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 solid-phase 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 mug/l and precisions having a relative standard deviation (R.S.D.) below 4.9% (chlortoluron) was achieved. Instrumental limits of detection of 0.10 mug/l were found with the exception of chlortoluron, diuron and methomyl, for which 0.25 and 0.50 mug/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 mug/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 mug/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 carbarnates, 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. (C) 2003 Elsevier B.V. All rights reserved.