Correspondence Comment on “Identification of Halogenated Compounds in Chlorinated Seawater and Drinking Water Produced Offshore Using n-Pentane Extraction and Open-Loop Stripping Technique” SIR: In the recent paper by Kristiansen et al. (1), both n-pentane extraction and open-loop stripping were used to analyze the halogenated compounds in chlorinated waters. In this study, Kristiansen et al. observed the formation of brominated artifacts such as 3-bromo-2methyl-2-butanol (BMB), which was reported as a new ozonation byproduct in water high in bromide (2). Kristiansen et al. concluded that BMB might be an artifact resulting from the reaction of excessive halogen with traces of olefins in the extraction solvent. The effects of different quenching agents on the formation and stability of BMB were also examined. Sodium thiosulfate was suggested as the best choice since it effectively quenches residual chlorine and prevents the formation of BMB but with little effect on the stability of BMB. These findings are in general agreement with some of our own recent work (3, 4). However, the authors should also point out that the use of the extraction salt, sodium chloride, can lead to the formation of new artifacts in unquenced extracts. The ACS grade sodium chloride may contain as much as 0.01% bromide [Indeed, many laboratory chemical suppliers report “approximately 0.01%” for bromide in their chemical assay for ACS grade sodium chloride.] (5). In Kristiansen et al.’s study, 17 g of sodium chloride was added to 50 mL of water sample. Therefore, as much as 34 mg/L bromide was added to these water samples. Since most of the water samples were unquenched, hypobromous acid might be formed and react with organic precursors to yield the aqueous-phase brominated byproducts or react with traces of olefins in the solvent to form brominated artifacts. The use of sodium chloride might not have a significant impact on the analytical results on the chlorinated seawater samples, but it would be expected to significantly affect the results of tap water low in bromide. The comparison between n-pentane extraction and the open-loop stripping might also be affected by sodium chloride addition. The observed superiority of pentane extraction on recovery of
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brominated byproducts might be due to their accelerated formation after the addition of sodium chloride, which contains bromide. In EPA Method 551 (6), sodium chloride is used as an extraction salt. We have observed a number of problems such as high levels of bromoform in water with low levels of bromide when using sodium chloride to analyze unquenched or incompletely quenched samples. This may also explain why Jordan et al. found 33% higher bromoform values by EPA 551 (with NaCl) as compared to EPA 501.2 (without NaCl) (7). We suggest that sodium sulfate should be used as an extraction salt. This compound is less likely to be contaminated with bromide. Therefore, the use of sodium sulfate would make the method more robust to errors in quenching.
Literature Cited (1) Kristiansen, N. K.; Frøshaug, M.; Aune, K. T.; Becher, G. Environ. Sci. Technol. 1994, 28, 1669-1673. (2) Cavanagh, J. E.; Weinberg, H. S.; Gold, A.; Sangalah, R.; Marbury, D.; Glaze, W. H.; Collette, T. W.; Richardson, S. D.; Thurston, A. D. Environ. Sci. Technol. 1992, 26, 1658-1662. (3) Xie, Y.; Reckhow, D. A. In Proceeding of the AWWA Water Quality Technology Conference; AWWA: Denver, CO, 1993; pp 14991511. (4) Xie, Y.; Reckhow, D. A. Environ. Sci. Technol. 1994, 28, 13571360. (5) American Chemical Society Specifications. Reagent Chemicals, 7th ed.; American Chemical Society: Washington, DC, 1986. (6) U.S. EPA Method 551. Determination of Chlorination Disinfection Byproducts and Chlorinated Solvents in Drinking Water by Liquid-Liquid Extraction and Gas Chromatography with Electron-Capture Detection; Environmental Monitoring System Laboratory: Cincinnati, OH, 1990. (7) Jordan, M. D.; Taylor, J. S.; Mulfor, L. A.; Lyn, T. L. In Proceeding of the AWWA Water Quality Technology Conference; AWWA: Denver, CO, 1991; pp 421-437.
Yuefeng Xie* Environmental Programs Penn State Harrisburg Middletown, Pennsylvania 17057
David A. Reckhow Department of Civil & Environmental Engineering University of Massachusetts Amherst, Massachusetts 01003 ES940776Y
0013-936X/96/0930-0720$12.00/0
1996 American Chemical Society
