Abstract: A method for the analysis of common antibiotics and metronidazole in cosmetics was developed by ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). One gram of each cosmetic sample was extracted by methanol-water containing 0.1 mol/L formic acid (1∶1, v/v). The extracted sample was filtered before being analyzed with UPLC/MS/MS. The effects of formic acid concentration in the mobile phase on the sensitivity and retention time were studied, and the results showed that 1% was the optimum concentration. Seven analytes, minocycline, oxytetracycline, tetracycline, chlortetracycline, doxycycline, chloramphenicol, metronidazole, can be separated and detected in 5 min, which is much faster than that by the conventional liquid chromatography. The detection limits were 3-20 ng/g, and the recoveries were 87%-101%. The calibration curves showed good linearity in the range of 2-1000 μg/L with correlation coefficients larger than 0.995. The method was also applied to determine common antibiotics and metronidazole in 11 real samples from themarket. Chloramphenicol was detected in 2 samples and the concentrations were 0.37% and 0.19%; metronidazole was detected in 1 sample and the concentration was 1.02%; others were not detected.

Key words: antibiotics, cosmetics , metronidazole, ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS)