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Effective Date: 6/23/2009 Revision Date: 6/19/2009 Revision Author: Betina Topolski, MI Thompson HG-020-5.13 Page 1 of 6 DIGESTION OF SEDIMENT AND WASTE SAMPLES FOR TOTAL MERCURY ANALYSIS 1. SCOPE AND APPLICATION This SOP describes the digestion of sediment samples for total mercury content. It is a modified version of SW-846 Method 7471 and EPA Method 245.5 and is applicable to the analysis of soils, sediments, sludge and waste samples. The procedure outlined in this SOP is applicable to sediment or waste samples logged in for tests S-HG-H or WASTE-HG-H. 2 SUMMARY OF THE METHOD 2.1. In sediments, both organic and inorganic forms of mercury can exist. In order to analyze for total mercury content, the organic mercury must be oxidized to mercuric ions (Hg+2). 2.2. To accomplish this, each sediment sample is heated in hydrogen peroxide and nitric acid to dissolve the sediment matrix. The sample is then heated and allowed to react with potassium permanganate and potassium persulfate to completely oxidize the mercury in the sample to the Hg+2 state. Total mercury is analyzed for as Hg+2. 3. APPARATUS AND EQUIPMENT 3.1. Nalgene straight-sided, wide-mouthed, 125 mL high-density polyethylene (HDPE) bottles with polypropylene closures. 3.2. Fisher Scientific Isotemp Waterbath 3.3. Pipets 3.3.1. 10-100 uL adjustable Eppendorf pipet 3.3.2. 100-1000 uL adjustable Eppendorf pipet 3.3.3. 1-5 mL adjustable Oxford Macro pipet 3.3.4. 5-10 mL adjustable Oxford Macro pipet 4. REAGENTS AND CHEMICALS 4.1. Trace Metal Grade (TMG) Nitric Acid: If not in laboratory acid storage area, check the chemistry section's acid storage room. 4.2. 30% Hydrogen Peroxide: Store in refrigerator. 4.3. 6% Potassium Permanganate Solution: Add 30 grams of potassium permanganate crystals to a 500 mL Nalgene bottle half full of deionized water and dilute to volume with deionized water. Mix well. Effective Date: 6/23/2009 Revision Date: 6/19/2009 Revision Author: Betina Topolski, MI Thompson HG-020-5.13 Page 2 of 6 4.4. 6% Potassium Persulfate Solution: Add 15 grams of potassium persulfate crystals to a 250 mL Nalgene bottle half full of deionized water and dilute to volume with deionized water. Mix well. Prepare this solution each time digestion is performed. Do NOT store for later use. 4.5. Standards and Spiking Solutions 4.5.1. Commercial Stock Standard 1000 ppm: Commercially available inorganic mercury stock from SPEX, EM Science or other certified vendor. 4.5.2. Working Standard Solution, THG-2 (500 ug/L): This solution is prepared by the Hg analysis group; see SOP HG-012-2. 4.5.3. Working Standard Solution, THG-4 (200 ug/L): This solution is prepared by the Hg analysis group; see SOP HG-012-2. 4.5.4. NIST3133-2 (50 g/L) Standard Reference Material (prepared by mercury analyst). 4.5.5. Buffalo River Sediment NIST2704 (1.47 mg/Kg): Commercially available dry sediment standard from the National Institute of Science and Technology. Store in a desiccator in laboratory. Other suitable Hg sediment standards such as San Joaquin Soil NIST2709 (1.40 mg/Kg) may be used in place of NIST2704. NOTE: Record all reagent and spiking solution names, volume used, the preparer’s initials, serial number and expiration date on the prep sheet and in the reagent prep log. 5. SAMPLE COLLECTION, PRESERVATION, AND HANDLING 5.1. All equipment and glassware should be scrupulously clean to avoid contamination; refer to SOP HG-021-2. 5.2. All sediment samples are stored in the refrigerator in the receiving room of the DEP laboratory. 5.3 Metallic Mercury, some inorganic mercury compounds, and many organic mercury compounds are volatile and unstable. The holding time for solid matrices scheduled for mercury analysis is 28 days. NOTE: The preparation technician should monitor the preparation expiration date on the backlog. It is possible that the sample due date is after the preparation expiration date of the sample. Sorting the backlog by expiration date should help prevent unnecessary preparation expirations. 