Confirmation and quantitation of selected sulfonylurea, imidazolinone, and sulfonamide herbicides in surface water using electrospray LC/MS

A multianalyte method has been developed for the confirmation and quantitation of 16 selected sulfonylurea, imidazolinone, and sulfonamide herbicides in surface water. Samples are acidified, the analytes are extracted using RP-102 extraction cartridges, and the extracts are cleaned-up using an anion-exchange cartridge (SAX) stacked on top of an alumina cartridge. The final extracts are evaporated to dryness, redissolved in 10:90 or 20:80 acetonitrile/water, and analyzed using electrospray LC/MS. Confirmation criteria were defined so that identification of the analytes could be made with a reasonable degree of scientific certainty. Confirmation required that (1) LC/MS retention times of the analytes be within 1% of the retention times of the standards, (2) the molecular ion and two characteristic fragment ions per analyte be present, and (3) ion abundance ratios of the fragment ions relative to the molecular ion be within 20% of the ion ratios obtained for the standards. Each of the analytes in all of the samples used to validate this method met these confirmation criteria. Quantitation of the analytes at 0.1 and 1.0 ppb was demonstrated, with average recoveries between 70% and 114% and relative standard deviations that were less than 13%. The limit of quantitation (LOQ) for this method is 0.1 ppb (ng/mL) for all analytes. Six water types were used for the validation of this method.