ONLINE LOW-LEVEL SCREENING OF POLAR PESTICIDES IN DRINKING AND SURFACE WATERS BY LIQUID-CHROMATOGRAPHY THERMOSPRAY MASS-SPECTROMETRY

Mass spectra of 39 carbamate, triazine, phenylurea and organophosphorus polar pesticides were obtained by liquid chromatography-mass spectrometry with a thermospray interface. The analytes generated [M + H]+ or [M + NH4]+ as the base peak with methanol-0.1 M ammonium acetate as the mobile phase in the discharge positive-ion mode. Chlorophenols showed much better sensitivity in the negative-ion mode; their spectra were dominated by the deprotonated molecular ion. Trace enrichment of these pesticides on a 10 mm x 3.0 mm I.D. precolumn packed with C18-bonded silica was coupled on-line with reversed-phase column liquid chromatography-thermospray mass spectrometry (LC-TSP-MS). The LC separation was carried out on a 250 x 4.6 mm I.D. C18-bonded silica column using a linear methanol-aqueous ammonium acetate gradient [10:90 to 90:10 (v/v) in 45 min]. When optimized TSP-MS conditions and 50-ml water samples were used, the detection limits for the pollutants tested typically were in the 2-90 ng/l range with time-scheduled selected-ion monitoring; the repeatability was good and the LC-TSP-MS system was robust. Several surface and drinking water samples were analysed and low levels of simazine, atrazine, isoproturon and diuron were detected.