Abstract: A rapid confirmatory method has been developed and validated for the simultaneous identification, confirmation and quantitation of 5-nitroimidazoles and their metabolites in eggs by ultra-high performance liquid chromatography tandem mass spectrometry. Egg samples were extracted with acetonitrile. The extracts were purified with octadecyl bonded silica gel adsorbent, and defatted with n-hexane. The compounds were separated in the liquid phase system using gradient elution. The analytes were detected using MS/MS with positive electrospray ionization source under the multiple reaction monitoring modes. Quantitative analysis is performed by internal standard method. Under the optimal conditions, the standard curves of seven nitroimidazoles were linear in the range of 0.5~20 ng/mL, with the correlation coefficient exceeding 0.999.The limits of the detection and limits of the quantification were 0.1~0.25μg/kg and 0.3~1.0μg/kg；The average recoveries at tree levels (0.5, 1.0 and 5.0 μg/kg) were 96.5% ~112.7%, with the relative standard deviations(RSDs) (n=6) were 0.82%～8.14%. The established analytical method was used for the determination of nitroimidazoles in egg sample from Food Analysis Performance Assessment Scheme (FAPAS), and the results were satisfactory. The RSDs between the results and the assigned value was less than 10%, and the spiked recoveries were ideal. It showed that the method can be used for accurate quantification of the seven nitroimidazole drugs in eggs. Additionally, the applicability of the method was verified by testing 38 batches of egg samples. The developed method is convenient, sensitive and accurate, which can be applied for daily monitoring of 5-nitroimidazoles and their metabolites in eggs.

Key words: ultra-high performance liquid chromatography-tandem mass spectrometry, nitroimidazoles, isotope dilution, egg