A liquid chromatography-tandem mass spectrometry（LC-MS/MS） method for the simultaneous determination of 40 antibacterial agents including tetracycline, metronidazole, ofloxacin and sulfapyridine in cosmetics was established. The samples were extracted with 20% acetonitrile （containing 0.5% formic acid） as the extraction solvent. The LC part used 0.5% formic acid aqueous solution as the mobile phase A and 0.5% formic acid in acetonitrile solution as the mobile phase B, gradient elution, the injection volume was 2 μL, the flow rate was 0.3 mL/min, and the column temperature was 30 ℃. The MS part was determined by electrospray ion source, positive ion multiple reaction monitoring mode （MRM）, and the external standard method was used for quantitative analysis. The results show that the linear range of 40 antibiotics was within 20-100 μg/L, the correlation coefficient was more than 0.997, and the detection limit was within 0.025-0.25 μg/g. The average recovery rate of 40 antibiotics was 73.8%-109.1% at the low, medium and high spiked mass concentrations. Among the 84 batches of samples screened, 1 batch of samples detected metronidazole, 1 batch of samples detected ciprofloxacin, and 1 batch of samples detected metronidazole and ofloxacin. The method has good selectivity, sensitivity and accuracy, and can be used for the simultaneous determination of 40 illegally added antibacterial agents in cosmetics.
