Determination of fenbendazole and its metabolites in trout by a high-performance liquid chromatographic method†

Abstract

A high-performance liquid chromatographic (HPLC) method based on solid phase extraction was developed for the simultaneous determination of fenbendazole (FBZ), fenbendazole sulfoxide (FBZ-SO) and fenbendazole sulfone (FBZ-SO₂) in trout muscle and skin tissues. The compounds were extracted with acetonitrile and the extract was concentrated and cleaned up by solid phase extraction on C₁₈ and CN cartridges. The extract was analysed by reversed-phase gradient HPLC on a C₁₈ column followed by ultraviolet detection at 290 nm. The method’s detection limits were 4.0 µg kg^–1 for FBZ, 4.5 µg kg^–1 for FBZ-SO and 3.8 µg kg^–1 for FBZ-SO₂. The mean recovery in muscle was 88% for FBZ, 94% for FBZ-SO and 92% for FBZ-SO₂ at a level of 5–150 µg kg^–1. The corresponding mean recoveries in skin tissue were 88, 81 and 86% at a level of 10–100 µg kg^–1. The mean relative repeatability standard deviation was 9.2% at a level of 5 µg kg^–1, 5.9% at a level of 10–100 µg kg^–1 and 2.3% at a level of 150 µg kg^–1. The method was applied to trout given feed containing FBZ in an aquaculture pilot plant. The three compounds FBZ, FBZ-SO and FBZ-SO₂ were all detected in muscle and skin tissues shortly after administration. The concentrations were generally highest in skin tissue.