Abstract: A method for simultaneous determination of six kinds of nitroimidazole drug (metronidazole (MNZ),tinidazole (TNZ),ornidazole (ONZ),dimetridazole (DMZ),ronidazole (RNZ) and secnidazole (SCZ)) in acne dispelling cosmetics adopting solid phase extraction (SPE) purification technology and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) was studied and established.Samples were extracted with acidified acetonitrile solution and the extract was purified with cation resin solid phase exchanging column.Then the purified extract was separated with a C₁₈ column,by gradient elution with acetonitrile and water (containing 0.1% formic acid,volume fraction),and detected by tandem mass spectrometry under multiple reaction monitoring (MRM) mode.The results indicated that good linearity displays when mass concentration of the six kinds of nitroimidazole is within 1.0~50.0 μg·L^-1,and all the linear correlation coefficients are higher than 0.999.All the limits of quantification (LOQ) are 0.5 mg·kg^-1.The recoveries of six kinds of nitroimidazole when three levels of standard were spiked into samples of acne dispelling cosmetics (both cream type and lotion type) range from 89.7% to 108.0% with RSD (n=6) from 2.3% to 6.5%.

Key words: acne dispelling cosmetics, nitroimidazoles, high performance liquid chromatography-tandem mass spectrometry, solid phase extraction