Single laboratory validation of multi-residue extraction and cleanup method for analysis of 50 pesticides, 14 veterinary drugs, and 7 Polychlorinated biphenyls in bovine milk by tandem mass spectrometry.

A QuEChERS-dispersive SPE method was optimized for the simultaneous extraction and cleanup of multi-class pesticide, veterinary drug, and polychlorinated biphenyl (PCB) residues from bovine milk. Milk samples were spiked at concentrations ranging from 0.1 to 10 times the respective EU maximum residue limits (MRLs) or validation limits with 50 pesticides, 14 veterinary drugs, and 7 indicator polychlorinated biphenyls (PCBs). Both LC-MS/MS- and GC-MS/MS-amenable compounds were simultaneously extracted, followed by a cleanup step prior to injection into the LC and GC systems, separately. In the optimized method, linear regression correlation coefficients (R2) ≥0.99 and limits of quantification (LOQ) ≤ EU MRL were achieved for all 71 analytes. Recoveries obtained at 0.5 MRL, 1.0 MRL, and 1.5 MRL ranged from 74% to 109% for the LC pesticide compounds, 65% to 108% for the organochlorine pesticides (OCs), 94% to 112% for the veterinary drugs, and 42% to 91% for the PCB congeners analyzed. Within-laboratory repeatability and reproducibility (RSD%) values were ≤ 20% for 95% of analytes across all 3 spiked levels. Matrix effect values for most analytes indicated satisfactory cleanup and a stable analytical workflow. This simple single extraction and cleanup procedure is suitable for quantitative identification of LC and GC amenable pesticides and veterinary drugs of interest, together with qualitative screening of PCBs in milk, increasing the laboratory throughput and economic viability of multi-residue analysis.