Development and Validation of a Multiclass Method for Analysis of Veterinary Drug Residues in Milk Using Ultrahigh Performance Liquid Chromatography Electrospray Ionization Quadrupole Orbitrap Mass Spectrometry.

This paper presents the development and validation of a multiclass method for the analysis of veterinary drug residues in milk using ultrahigh performance liquid chromatography electrospray ionization quadrupole Orbitrap mass spectrometry (UHPLC/ESI Q-Orbitrap). The 12 classes of veterinary drugs (a total of 125) included in this study were endectocides, fluoroquinolones, ionophores, macrolides, nitroimidazole, NSAIDs, β-lactams, penicillins, phenicols, sulfonamides, tetracyclines, and aminoglycosides. Veterinary drug residues in milk were extracted using a modified salting-out supported liquid extraction (SOSLE) method, which entailed the precipitation of milk proteins using an extraction buffer (oxalic acid and EDTA, pH 3) and acetonitrile, a salting-out acetonitrile/water phase separation using ammonium sulfate, and solid-phase extraction (SPE) using polymeric reversed-phase sorbent cartridges. The final extracts were concentrated and reconstituted into a buffer solution and analyzed using UHPLC/ESI Q-Orbitrap mass spectrometry. The developed method was validated using a nested experimental design to evaluate the method performance characteristics, such as overall recovery, intermediate precision, and measurement uncertainty. The method was able to quantify or screen up to 105 veterinary drugs from 11 different classes, except aminoglycosides. The limits of quantification were as low as 1.0 μg/kg, with an analytical range from 1.0 to 100.0 μg/kg in milk.