On-line low-level screening of polar pesticides in drinking and surface waters by liquid chromatography—thermospray mass spectrometry

Abstract

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 + NH 4] + 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 × 3.0 mm I.D. precolumn packed with C 18-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 × 4.6 mm I.D. C 18-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.