Determination of dimetridazole, metronidazole and ronidazole in salmon and honey by liquid chromatography coupled with tandem mass spectrometry

A liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method was developed to determine the residues of dimetridazole (DMZ), metronidazole (MNZ) and ronidazole (RNZ) in salmon and honey. These compounds were extracted with ethyl acetate from samples and cleaned up using a silica solid phase extraction (SPE) cartridge. These compounds were determined by reversed-phase LC using a C18 column with distilled water-methanol as the mobile phase, and MS detection in the positive mode by applying selected reaction monitoring (SRM). DMZ-d(3), MNZ-(13)C(2),(15)N(2) and RNZ-d(3) were used as internal standards. The method was validated in salmon and honey spiked with these compounds at 0.4-2 µg/kg, and average recoveries were in the range of 91.2-107.0%. Repeatability was 1.7-17.1% and intermediate precision was less than 20%. The detection limits of DMZ, MNZ and RNZ in salmon and honey were 0.05-0.2 µg/kg. The method was applied to 3 salmon and 20 honey samples. The concentrations of these compounds in all samples were lower than the detection limits established by the Ministry of Health, Labour and Welfare in Japan.