Alpha Analytical, Inc. ID No.: 2221 Facility: Westborough Revision 3 Department: Wet Chemistry Published Date:11/2/2012 7:58:09 AM Title: Total Sulfide, Methylene Blue Method Page 1 of 10 Total Sulfide, Methylene Blue Method References: EPA 376.2: Methods for the Chemical Analysis of Water and Wastes, EPA 600/ 4-82-055, 1982. SM 4500S2-AD: Standard Methods for the Examination of Water and Wastewater, APHA-AWWA-WPCF, 21 st Edition, 2000. EPA 9030B: SW-846, Test Methods for Evaluating Solid Waste: Physical/Chemical Methods, EPA SW-846, Update III, 1997. 1. Scope and Application Matrices: This method is applicable to water, wastewater and seawater samples. Definitions: Refer to Alpha Analytical Quality Manual. Sulfide often is present in groundwater, especially in hot springs. Its common presence in wastewaters comes partly from the decomposition of organic matter, sometimes from industrial wastes, but mostly from the bacterial reduction of sulfate. Hydrogen sulfide escaping into the air from sulfide-containing wastewater causes odor nuisances. The threshold odor concentration of H 2S in clean water is between 0.025 and 0.25µg/L. H 2S is very toxic and has claimed the lives of numerous workers in sewers. It attacks metals directly and has indirectly caused serious corrosion of concrete sewers because it is oxidized biologically to H 2SO 4 on the pipe wall. From an analytical standpoint, three categories of sulfide in water and wastewater are distinguished: ♦ Total sulfide includes dissolved H 2S and HS-, as well as acid-soluble metallic sulfides present in suspended matter. The S -2 is negligible, amounting to less than 0.5% of the dissolved sulfide at pH 12, less than 0.05% at pH 11, etc. Copper and silver sulfides are so insoluble that they do not respond in ordinary sulfide determinations; they can be ignored for practical purposes. ♦ Dissolved sulfide is that remaining after suspended solids have been removed by flocculation and settling. Un-ionized hydrogen sulfide may be calculated from the concentration of dissolved sulfide, the sample pH, and the practical ionization constant of H 2S. The data report packages present the documentation of any method modification related to the samples tested. Depending upon the nature of the modification and the extent of intended use, the laboratory may be required to demonstrate that the modifications will produce equivalent results for the matrix. Approval of all method modifications is by one or more of the following laboratory personnel before performing the modification: Area Supervisor, Department Supervisor, Laboratory Director, or Quality Assurance Officer. This method is restricted to use by or under the supervision of trained analysts. Each analyst must demonstrate the ability to generate acceptable results with this method by performing an initial demonstration of capability, analyzing a proficiency test sample and completing the record of training. After initial demonstration, ongoing demonstration is based on acceptable laboratory performance of at least a quarterly laboratory control sample or acceptable performance from an annual proficiency test sample. A major modification to this procedure requires demonstration of performance. The identification of major method modification requiring performance demonstration is directed by the Quality Assurance Officer and/or Laboratory Director on a case-by-case basis. Printouts of this document may be out of date and should be considered uncontrolled. To accomplish work, the published version of the document should be viewed online. Document Type: SOP-Technical Pre-Qualtrax Document ID: SOP 07-30 Issue 2 Rev 1 Alpha Analytical, Inc. ID No.: 2221 Facility: Westborough Revision 3 Department: Wet Chemistry Published Date:11/2/2012 7:58:09 AM Title: Total Sulfide, Methylene Blue Method Page 2 of 10 2. Summary of Method Sulfide is separated from the sample matrix by suspending the sample in a hydrochloric acid solution and vigorous agitation. Hydrogen sulfide gas is released from the sample and collected in a gas scrubbing bottle cotaining sodium hydroxide. The methylene blue method is based on the reaction of sulfide, mild oxidizing agent potassium dichromate, and dimethyl-p- phenylenediamine to produce methylene blue. 2.1 Method Modifications from Reference None. 3. Reporting Limits The reported detection limit is 0.1 mg/L. 4. Interferences 4.1 Strong reducing agents interfere in the methylene blue test by preventing formation of the blue color. Thiosulfate at concentrations about 10mg/L may retard color formation or completely prevent it. Sulfide itself prevents the reaction if its concentration is very high, in the range of several hundred milligrams per liter. To avoid the possibility of false negative results, use the antimony method to obtain a qualitative result in industrial wastes likely to contain sulfide but showing no color by the methylene blue method. Iodide, which is likely to be present in oil-field wastewaters, may diminish color formation if its concentration exceeds 2mg/L. Ferrocyanide produces a blue color. 