6. SAMPLE PREPARATION PROCEDURE 6.1. Turn on water bath in sample digestion room and set temperature to 95 C on the control panel. Fill water bath with deionized water up to the fill mark on the bath. Replace the water in the water bath weekly. Effective Date: 6/23/2009 Revision Date: 6/19/2009 Revision Author: Betina Topolski, MI Thompson HG-020-5.13 Page 3 of 6 6.2. Prepare sample digestion bottles by discarding the 10% Aqua Regia cleaning solution that has been stored in them. The dilute Aqua Regia should be discarded in the sink and flushed with ample quantities of tap water. The polyethylene bottles are then rinsed 6-8 times with tap water. Rinse the cap as well with tap water and then replace on the bottle. 6.3. Remove the bottle of 30% Hydrogen Peroxide (H2O2) from the refrigerator and allow it to warm up to room temperature. 6.4. Percent Dry Solids Determination: See SOP MT-055-1, Determination of “Percent Dry Solids.” The % dry solids result is required for each sample so that the final sample result may be reported on a dry weight basis (mg Hg/kg dry material). Note that if using the Hg-S Excel spreadsheet these calculations will be performed automatically as the weights are entered into the proper fields. 6.5. Before weighing out the sample into the digestion bottle, ensure all water has been shaken out of the bottle. Wipe the outside of the bottle with a Kim-wipe if there is moisture on the outside. Place the bottle on the top loading balance and tare the balance so that it reads 0.000 grams. Using a clean stainless steel spatula, carefully transfer approximately 1g of well-mixed sediment into the BOTTOM a pre-labeled digestion bottle. Record the weight EXACTLY on the sediment preparation log-sheet. NOTE: Make sure that NO sample has spilled onto the balance outside of the bottle! Repeat for each sediment sample to be analyzed. When weighing replicate portions of sample for the duplicates and spikes, take time to make sure that the sample weights are close together! 6.6. Choose one sample that is NOT a trip blank, field blank or an equipment blank. Prepare a matrix spike at 0.05 ug by adding 250 uL of 200 ug/L (THG-4) mercury spike to approximately 1 gram of sample into a pre labeled digestion bottle. Record the sample weight EXACTLY. Prepare duplicate matrix spikes for every batch of 20 samples or less analyzed. NOTE: For waste samples, double the amount of spike solution added (Spike Factor = 2.). 6.7 Prepare one LFB by spiking 42 mL of deionized water into a bottle with the same spike solution used for the matrix spikes (250 uL of THG-4). Add ~1.0 g of pre- cleaned perforated glass boiling beads to the bottle. Once again, for waste samples, the amount of spike solution is doubled (Spike Factor = 2). 6.8. Prepare a duplicate sample by weighing out approximately 1 gram of the SAME sample used for the matrix spike into a pre labeled bottle. Label these bottles with an A and B after the sample number to denote the two duplicate samples. Prepare one duplicate sample for every batch of twenty samples or less. 6.9 Prepare a reference standard by weighing out approximately 0.12 grams of NIST2704 (Buffalo river sediment) into a pre labeled bottle. Record the weight the EXACTLY. Prepare one NIST2704 reference for every batch of 20 samples or less analyzed. Another suitable reference standard such as San Joaquin Soil (NIST2709) may be used in place of NIST2704. Effective Date: 6/23/2009 Revision Date: 6/19/2009 Revision Author: Betina Topolski, MI Thompson HG-020-5.13 Page 4 of 6 6.10 Prepare a water reference standard, S-NIST3133 by measuring 38 mL of deionized water into a pre-labeled bottle. Add 4 mL of the 50 ppb NIST3133-2 SRM to the bottle. The total volume will be 42 mL, with a final concentration of 5 ppb. 6.11. Prepare a digestion blank by measuring out 42 mL of deionized water into a pre labeled digestion bottle. Add ~1.0 g of pre-cleaned perforated glass boiling beads to the bottle. Prepare 1 digestion blank for every batch of twenty samples or less. Pre-cleaned perforated glass beads will be used as the solid mercury-free matrix for the preparation of the digestion blank, PQL and lab-fortified blanks (LFBs). 6.12. Prepare a 0.625 ug/L PQL by adding 125 uL of 200 ug/L standard into a pre- labeled digestion bottle filled with 42 mL of deionized water. Add ~ 1.0 g of pre- cleaned perforated glass boiling beads to the bottle. Prepare 1 PQL for every batch of 20 samples or less. 6.13. Add 5.0 mL of Trace Metal grade nitric acid to all sample bottles. Be careful of violent reactions with the sediment matrices. If foaming occurs, gently tap the bottom of the bottle to break foam bubbles. Place the digestion blank and PQL bottles in an ice water bath for 10-15 minutes. 