Multiresidue screening of neutral pesticides in water samples by high performance liquid chromatography–electrospray mass spectrometry

A multiresidue method to screen ultra traces of neutral pesticides from water samples in compliance with European Union regulations is presented, using solidphase extraction (SPE) followed by high performance liquid chromatography coupled to atmospheric pressure electrospray ionisation (ESI) mass spectrometry, SPE/LC–MS(ESI). Calibration conditions of LC–MS(ESI) in the SIM mode, showed excellent linear response for the 12 pesticides studied (carbaryl, carbofuran, methomyl, oxamyl, pirimicarb, chlortoluron, diuron, isoproturon, linuron, atrazine, propazine and simazine) in the range from 1 to 50 (mu)g/l and precisions having a relative standard deviation (R.S.D.) below 4.9% (chlortoluron) was achieved. Instrumental limits of detection of 0.10 (mu)g/l were found with the exception of chlortoluron, diuron and methomyl, for which 0.25 and 0.50 (mu)g/l were measured. The SPE assays using octadecilsilica cartridges are relatively simple and highly reproducible, requiring low volume of water sample (50 ml). For laboratory-spiked water samples having 0.10 (mu)g/l of individual pesticides, good average recoveries were obtained, within 65.0 and 97.8% with a relative standard deviation lower than 12.6% (methomyl). For real matrices, laboratory-spiked drinking and surface water samples at the 0.05 (mu)g/l level, reasonable average recoveries were also achieved, ranging from 75.3 to 96.8% and 67.7 to 105.2%, respectively. The present work establishes a suitable protocol as a guideline for research and routine laboratories, to screen simultaneously carbamates, phenylureas and triazines from water samples. The methodology evidences very good reproducibility and is shown to be a suitable alternative to replace the currently dedicated analytical systems. The limits of detection reached (0.5–3.0 ng/l) clearly cover the maximum concentration admissible for pesticides in water samples, established by the European Union directive.