Rapid and simultaneous determination of amoxicillin, penicillin G, and their major metabolites in bovine milk by ultra-high-performance liquid chromatography-tandem mass spectrometry.

A rapid, sensitive, and specific method for the determination of amoxicillin (AMO), amoxicilloic acid (AMA), amoxicillin diketopiperazine-2',5'-dione (DIKETO), penicillin G (PEN G), benzylpenicilloic acid (BPA-1), benzylpenilloic acid (BPA-2), and benzylpenillic acid (BPA-3) in bovine milk using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) was developed and validated. The method used penicillin V (PEN V) as the internal standard and ethanol for the deproteinisation of bovine milk. Chromatographic separation of the components was performed on a Waters Acquity UPLC® HSS T3 column (100 mm x 2.1 mm, 1.8 μm) using a mixture of 0.15% formic acid in water with 5mM ammonium acetate and acetonitrile as the mobile phase. Gradient elution was performed at a flow rate of 0.25 mL min⁻¹. The mass spectrometer was operated in the positive electrospray ionisation MS/MS mode. The method was fully validated according to EU requirements, including linearity, precision, trueness, limit of quantification, limit of detection, and specificity. The results were within the ranges specified. The established method was successfully applied in the determination of AMO, PEN G, and their major metabolites in 40 commercial bovine milk samples. The results showed that 8 samples were contaminated with BPA-1 or BPA-2. The mean levels (occurrence) of BPA-1 and BPA-2 in positive samples were 287 (50%) and 320 (100%) ng mL⁻¹, respectively. No sample was found to be contaminated with AMO, AMA, DIKETO, PEN G, and BPA-3. These findings could play an important role in food safety, because BPA-1 and BPA-2 metabolites pose possible health risks, although they are not included in the maximum residue limit legislation.