4.2 Eliminate interferences due to sulfite, thiosulfate, iodide, and many other soluble substances (but not ferrocyanide), by precipitating ZnS. 4.3 Interference Removal or Sample Concentration: Put 0.15mL (3 drops) zinc acetate solution into a 100mL glass bottle, fill with sample, and add 0.10mL (2 drops) 6N NaOH solution. Stopper, making sure no air bubbles are present and mix by rotating back and forth vigorously about a transverse axis. Add enough NaOH to produce a pH above 9. Let precipitate settle for 30 minutes. The treated sample is relatively stable and can be held for several hours. However, if much iron is present, oxidation may be fairly rapid. 5. Health and Safety The toxicity or carcinogenicity of each reagent and standard used in this method is not fully established; however, each chemical compound should be treated as a potential health hazard. From this viewpoint, exposure to these chemicals must be reduced to the lowest possible level by whatever means available. A reference file of material safety data sheets is available to all personnel involved in the chemical analysis. Additional references to laboratory safety are available in the Chemical Hygiene Plan. All personnel handling environmental samples known to contain or to have been in contact with municipal waste must follow safety practices for handling known disease causative agents. Printouts of this document may be out of date and should be considered uncontrolled. To accomplish work, the published version of the document should be viewed online. Document Type: SOP-Technical Pre-Qualtrax Document ID: SOP 07-30 Issue 2 Rev 1 Alpha Analytical, Inc. ID No.: 2221 Facility: Westborough Revision 3 Department: Wet Chemistry Published Date:11/2/2012 7:58:09 AM Title: Total Sulfide, Methylene Blue Method Page 3 of 10 6. Sample Collection, Preservation, Shipping and Handling 6.1 Sample Collection Take samples with minimum aeration in either a glass or plastic bottle. Fill the bottle completely and cover. Aqueous samples are collected in a 250mL plastic bottle, soil/solid samples are collected in an amber glass container. 6.2 Sample Preservation All samples must be preserved with 2N zinc acetate (Section 8.8) and 6N sodium hydroxide (Section 8.9). Use four drops of 2N zinc acetate solution per 100mL aqueous sample. Adjust the pH to greater than 9.0 with 6N NaOH. 6.3 Sample Shipping No specific requirements. 6.4 Sample Handling Samples are stored refrigerated at 4 ± 2° C. Soil samples are analyzed within a 28-day holding time. Aqueous samples are analyzed within a 7-day holding time. 7. Equipment and Supplies 7.1 Spectrophotometer, Genesys 10vis: For use at a wavelength of 664nm with cells providing light paths of 1cm. 7.2 Test Tubes: 25mL capacity 7.3 Pipets: Glass, volumetric, various volumes 7.4 Volumetric Flasks: 100mL and 1L volumes 7.5 Erlenmeyer Flasks: 125mL volume 7.6 Three-neck Flask: 500mL volume, 24/40 standard taper joints. 7.7 Dropping funnel: 100mL volume, 24/40 joint. 7.8 Purge gas inlet tube: 24/40 joint with coarse frit. 7.9 Purge gas outlet: 24/40 joint reduced to ¼ in. tube. 7.10 Gas scrubbing bottles: 125mL volume, with ¼ inch o.d. inlet and outlet tubes. 7.11 Tubing: ¼ inch o.d. polytetrafluoroethylene (PTFE) or polypropylene. 7.12 Magnetic Stirrer 7.13 Nitrogen gas: 5.0 Ultra pure. Printouts of this document may be out of date and should be considered uncontrolled. To accomplish work, the published version of the document should be viewed online. Document Type: SOP-Technical Pre-Qualtrax Document ID: SOP 07-30 Issue 2 Rev 1 Alpha Analytical, Inc. ID No.: 2221 Facility: Westborough Revision 3 Department: Wet Chemistry Published Date:11/2/2012 7:58:09 AM Title: Total Sulfide, Methylene Blue Method Page 4 of 10 7.14 Nitrogen regulator 7.15 Flowmeter 7.16 Teflon-coated stirring bar 7.17 Analytical Balance: Capable of weighing 0.1g. 7.18 Glass fiber filter disks: 90mm 7.19 Filtration Apparatus: With membrane filter funnel. 7.20 Suction flask 7.21 Vacuum pump 8. Reagents and Standard 8.1 2 different sources. Stock Sulfide Solution, approximately 0.05M: Weigh 12 grams of Na 2S · 9H 2O (Section 8.13) and add to a 1L volumetric flask. Bring to volume with DI water. Mix by swirling gently to prevent oxygen entrapment. Transfer into a 1L amber glass container and store at room temperature. This solution reacts slowly with oxygen but the change is unimportant within a few hours. 8.1.1 Standardization against thiosulfate solution Immediately after preparation, standardize the Stock Sulfide Solution as follows. Also standardize the Stock Solution if the % recovery falls below 75%. 8.1.1.1 Pipet 10mL of 0.025N standard iodine solution (Section 8.5) into each of two 125mL Erlenmeyer flasks.