 HCl followed by washing with water, receiving the solution in a weighed platinum dish. Add 10 mL of 1:1 H2SO4 and evaporate to dense white fumes.

Remove the excess H2SO4 by heating the dish cautiously, and finally heat to 500 - 600 C. Cool, and weigh as CdSO4. 3.4.1.4 Calculation. Calculate the percentage of cadmium as follows:

A x 0.5392 Cadmium, % = x 100 B where

A = weight of CdSO4, g. B = dry weight of specimen, g.

3.4.2 For zinc by the volumetric procedure. 3.4.2.1 Evaporate the combined filtrates, obtained in accordance with the gravimetric procedure for cadmium, to dryness. Add 5 mL of 1:1 H2SO4 and 100 mL of water, and heat to dissolve. Cool, and add 1:4 NH4OH until just

alkaline. Add 1:4 H2SO4 until neutral to methyl orange, and then add 3 mL of 5:95 H2SO4. Dilute to 200 mL and through a short glass tube, pass a rapid stream of H2S through the solution for 40 min. Leave the tube in the beaker and allow the precipitate to settle for 10 min. 3.4.2.2 Filter, using a medium paper, and wash twice with cold water. Discard filtrate. Place the original beaker and gassing tube under the funnel and punch a hole in the paper. Wash the bulk of the ZnS into the beaker, using hot water. Wash the paper with 40 mL of hot 1:4 HCl and again with hot water. Dissolve the zinc sulfide still adhering to the gassing tube with a minimum quantity of hot 1:4 HCl.

3.4.2.3 Boil to expel H2S. Cool, and add NH4OH until slightly alkaline to litmus paper; then add HCl until just acid, plus 3 mL in excess. Dilute to 250 mL with hot water and heat nearly to boiling. Titrate as described previously. 3.4.2.4 Calculation. Calculate the percentage of zinc in the specimen as follows:

(A - B) F Zn, % = x 100 C where

A = K4Fe(CN6) solution required to titrate the specimen, mL.

B = K4Fe(CN6) solution required to titrate the blanks as described under 3.2.2.9. (standardization of potassium ferrocyanide), mL. T 438 cm-96 Zinc and cadmium in paper / 8

F = zinc equivalent of the K4Fe(CN6) solution, g/mL. C = weight of specimen, g.

4. Atomic absorption procedure

4.1 Summary. A paper specimen is reacted with H2SO4 and H2O2. The resulting solution is diluted, and the concentrations of Zn and/or Cd are measured with a atomic absorption spectrophotometer. A calculation of the weight percents of Zn and/or Cd is then made. 4.2 Definition. Linear working range is that concentration range over which instrument response is propor- tional to concentration. 4.3 Apparatus. 4.3.1 Atomic absorption spectrophotometer. 4.3.2 Erlenmeyer flask, 250 mL with 24/40 ground glass opening. 4.3.3 Parallel side arm connector, 3-way, with 24/40 ground glass joint. 4.3.4 Graduated cylindrical funnel, 50 mL with 24/40 ground glass joint. 4.3.5 Hot plate. 4.3.6 Ring stand. 4.3.7 Analytical balance, capable of reading to 0.001 g. 4.3.8 Volumetric glassware, to include at least one of each of the following flasks, 500 mL, 250 mL, and 100 mL; pipets, 50 mL, 25 mL, 10 mL, and 1 mL. 4.4 Reagents and materials. 4.4.1 Stock Zn solution, 500 g/mL. Prepare by dissolving 0.500 g of zinc metal in a minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl. 4.4.2 Stock Cd solution, 500 g/mL. Prepare by dissolving 0.500 g of cadmium metal in minimum volume of (1:1) HCl and diluting to 1000 mL with 1% (v/v) HCl.

4.4.3 H2SO4, 98% wt./wt.

4.4.4 H2O2, 30% wt./wt. 4.5 Sampling and test specimens. 4.5.1 Obtain a sample in accordance with TAPPI T 400. 4.5.2 Obtain 1 to 2 g of specimen from various positions on each test unit in the form of small strips. 4.5.3 Dry composite test specimen for 1 h at 105 C and place in a desiccator at least 0.5 h before analyzing. 4.6 Procedure. 4.6.1 Weigh to the third decimal place, a specimen between 1 and 2 g. Add test specimen to a 250 mL

Erlenmeyer flask containing 5 mL of concentrated H2SO4. Attach 3-way parallel side arm connector and 50 mL

cylindrical funnel containing approximately 40 mL of 30% H2O2 to the flask. Support glassware with ring stand and place flask on hot plate. Heat the mixture until the specimen is completely charred and dense white fumes appear. Add

