Abstract: A gas chromatography-ion trap tandem mass spectrometry method was developed for the determination of DMZ, RNZ, SNZ, MNZ and ONZ residues in swine muscle. The nitroimidazole residues were extracted with dichloromethane, followed by reextracted with hydrochloric acid. The acid extract was made basified with K2HPO4, followed by extracted with dichloromethane. The final solution was carefully evaporated just to dryness with a vacuum evaporator (water bath at 40 ℃). The remaining residues was dissolved with 3 mL ethyl acetate. The solution was transferred into a derivation tube, evaporated to dryness under a weak nitrogen stream and derivatised with a solution of 50 μL of BSA-50 μL of i-octane for 60 min at 50 ℃ to produce trimethylsilylderivatives (TMSderivatives). The resulting mixture was directly injected into the GC-MS/MS system. It was shown that the calibration curves were linear with a correlation coefficients (r) over 0.998 in range of 0.005-1.6 μg/mL. The limits of detection were 0.2 μg/kg for RNZ, 0.5 μg/kg for SNZ, 1.0 μg/kg for DMZ, MNZ and ONZ. Recoveries of five nitroimidazoles in tissues spiked at 0.2-4.0 μg/kg were 74％-82％, the interday relative standard deviation was less than 13%. These results suggested that the developed method was a sensitive and accurate method for the determination of nitroimidazole residues in swine muscle.

Key words: nitroimidazole, swine, muscle, residues, gas chromatographyion trap tandem mass spectrometry