Comparative methodology in the determination of α-oxocarboxylates in aqueous solution: Ion chromatography versus gas chromatography after oximation, extraction and esterification

The α-oxocarboxylates (α-ketocarboxylates) and the corresponding α-oxoacids (α-ketoacids) have been reported as byproducts of ozonation of potable water supplies. Some of these species also occur in biophysiological systems. Five analytes were investigated in this study: oxoethanoate (glyoxylate), 2-oxopropanoate (pyruvate), 2-oxobutanoate (2-ketobutyrate), 2-oxopentanoate (2-ketovalerate) and oxopropanedioate (ketomalonate, mesoxalate). Ion chromatography (IC) and gas chromatography (GC) were evaluated for the quantitation of these analytes at concentrations ≤200 ng ml−1. For the IC method, the samples are run directly with minimal to no pre-treatment. For the GC method, the analytes must be derivatized with O-(2,3,4,5,6-pentafluorobenzyl)oxylamine to form oximes. The oximes are extracted into tert.-butyl methyl ether and the carboxylic acid is esterified (methylated) with diazomethane. It was concluded that the ion chromatographic determination is significantly superior to the gas chromatographic method for these analytes.