6.14. Add 2.0 mL of 30% hydrogen peroxide solution to all sample bottles except the digestion blank, LFBs, S-NIST3133 and PQL. Hydrogen peroxide is added only to samples consisting of real sediment or waste matrices. Allow the samples to react for at least 15 minutes. 6.15. For each bottle, tighten the cap and gently swirls the vessel. Quickly loosen the cap to vent the built up gases. Repeat for all samples. 6.16. Loosen all caps and place in a 95 C water bath for 5 minutes. Carefully watch bottles for violent reactions or foaming. Remove those bottles from water bath and tap to break foam bubbles. Return to water bath and continue to watch. 6.17. Remove sample rack and allow to cool. Add 40 mL of deionized water to sediments and NIST2704 ONLY. DO NOT add 40 mL of water to standards, digestion blank, LFBs, S-NIST3133 or PQL samples. 6.18. CAREFULLY add 10.0 mL of 6% potassium permanganate solution to all bottles. For all samples, except the digestion blank, LFB, and PQL, if the permanganate purple color does not persist for at least 15 minutes, add sufficient excess 6% KMnO4 to the tube in 1 mL increments until color persists for at least 15 minutes. DO NOT ADD ANY EXTRA PERMANGANATE TO THE DIGESTION BLANK OR THE PQL EVEN IF THE PURPLE COLOR OF THE PERMANGANATE DISAPPEARS. There is excess oxidizer present in them. RECORD HOW MUCH EXTRA PERMANGANATE SOLUTION HAS BEEN ADDED TO THE OTHER SAMPLES. 6.19. Add 4.0 mL of 6% potassium persulfate to all bottles. Tighten Nalgene caps and gently invert the bottles several times to mix. Loosen all caps and return samples Effective Date: 6/23/2009 Revision Date: 6/19/2009 Revision Author: Betina Topolski, MI Thompson HG-020-5.13 Page 5 of 6 to 95 C water bath for one hour. 6.20. Cool samples and tighten caps. Samples can be stored for several days but should preferably be analyzed within 3 days. NOTE: Record the concentrations, solution preparation dates, preparer’s initials, volumes, serial number and expiration date of all standards and spikes that you use in the comments section of the logbook. Make a copy of the logbook pages and place it with the digested sample tubes. This will aid the analyst in performing sample analyses and troubleshooting instrument problems. 7. SAMPLE ANALYSIS PROCEDURE 7.1 Refer to SOP HG-008, “Analysis of Total Mercury in Sediments and Wastes by Cold Vapor Atomic Absorption (CVAA) Spectroscopy” for details on the analysis of the digested samples. 8. QUALITY CONTROL 8.1. Digestion Blank: One per batch of twenty samples or less. 8.2. Sample Matrix Spikes: Two duplicates per batch of twenty samples or less. 8.3. Sample Duplicates: One set of duplicate samples per batch of twenty samples or less. 8.4. S-NIST3133 and NIST2704 or NIST2709 reference standards: One per batch of twenty samples or less. 8.5. Practical Quantitation Level (PQL): One per batch of twenty samples or less. 8.6. Laboratory Fortified Blank (LFB): One or two per spike type per batch of 20 samples or less. NOTE: Using these numbers, you can estimate how many sample bottles that you will need. The water bath holds 40 sample bottles. 9. SAFETY/HAZARDOUS WASTE MANAGEMENT 9.1. Treat all samples as a possible hazard. Wear appropriate laboratory clothing: gloves, safety glasses, lab coat, etc. 9.2. The water bath should be placed in a hood. 9.3. All samples should be vented in a hood. 9.4. Watch for possible violent reactions when adding reagents to the digestion vessels. The addition of reagents should be done in a hood. 9.5. All high level mercury standards (>200 g/L) should be handled with care and Effective Date: 6/23/2009 Revision Date: 6/19/2009 Revision Author: Betina Topolski, MI Thompson HG-020-5.13 Page 6 of 6 treated as hazardous. Unused or expired standards should be disposed as hazardous waste. 10. REFERENCES 10.1. Mercury Group Standards Preparation Procedures, SOP HG-012-2 10.2 Procedure for High Level Mercury Glassware Cleaning, SOP HG-021-2. 10.3. Determination of Percent Dry Solids, SOP MT-055-1. 10.4. Analysis of Total Mercury in Sediments and Wastes by Cold Vapor Atomic Absorption (CVAA) Spectroscopy, SOP HG-008 10.5 SW-846 Method 7471. Appendix of Changes 06/19/2008 A new section (Section 7) for the sample analysis procedure was added. Other minor revisions to the text were made for format and clarity. 06/22/2009 Added section 5.3; edited format of entire SOP; edited nomenclature for consistency.