High-performance liquid chromatographic determination of fenbendazole and its metabolites, sulphoxide and sulphone, in fish muscle tissue

An HPLC method for the determination of fenbendazole (FBZ) and its metabolites, fenbendazole sulphoxide (oxfendazole. FBZ-SO) and fenbendazole sulphone (FBZ-SO2) in trout and eel tissue is described. The compounds are extracted with ethyl acetate and the extract, after addition of hexane, is concentrated and cleaned up on a silica gel solid-phase extraction column. After elution with 3% acetic acid in methanol the reconstituted eluate is analysed on a Lichrosorb RP8 column, the mobile phase being 0.05 M ammonium phosphate (pH=5): acetonitrile:methanol (55:28:17,v/v). Detection is performed at 297 nm. The average recovery in trout muscle tissue over the concentration range 10-500 mu g/kg is 75.7+/-3.3% and 77.5+/-4.1% for FBZ-SO and FBZ-SO2, respectively, and for FBZ the recovery is 76.3+/-5.5% over the range 15-750 mu g/kg.