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Literature Cited (1) Kimbrough, D. E.; Wakakuwa, J. R. Environ. Sci. Technol. 1989, 23, 898-900. (2) Abu-Samra, A,; Morris, J. S.; Koirtyohann, S. R. Anal. Chem. 1975, 47,1475-1477.
(3) Barret, P.; Davidowski, L. J., Jr.; Penaro, K. W.; Copeland, T. R. Anal. Chem. 1978,50, 1021-1023. (4) Kingston, H. M., Jassie, L. B., Eds. Introduction to Microwave Sample Preparation: Theory and Practice; American Chemical Society: Washington, DC, 1988. (5) Matthes, S. A,; Farrell, R. F.; Mackie, A. J. Journal of Technical Progress Report, U S . Bureau of Mines, 1983; No. 120.
(6) Nadkarni, R. A. Anal. Chem. 1984, 56, 2233-2237. (7) Hewitt, A. D.; Reynolds, C. M. CRREL SR 90-19, Cold Regions Research and Engineering Laboratory, 72 Lyme Rd., Hanover, NH 03755, 1990. (8) Bajo, S.; Suter, U. Anal. Chem. 1982, 54, 49-51. (9) Gallorini, M.; Greenberg, R. R.; Gills, T. B. Anal. Chem. 1978,50, 1479-1481. (10) Merry, R. H.; Zarcinas, B. A. Analyst 1980,105, 558-563. (11) Berry, F. J.; Brett, M. E. Inorg. Chim. Acta 1984, 83, 167-169. (12) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry, 5th ed.; Whiley-Interscience: New York, 1988; p 401. (13) Matthes, S. A. U.S. Department of the Interior, Bureau of Mines, Albany, OR, personal communication. (14) Tatro, M. E. Spectroscopy (Eugene,Oreg.) 1990,5, 17-20. (15) Matthes, S. A. Bureau of Mines Report of Investigations 8484, 1980. Alan
D. Hewitt," James H. Cragin
Cold Regions Research and Engineering Laboratory Hanover, New Hampshire 03755-1290
SIR: T h e letter from Hewitt and Cragin points up the on-going dilemma of laboratories using EPA methods, which applies both to C L P laboratories and others t h a t rely on the RCRA methods manual SW-846. Their review of the chemistry of antimony in acid digestions is consistent with the work done in our laboratory. However, we would like to add a few comments t h a t may be important. Antimony will be "lost" in a digestion procedure whether or not silicates are present, if it is not already in
Environ. Sci. Technol., Vol. 25, No. 5, 1991
As Hewitt and Cragin point out, the more HC1 that is present in the digestion mixture, the better the recoveries. However, mixtures of HCl and nitric acid produce an interesting phenomenon: a small amount of antimony is always trapped in the filter paper. The amount varies with the sample matrix, the total amount of antimony present, and the molecular form of the antimony, but it is rarely more than lo00 pg (2). At high concentrations this amount can be insignificant and ignored, but for samples where there is less than 5000 pg total antimony, this amount can be critical. For example, EPA SW 846 method 3050, which ends up being about 1:l HC1 to nitric acid, can accurately quantify a 2.0-g sample of soil contaminated with 10 000 pg/g antimony, but not one a t 100 pg/g. T h e same phenomenon can be seen with draft method 6020 and the aqua regia digestion used a t our laboratory. To eliminate this phenomenon, the filter paper is washed with hot (95 "C) HC1 and then hot (95 "C) deionized water in our aqua regia method. For concentrations of greater than 20 000 pg/g, the filter paper and residue are redigested in 5 mL of concentrated HC1. These steps may be useful in microwave digestion procedures. Literature Cited
Funding for this work was provided by the Program Manager, Rocky Mountain Arsenal, through the U S . Army Toxic and Hazardous Materials Agency (USATHAMA) under contract DA-2522-IAR-1689, Durant Graves, Project Monitor. We especially thank Steve A. Matthes of the Bureau of Mines (Albany, O R ) , who provided helpful advice and suggestions throughout this study. We also thank Dr. Clarence Grant and Dr. Thomas Jenkins o f USACRREL, who reviewed the manuscript.
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a soluble form. For example, an aqueous solution of potassium antimony tartrate can be added to nitric acid a t low concentrations and be recovered. However, if dry potassium antimony tartrate is digested with nitric acid, it will not be quantitatively solubilized, even in the absence of silicates ( I ) .
(1) Kimbrough, D. E.; Wakakuwa J. A study of the Linear Ranges of Several Acid Digestion Procedures. In Proceeding of the EPA's Sixth Annual Symposium on Solid Waste
Testing and Quality Assurance;Washington DC, July 1990. (2) Kimbrough, D. E.; Wakakuwa, J. An Inter-Laboratory Study Comparing EPA SW 846 Method 3050 with a Pro-
posed Alternative from the California Department of Health Services. In Proceeding of The EPA's Fifth Annual Symposium on Solid Waste Testing and Quality Assurance; Washington DC, July 1989. Reprinted in Waste Testing and Quality Assurance: Third Volume ASTM STP 1075, Tatsch, C. E., Ed.; American Society for Testing and Ma-
terials, Philadelphia, PA, 1991. Janice R. Wakakuwa," David E. Kimbrough Department of Health Services Division of Laboratories Southern California Laboratory 1449 West Temple Street Los Angeles, California 90026-5698
0013-936X/9 1/0925-0986$02.50/0
0 1991 American Chemical Society
