Ultra performance liquid chromatography-tandem mass spectrometry for the determination of 5-nitroimidazoles and their metabolites in egg

An ultra performance liquid chromatography (UPLC) coupled to tandem mass spectrometry (MS/MS) procedure was developed for the determination of five 5-nitroimidazoles (dimetridazole, ipronidazole, metronidazole, ronidazole and ternidazole) and three of their metabolites (1-methyl-2-hydroxymethyl-5-nitroimidazole, 1-(2-hydroxyethyl)-2-hydroxymethyl-5-nitroimidazole and 1-methyl-2-(2′-hydroxyisopropyl)-5-nitroimidazole) in egg matrices. Conditions for UPLC separation and electrospray ionization MS/MS in the positive ion mode were optimized. Samples were prepared by liquid-liquid extraction with buffered aqueous 2.5% trichloroacetic acid followed by solid-phase extraction on a Strata-X-C cartridge with reversed-phase and cation-exchange functionalities. The method’s performance was evaluated in accordance with Commission Decision 2002/657/EC, applying the alternative matrix-comprehensive in-house validation approach using specially designed InterVal software. The method was robust against different sample matrix and SPE cartridges, operator change, and changes in sample extract storage. Acceptable apparent recoveries (76 to 109%) were obtained for all analytes. The decision limits (CC_α) and detection capabilities (CC_α) were within the ranges of 0.19–2.62 and 0.26–4.29 μg kg⁻¹. For all compounds the calibration curve linearity was good with correlation coefficients greater than 0.99. Fifteen eggs and ten whole egg powder samples obtained commercially in Lithuania were analyzed by UPLC-MS/MS; none were found contaminated by 5-nitroimidazoles or their metabolites.