Abstract: A rapid method was developed and validated for the simultaneous identification and quantitation of the residues of 5-nitroimidazoles and their metabolites in eggs by isotope dilution-ultra-high performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The samples were extracted with acetonitrile, purified with octadecylsilane-bonded silica gel as sorbent, and defatted with n-hexane. The target compounds were separated in the LC system by gradient elution, and detected using an electrospray ionization (ESI) source in the positive ion mode with multiple reaction monitoring (MRM). Under the optimal conditions, the calibration curves for seven nitroimidazoles were linear in the concentration range of 0.5–20 ng/mL, with correlation coefficient exceeding 0.999. The limits of detection (LOD) and quantification (LOQ) were 0.1–0.25 and 0.3–1.0 μg/kg, respectively. The average recoveries at three spiked levels (0.5, 1.0 and 5.0 μg/kg) were 96.5%–112.7%, with relative standard deviations (RSDs) (n = 6) of 0.82%–8.14%. The proposed method was used for the determination of nitroimidazoles in egg samples from Food Analysis Performance Assessment Scheme (FAPAS) with satisfactory results. The RSDs between the results and the assigned values were less than 10%. This method could accurately detect the seven nitroimidazoles and was validated to be suitable for 38 batches of commercial eggs. The developed method is convenient, sensitive and accurate, and 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