AUTOMATED SAMPLE PREPARATION WITH EXTRACTION COLUMNS FOLLOWED BY LIQUID-CHROMATOGRAPHY IONSPRAY MASS-SPECTROMETRY - INTERFERENCES, DETERMINATION AND DEGRADATION OF POLAR ORGANOPHOSPHORUS PESTICIDES IN WATER SAMPLES

The determination of polar and/or thermally labile organophosphorus pe sticides trichlorfon, dichlorvos, dimethoate, oxydemeton-methyl, mevin phos (cis and trans), demeton-S-methyl, fenamiphos, fenitrothion, fent hion and diazinon in water samples was investigated using solid-phase extraction followed by liquid chromatography-ionspray mass spectrometr y (LC-ISP-MS). Pesticides were spiked at 0.2 mu g/l in ground water sa mples and 200 ml were preconcentrated by using an ASPEC XL system. To improve the recovery of the most volatile pesticides such as dichlorvo s, a further drying step with a Baker Spe 12 G apparatus with the vacu um set at 15 p.s.i. was included. A further evaporation step was appli ed with a gentle stream of nitrogen. A variety of materials (Amberchro m, LiChrolut EN, cyclohexyl, SDB, C-18 and Isolute ENV) were used for the isolation of the target pesticides. The elution step took place at 1 ml/min, with a 5-min contact time between the eluent and the sorben t. LC-ISP-MS permitted the identification of diethyl and di-n-butyl ph thalates present as impurities in the cartridge materials. The presenc e of transformation products of the pesticides, e.g., fenthion sulfoxi de, was also observed. The influence of pH and the water matrix (disti lled and ground water) on the extraction efficiency was examined. The use of LC-ISP-MS permitted cis- and trans-mevinphos to be distinguishe d in the water sample owing to the presence of a specific ion at m/z 9 9. The limits of detection of the overall method were in the range 0.0 1-0.20 mu g/l using LC-ISP-MS with selected-ion monitoring.