Multi-residue analysis of pesticides in surface water by liquid chromatography quadrupole-Orbitrap high resolution tandem mass spectrometry.

A quantitative targeted screening method for the determination of residues of a broad group of more than 250 pesticides in surface water samples was developed and validated. Substances were isolated from the sample matrix by solid-phase extraction (SPE), using hydrophilic-lipophilic balanced polymeric sorbents (HLB), and analysed by reversed-phase liquid chromatography (LC) - Orbitrap high-resolution mass spectrometry (HRMS). Compounds were quantified in full scan acquisition mode, while accurate data dependant MS2 analysis was simultaneously triggered for the unambiguous identification of the targeted substances. This analytical protocol combines simplicity and robustness, with quantitative recoveries for 215 of the pesticides, negligible matrix effects during electrospray ionisation (ESI) and limits of quantification (LOQs) below 5 ng L-1 for 204 of the analysed compounds. Method capabilities were checked at qualitative and quantitative levels, analysing a set of four river water samples from rural areas in the Southwest of England. A total of 33 different pesticides were found in these samples with MCPA present at the highest concentration, in excess of 130 ng L-1. Retrospective examination of the LC-HRMS chromatograms permitted the identification of an additional pesticide and a group of nine antimicrobials and veterinary drugs that were also present in the processed samples.