H2O2 at a rate of approximately 1 drop per second until a clear solution results. Evaporate the solution to dryness. Then 9 / Zinc and cadmium in paper T 438 cm-96

cool, add 20 mL HCl (1+1) and 50 mL of water and heat until solution is complete. Allow to cool, then transfer contents of the flask into a 1000 mL volumetric flask and dilute to the mark with water. 4.6.2 Prepare calibration standards by diluting stock zinc and cadmium solutions to 0.1, 0.5, and 1.0 g/mL with 1% (v/v) HCl. Set instrumental conditions according to manufacturer's specifications. Instrument operating conditions are given in 4.6.3. Use either absorbence or concentration readout mode depending on how instrument is equipped. Zero instrument with deionized H2O. Measure calibration standards or set concentration readout. Measure specimens in this sequence: specimen, standard, specimen. Make 3 readings on each specimen. If a specimen concentration readout or absorbence falls outside of the linear range suggested by manufacturer or established by experimentation, dilute solution to get response in linear working range. 4.6.3 Instrument operating conditions.

Analytical Light Flame Element (Slit) wavelength source type

Zinc 0.7 nm 213.9 nm Hollow Air- cathode acetylene lamp (lean) Cadmium 0.7 nm 228.8 nm Hollow Air- cathode acetylene lamp (lean)

4.6.4 Calculation. Calculate the percentages of Zn and/or Cd as follows:

AB Cd, % or Zn, % = (105) C where A = concentration of Zn and Cd, g/mL. B = dilution factor; example: a 10 mL aliquot of solution is diluted to 100 mL; then dilution factor equals 10. C = weight of test specimen, g.

T 438 cm-96 Zinc and cadmium in paper / 10

5. Report

5.1 Report the amount of zinc or cadmium as a percentage of the moisture-free material, to the nearest 0.1%, and state the procedure used. 5.2 For the atomic absorption procedure, results are to consist of a listing of the following: 5.2.1 Measured absorbances or concentrations. 5.2.2 A graph on which concentrations of Zn and Cd standards are plotted against their absorbences. 5.2.3 A statement of instrumental conditions to include lamp current, wavelength of measurement, type of flame, type of burner, and any special equipment used for the improvement of instrument performance. 5.2.4 A calculation of % Zn and/or Cd. 5.2.5 Notes on any observances of unusual behavior of either the instrument or the reaction.

6. Precision

6.1 Repeatability: all repeatability values are based on the amount present.

Material Method Repeatability

Zn (0-25%) Polarographic 1% Cd (0-25%) Polarographic 1% Zn (>25%) Volumetric 1% Cd Gravimetric 0.5% Zn (0-5%) Atomic absorption 2% Cd (0-5%) Atomic absorption 2%

6.2 Reproducibility: not known; 6.3 Comparability: not known, in accordance with definition of above terms used as defined in TAPPI T 1206 “Precision Statement for Test Methods.”

7. Additional Information

7.1 Effective date of issue: to be assigned. 7.2 In the atomic absorption method, the extent of interferences from other ions has not been fully examined; however, the absorbances of Zn and Cd are not significantly affected by 10-fold excesses of each other. Ca in a 10-fold 11 / Zinc and cadmium in paper T 438 cm-96

excess depresses Zn absorbance slightly. Ti in a 10-fold excess seems to have no effect on Zn absorbance. Sulfuric acid enhances both absorbances. 7.2.1 Detection limits can be significantly improved by the use of a graphite tube furnace in the atomic absorption procedure. 7.2.2 The atomic absorption procedure can be applied to many other metal ions (5). 7.3 Related method: ASTM D-1224.

References

1. Kolthoff, I. M., and Ligane, J. J., Polarography, 2nd edn., Vol. 2, Interscience, New York, 1952. 2. Muller, O. H., “The Polarographic Method of Analysis,” J. Chem. Educ., Feb.-July, 1981. 3. Strong, C. L., “How to Build a Polarograph,” Scientific American 226 (9): 247 (1962). 4. Atomic Absorption Product Department, Perkin-Elmer Corp., Analytical Methods for Atomic Absorption Spectrophotometry, 1973. 5. Price, J. P., “Utilization of Atomic Absorption Spectroscopy in the Synthetic Fiber Industry,” Tappi 54 (9):1497 (1971).

Your comments and suggestions on this procedure are earnestly requested and should be sent to the TAPPI Director of Quality and Standards. g