Ion-pairing liquid chromatographic determination of benzimidazole fungicides in foods

A method is described for determining residues in foods of thiabendazole, thiophanate methyl, the di-oxygen analogue metabolite [dimethyl 4,4'-O-phenylene bis (allophanate)] that is the metabolite name of the latter, and methyl-2-benzimidazole carbamate, which is the major metabolite and fungitoxic principle common to both thiophanate methyl and benomyl. The residues are extracted from the product using methanol and are partitioned into dichloromethane after initial acidification and again after subsequent alkalinization of the extract. Residues are separated and quantified by reverse-phase liquid chromatography using an ion-pairing mobile phase with UV and fluorescence detectors in tandem. Recoveries from 7 different food crops fortified at 0.2-35 ppm levels ranged from 64 to 105%.