Abstract: An ultra-performance liquid chromatography coupled with high resolution time-of-flight mass spectrometry method (UPLC/HRTOF-MS) has been developed for the simultaneous analysis of 19 antibiotics in dairy products. The sample was treated with acetonitrile and acidic acetonitrile to remove protein and fat, and then the supernatant was concentrated with a concentrator system. The antibiotics in the prepared sample were separated on a BEH column, and then qualitatively and quantitatively analyzed by HRTOF-MS in positive ionization mode within 10 min. A screening database containing the qualitative information of the antibiotics was built with TargetAnalysis software. Matrix matching was used in the antibiotic analysis to compensate for the matrix effects that influence analytical response. The linear range of the antibiotics was 10~500 or 15~1000 μg/L. The limits of detection (LOD) were from 3 to 5 μg/L. At the spiked levels of 20 and 100 μg/L, the average recoveries were from 68.4% to 96.7% with the relative standard deviations ranging from 2.1% to 12.5%. The screening results of a spiked milk sample showed that all the spiked antibiotics could be detected with their deviations of retention time ≤0.1 min, the deviations of mass ＜5 mDa, the degrees of isotope pattern match ≥87.4%, and most spiked antibiotics were detected with high scores. Furthermore, the developed method was applied for the analysis of antibiotics in more than 40 milk and dairy products of seven manufacturers, and the target antibiotics were not detected in all the samples. The method is rapid, sensitive and easy to operate, and is suitable for the screening of antibiotic residues in milk and dairy products.

Key words: antibiotics, dairy products, milk, screening, time-of-flight mass spectrometry (TOF MS), ultra performance liquid chromatography (UPLC)