DETERMINATION OF ORGANOPHOSPHORUS PESTICIDES AND THEIR TRANSFORMATIONPRODUCTS IN RIVER WATERS BY AUTOMATED ONLINE SOLID-PHASE EXTRACTION FOLLOWED BY THERMOSPRAY LIQUID-CHROMATOGRAPHY MASS-SPECTROMETRY

The trace-level determination of ten priority organophosphorus (OF) pe sticides (e.g. chlorpyrifos-methyl, diazinon, disulfoton, fenthion, fe namiphos) and various transformation products (TPs; e.g. disulfoton su lfoxide, fenthion sulfoxide etc.) using automated on-line solid-phase extraction (SPE) with C-18 precolumns followed by LC-MS and thermospra y interface with time-scheduled selected-ion monitoring (SIM) was deve loped. Two main ions (usually [M + H](+) and [M + NH4](+) or [M + CH3C N](+)) were used for each pesticide in the positive ion (PI) detection mode, while [M - H](-) and [M + HCOO](-) ions were used in the negati ve ion (NI) mode. The proposed method requires 100 ml of sample for a limit of detection (LOD) of 0.01-0.1 mu g/l. Calibration graphs were c onstructed by preconcentrating 100 ml of water spiked with the pestici de mixture at various concentrations (from 0.025 to 2 mu g/l). Good li nearity was observed for most of the analytes studied. The experimenta l setup described in this paper was applied to study the kinetics of d egradation of ten organophosphorus pesticides in spiked river water sa mples. The different samples were first analyzed by an automated on-li ne precolumn exchange system (OSP-2) followed by LC with diode array d etection. To confirm the identity of the organophosphorus pesticides d etected, the samples were then analyzed by automated on-line SPE-LC-MS . The method permitted unequivocal identification of many of the TPs f armed during the experiments, e.g. the ore-derivatives of chlorpyrifos -methyl, temephos and pyridafenthion, fenamiphos sulfoxide. Many of th ese TPs are here reported for the first time since previously used MS- based techniques were not sensitive enough.