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Spontaneous methylation of haloacetic acids in methanolic stock solutions

TitleSpontaneous methylation of haloacetic acids in methanolic stock solutions
Publication TypeJournal Article
Year of Publication1993
AuthorsXie Y, Reckhow DA, Rajan R.V.
JournalEnvironmental Science & Technology
Start Page1232
Date Published06/1993

Since dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were first identified in chlorinated drinking water (11, a number of studies have shown these compounds to be ubiquitous and of human health concern (2-5). Accordingly, the US. Environmental Protection Agency (USEPA) is considering these two major haloacetic acids (HAAs) for regulation in the disinfectants and disinfection byproducts (D-DBP) rule (6). The presence of monochloroacetic acid (MCAA), monobromoacetic acids (MBAA), dibromoacetic acid (DBAA), and mixed bromo/chloroacetic acids has also been reported in recent years (3, 7). The USEPA is considering the regulation of some of these compounds in the coming D-DBP rule as well (6). Two analytical methods for HAAs, USEPA method 552 and a microextraction method, are currently being used to analyze MCAA, DCAA, TCAA, MBAA, DBAA, and bromochloroacetic acid in treated drinking waters (8-10). Due to its low volatility and high aqueous solubility, methanol is the solvent of choice for the preparation of standard stock solutins of haloacetic acids prescribed by the microextraction method (9). This method recommended that primary stock solutions, kept at -10 "C, can be used for 6 months and secondary stock solutions may be kept for 2 months. In EPA method 552 (a), methyl tert-butyl ether (MtBE) is used to prepare primary and secondary stock solutions. However, this method also allows the use of methanol as an alternative to MtBE for the preparation of secondary stock solutions (10). In the present study, spontaneous methylation of haloacetic acids was tested in five seta of methanolic stocks stored at -10 "C. The rates of methylation of DCAA at 60 and 70 "C were determined and then extrapolated to ambient and subambient temperatures. The significance of spontaneous methylation of HAA methanolic stocks on water quality monitoring and process research is also discussed.