Abstract: A method for determination of five kinds of nitroimidazole compound (metronidazole (MNZ),ronidazole (RNZ),dimetridazole (DMZ),hydroxyl metronidazole (MNZOH) and 2-hydroxymethyl-1-methyl-5-nitroimidazole (HMMNI)) in whelk dispelling cosmetics by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was established.The target analyte was extracted from the product sample with ethyl acetate as solvent,and the extract was separated on a Hypersil GOLD C₁₈ column (2.1 mm×100 mm,3 μm),sequentially eluted with acetone,methanol and blend solution with V(ammonia water)∶V(acetonitrile)=5∶95,detected using LC-MS/MS in the multiple reaction monitoring (MRM) positive ion mode,and quantified by external standard matrix method.The results indicated that good linearity displays when mass concentration of MNZ,RNZ and DMZ is within 0~50 μg/L,and when mass concentration of MNZOH and HMMNI is within 0~100 μg/L.Linear correlation coefficient (R²) is higher than 0.99.In the spiked test of three levels,the average recovery rate is in the range of 84.3%-115.0%,and relative standard deviation (RSD) is in the range of 1.66%-10.30% (n=6).This analysis method meets the testing requirements for detection and confirmation.

Key words: whelk dispelling cosmetics, nitroimidazole compound, liquid chromatography-tandem mass spectrometry