One-step extraction for a high throughput multiresidue analysis of chiral and achiral pesticides in milk

Abstract

Pesticides are among the potential contaminants of cow's milk, but the literature is lacking in methods aimed at the analysis of chiral pesticides even if many of them are massively used as racemates. Owing to the different toxicity and biodegradation rate of enantiomers, their analysis is a urgent need in a fundamental staple such as milk, especially because it is a food highly consumed by children. The following work describes a high throughput method for the simultaneous analysis of eleven pesticides, five out of which are racemic mixtures of optical isomers and one is an equimolar mixture of geometric isomers. The extraction procedure allows one to process 18 milk samples per hour thanks to its quickness and ease, albeit the matrix complexity. Two approaches, typically applied for protein precipitation separately (lowering of the medium dielectric constant with cold acetonitrile and salting out effect with ammonium sulphate), were combined to maximize protein removal. The salting out phenomenon also promoted the water/acetonitrile separation and favoured the analyte transfer into the organic phase. After evaporation, the reconstituted extracts were analysed by enantioselective high-performance liquid chromatography combined with dual-polarity tandem mass spectrometry, allowing the complete separation of seventeen chromatographic peaks in a 15-min run. The method was then validated following the Commission Decision 2002/657/EC and its updates. Absolute recoveries, evaluated at three fortification levels, spanned between 69.4 and 88.5 %. The intra-day and inter-day precision was lower than 10.5 % and 17.5 %, respectively. Besides decision limits and detection capabilities, limits of detection (0.011–1.622 μg/kg) and limits of quantitation (0.103–3.770 μg/kg) were also calculated. Calibration curves were built in matrix, in a linear dynamic range between 0.1–60 μg/kg, with determination coefficients higher than 0.9924. The method was finally evaluated with four metrics (AgreePrep, BAGI, SPMS, complexMo-GAPI) and compared with other methods from the literature, showing higher analytical standards, throughput and practicability.