Multi-residue screening of 100 multi-class veterinary drugs in milk powder by liquid chromatography coupled to quadrupole time-of-flight mass spectrometry

In this study, a simple and rapid multi-residue screening method for the quantification and confirmation of 100 multi-class veterinary drugs in milk powder by the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) method combined with liquid chromatography coupled to quadrupole time-of-flight mass spectrometry was developed. The veterinary drugs investigated belonged to several families such as macrolides, sulfonamides, quinolones, tetracyclines, nitroimidazoles, benzimidazoles, β-agonists, hormones, and tranquilizers. The samples were extracted using a modified QuEChERS procedure: (i) dissolved in a solution of Na2EDTA–McIlvaine buffer (0.1 M, pH 4), (ii) extracted with 5% acetic acid in acetonitrile, and (iii) purified using a C18 sorbent. The linearity, sensitivity, accuracy, repeatability, and reproducibility of the method were fully validated. The average recoveries for the majority of analytes (92.9%) ranged from 70 to 120% at four concentration levels, while the repeatability and reproducibility ranged from 1.1 to 20.1%. A coefficient of correlation (γ2) of 0.995 or above was obtained for all the compounds. The range of the limit of quantification for these compounds in the milk powder was from 0.1 to 25 μg kg−1. More than 93.0% of the analytes were detected when present at 10 μg kg−1 or less in the milk powder samples. For the screening method, the data of the precursor and product ions of the target analytes were simultaneously acquired under the All Ions MS/MS mode in a single run. A homemade library including the elemental composition, retention time, and full-scan product ions was utilized for the confirmation and identification of the target compounds. The applicability of the screening method was verified by applying to real milk powder samples, and certain veterinary drugs were detected in some cases.