Quantitative multiresidue analysis of antibiotics in milk and milk powder by ultra-performance liquid chromatography coupled to tandem quadrupole mass spectrometry

⿢A new and single SPE step of removing lipids from milk or milk powder was developed.⿢Cleaner LC⿿MS chromatograms were achieved with this single SPE step in comparison with no SPE-treated milk.⿢The method has been successfully used to detect 61 antibiotics in milk or milk powder. A simple and fast multiresidue extraction and purification method was developed for the determination of 61 veterinary drugs, belonging to seven classes, in milk and milk powder. The extraction depends on the acetonitrile solvent, followed by a single step to remove lipids with fatty acid chains using a new reversed phase SPE without traditional pre-equilibration and washing steps before eluting SPE. The purifying lipid effect of the present preparation method was evaluated by comparing the response changes of ion peak areas of the milk endogenous metabolites before and after SPE treatment using ultra-fast LC coupled to tandem quadrupole and TOF MS. Subsequently, UPLC coupled to tandem quadrupole MS was performed for the quantitative analysis of milk and milk powder samples spiked with 61 veterinary drugs, including β-lactam, macrolide, amide alcohol, forest amine, sulfanilamide, tetracyclines, and quinolones antibiotics. This method is very simple, fast, sensitive, and selective, and allows the good recoveries of all compounds, with a recovery range of 61.5⿿118.6%, and coefficients of variation of less than 11.6%. The 61 compounds behave in the dynamic range 0.01⿿200μgkg⿿1, with correlation coefficient >0.99. The limits of quantification for the analytes are in the range 0.01⿿5.18μgkg⿿1. Finally, this method has been successfully applied to the screening of veterinary drugs in 50 commercial bovine milk and milk powder samples, and ceftiofur and ciprofloxacin were detected in some brand samples.