DETERMINATION OF POLAR PESTICIDES BY PHASE-TRANSFER-CATALYZED DERIVATIZATION AND NEGATIVE-ION CHEMICAL-IONIZATION GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

A single-step procedure for the extraction and derivatization of carboxylic pesticides from aqueous samples is described. The acidic compounds, including phenoxy herbicides, were extracted from aqueous samples using tetrahexylammonium hydrogensulphate as a catalyst and were subsequently derivatized with pentafluorobenzyl bromide to volatile stable and electron-capturing derivatives. Analysis was performed by gas chromatography with electron-capture detection combined with negative-ion chemical ionization mass spectrometry. The recovery of the compounds was 108 +/- 8%. Detection limits were typically 0.05 mug/l, using mass unit resolution. Highly contaminated samples required increased resolution (1000 less-than-or-equal-to R(f) less-than-or-equal-to 4000) for reduced chemical background and enhanced selectivity for detection at low-ppb levels. The method was applied to the determination of some phenoxycarboxylic pesticides in surface water and in blood samples.