| A liquid chromatography-tandem mass spectrometric(LC-ESI MS/MS) method was developed for the simultaneous determination of nitromidazoles and their metabolites residues,including metronidazole(MNZ),ronidazole(RNZ),dimetridazole(DMZ),metronidazole-OH(MNZOH) and 2-hydroxymethyl-1-methyl-5-nitroimidazole(HMMNI) or dimetridazole-OH(DMZOH) in aquatic products.Samples were homogeneously extracted with methanol-acetone(3∶1) in 0.5 mol/L sodium dihydrogen phosphate(NaH2PO4) solution(pH 8.0).The supernatant solution was concentrated by rotary evaporation followed by liquid-liquid partition with ethyl acetate.The fat was removed by acetonitrile-hexane distribution.The analytes were separated on a C18 column(Agilent ZORBAX SB C18 RRHD，100 mm×2.1 mm，1.8 μm) by gradient elution using a mobile phase of 0.1% formic acid solution and acetonitrile containing 0.1% formic acid,and detected by LC-ESI MS/MS under multiple reaction monitoring mode(MRM) via positive electrospray ionization(ESI+).Isotope dilution internal standard method was used for quantitation analysis．The results showed that the calibration curves of five kinds of compounds were linear in a certain concentration range(0.25-50 μg/L) with correlation coefficients of 0.998 6-0.999 7.The limits of quantitation(LOQs,S/N≥10) were 0.1 μg/kg.The average recoveries at three spiked levels of 0.1,0.5,10.0 μg/kg were between 70.7% and 105.1% with relative standard deviations(RSDs) of 1.7%-8.1%.The method showed advantages of rapidness,efficiency and high repeatability，and could meet the requirements for determination of nitromidazole residues in aquatic products． |