Analytical Method for Nitroimidazoles and Their Major Metabolites in Livestock and Fishery Products Using LC-MS/MS

A sensitive and reliable method for the simultaneous determination of four nitroimidazoles (ipronidazole (IPZ), dimetridazole (DMZ), metronidazole (MNZ) and ronidazole (RNZ)) and three metabolites (IPZ-OH, MNZ-OH and 2-hydroxymethyl-1-methyl-5-nitroimidazole (HMMNI)) in livestock and fishery products was developed. The analytes were extracted from samples with acetone containing acetic acid. The crude extracts were defatted by liquid–liquid partition using acetonitrile and n-hexane followed by solid-phase extraction using a cartridge column packed with divinylbenzene–N-vinylpyrolidone copolymer bearing sulfo groups. The analytes in the eluate from the cartridge column were extracted with ethyl acetate after addition of ammonium sulfate. The solvent was removed from the extract, and the residue was dissolved in 0.1 vol% formic acid. The HPLC separation was performed on a C18 column with a gradient formed from water containing 0.1 vol% formic acid and acetonitrile containing 0.1 vol% formic acid. For detection of the analytes, tandem mass spectrometry with positive ion electrospray ionization was used. The recovery tests were performed on 10 livestock and fishery products. The truenesse ranged from 74.6 to 111.1%, with repeatability of 0.5–8.3 RSD% for the entire procedure. The limit of quantification was 0.0001 mg/kg for IPZ, IPZ-OH, MNZ and MNZ-OH, and 0.0002 mg/mg for DMZ, RNZ and HMMNI.