Arsenic speciation of aqueous environmental samples by derivatization with thioglycolic acid methylester and capillary gas liquid chromatography mass spectrometry

Procedures are described for the determination of dimethylarsinic acid, monomethylarsonic acid, arsenate, and arsenite in aqueous samples. The arsenicals are reacted with thioglycolic acid methyl ester to form volatile trivalent derivatives. The reaction products are extracted into benzene and separated by capillary gas-liquid chromatography. A low-resolution electron-ionization quadrupole mass spectrometer operated in the selective ion-monitoring mode is used to detect the derivatives after chromatographic separation. Method detection limits range from 0.1 ng/mL (ppb) for the alkylarsenic acids to 3 ppb for arsenate and arsenite. The method is shown to be simple, rapid, and quantitative for the determination of selected arsenic species in aqueous environmental samples and drinking water.