APPLICATION OF ONLINE SOLID-PHASE EXTRACTION FOLLOWED BY LIQUID CHROMATOGRAPHY-THERMOSPRAY MASS-SPECTROMETRY TO THE DETERMINATION OF PESTICIDES IN ENVIRONMENTAL WATERS

A multi-residue method for the trace-level determination of 34 pesticides and various transformation products was developed by using on-line solid-phase extraction and either ten 4.6-mm Empore extraction discs containing C-18 or a conventional precolumn, packed with PRP-1 copolymer, followed by liquid chromatography-thermospray mass spectrometry with time-scheduled selected-ion monitoring. Two main ions (usually [M + H](+) and [M + NH4](+) or [M + CH3CN](+)) were used for each pesticide in the positive-ion operational mode, while [M-H](-) and [M + HCOO](-) ions were used in the negative-ion mode. Losses of CH3NCO were also monitored for many of the carbamate pesticides. The proposed method requires 100 ml of sample for a limit of detection of 0.01-0.4 mu g/l, depending on the particular compound and the operational mode. Calibration graphs were constructed by preconcentrating 100 ml of an estuarine water sample, spiked with the pesticide mixture at various concentration levels, varying from 0.025 to 1.2 mu g/l. Good linearity was observed for sixteen of the analytes studied, the relative standard deviation (n = 5) being 4-13%. Some examples of the trace-level determination of various pesticides in European river and ground water samples are given.