Determination of Haloacetic Acids, Bromate, and Dalapon in Drinking Water by Ion Chromatography Electrospray Ionization Tandem Mass Spectrometry.

 Summary:

Residual chlorine present in drinking water samples is reacted with ammonium chloride to form chloramines, effectively preventing chlorine-mediated formation of method analytes during storage. In addition, the combined chlorine residual prevents microbial degradation in the sample. Prior to analysis, isotopically enriched analytes (monochloroacetic acid-2-13C, monobromoacetic acid-1-13C, dichloroacetic acid-2-13C, and trichloroacetic acid-2-13C) are added to the samples as internal standards. An aliquot of the sample is injected without cleanup or concentration onto an ion exchange column specifically designed to separate method analytes from the following common anions (matrix components) in drinking water: chloride, carbonate, sulfate, and nitrate. The matrix components in the column eluate are monitored via conductivity detection and then diverted to waste; the analytes of interest are directed into the ESI-MS/MS system. Acetonitrile is added post-column to enhance desolvation of the method analytes in the ESI interface. Each method analyte is qualitatively identified via a unique mass transition, and the concentration is calculated using the integrated peak area and the internal standard technique.

Scope and Application:

Method 557 is a direct-inject, ion chromatography, negative-ion electrospray ionization, tandem mass spectrometry (IC-ESI-MS/MS) method for the determination of haloacetic acids in finished drinking water. Bromate and dalapon (2,2-dichloropropionic acid) may be measured concurrently with the haloacetic acids. Real time, chromatographic separation of common anions in drinking water (matrix elimination) is a key feature of this method.