| Abstract
| - Livers of goats orally dosed with [phenyl(U)-14C]benomyl contained radioactive residues which werenot extractable using conventional, solvent-based extraction methods. We report a new residuemethod capable of enhanced extraction of benomyl-derived residues with selective and sensitivequantitation capability for methyl 4-hydroxybenzimidazol-2-ylcarbamate (4-HBC), methyl 5-hydroxybenzimidazol-2-ylcarbamate (5-HBC), and methyl benzimidazol-2-ylcarbamate (MBC). Thismethod involves rigorous Raney-nickel reduction of hypothesized thioether bonds between benomylresidues and polar cellular components. Following acidic dehydration (desulfurization), the polarbenomyl-derived residues are extracted into ethyl acetate and analyzed by LC/MS/MS. We haveshown this method to be superior to alternative extraction approaches. When applied to goat livertissue containing [phenyl(U)-14C]benomyl-bound residues, the extraction efficiency of total radioactiveresidues was approximately 30%, and the major benomyl-derived residue was 5-HBC (91−95% ofextractable residue) with minor levels of carbendazim (MBC) (5−9%). HPLC/LSC data wereconsistent with the LC/MS/MS data. The overall method satisfies U.S. regulatory requirements inextraction efficiency, selectivity in detection, and limits of quantitation for benomyl-bound residues. Keywords: Benomyl; benzimidazole; carbendazim; desulfurization; fungicide; mass spectrometry;metabolite; pesticide; Raney-nickel
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