Fully automated standard addition method for the quantification of 29 polar pesticide metabolites in different water bodies using LC-MS/MS

Abstract

A reliable quantification by LC-ESI-MS/MS as the most suitable analytical method for polar substances in the aquatic environment is usually hampered by matrix effects from co-eluting compounds, which are unavoidably present in environmental samples. The standard addition method (SAM) is the most appropriate method to compensate matrix effects. However, when performed manually, this method is too labour- and time-intensive for routine analysis. In the present work, a fully automated SAM using a multi-purpose sample manager "Open Architecture UPLC®-MS/MS" (ultra-performance liquid chromatography tandem mass spectrometry) was developed for the sensitive and reliable determination of 29 polar pesticide metabolites in environmental samples. A four-point SAM was conducted parallel to direct-injection UPLC-ESI-MS/MS determination that was followed by a work flow to calculate the analyte concentrations including monitoring of required quality criteria. Several parameters regarding the SAM, chromatography and mass spectrometry conditions were optimised in order to obtain a fast as well as reliable analytical method. The matrix effects were examined by comparison of the SAM with an external calibration method. The accuracy of the SAM was investigated by recovery tests in samples of different catchment areas. The method detection limit was estimated to be between 1 and 10 ng/L for all metabolites by direct injection of a 10-μL sample. The relative standard deviation values were between 2 and 10% at the end of calibration range (30 ng/L). About 200 samples from different water bodies were examined with this method in the Rhine and Ruhr region of North Rhine-Westphalia (Germany). Approximately 94% of the analysed samples contained measurable amounts of metabolites. For most metabolites, low concentrations ≤0.10 μg/L were determined. Only for three metabolites were the concentrations in ground water significantly higher (up to 20 μg/L). In none of the examined drinking water samples were the health-related indication values (between 1 and 3 μg/L) for non-relevant metabolites exceeded.