Development of a multiresidue method for analyzing pesticide traces in water based on solid- phase extraction and electrospray liquid chromatography mass spectrometry

The GC/MS technique is still the staple for analyzing pesticide residues in water. However, many of the currentuse pesticides are not amenable to GC/MS analysis. As shown recently in some published reports, the LC/MS technique could fill this gap. We developed a sensitive and specific LC/MS method for determining 45 widely used pesticides having a broad range of polarity in water. This method involves passing 4, 2, and 1 L, respectively, of drinking water, groundwater, and river water through a 0.5-g graphitized carbon black (Carbograph 4) cartridge at ca. 100 mL/min. In all cases, recoveries of the analytes were better than 80%, except for carbendazim (76%). The performance of the electrospray/mass spectrometer (ES/ MS) detector was optimized by adopting in-glass distilled methanol as the organic modifier and 10ímol/L trifluoroacetic acid as an additive to the mobile phase. The effects of varying the electrical field in the ES/MS transport region on both sensitivity and specificity of the detector were evaluated. The in-source collision-induced decomposition process afforded great specificity of the method, at little or no expense of sensitivity. For drinking water, the limits of detection (LODs) were calculated from both total ion current chromatograms and extracted ion current profiles. In the former case, LODs ranged between 1 (atrazine) and 9 (butoxycarboxim) ng/L. In the latter case, LODs ranged between 0.06 (malathion) and 1.5 (aldicarb sulfone) ng/L.