Determination of Thiabendazole and 5-Hydroxythiabendazole in Livestock Foods by HPLC-UV

Thiabendazole (TBZ) is a benzimidazole antibacterial agent used as an anthelminthic for livestock. 5-Hydroxythiabendazole (5-OH TBZ) is a metabolite formed by hydroxylation of TBZ in an animal's body. The recovery of 5-OH TBZ from animals by extraction in conventional TBZ analysis, which employs a strongly alkaline (pH 11.0) buffer, is as low as 50%. In order to establish a method for simultaneous analysis of TBZ and 5-OH TBZ with high recovery, we examined the optimum pH of a buffer for extraction, a suitable solvent for extraction, and a clean-up column. As a result, it was found that the optimum pH of the buffer was 9.0 and that suitable solvents were ethyl acetate (AcOEt) for pig muscle and liver, and MeCN for pig fat and cow's milk. Among the three types of solid phase extraction (SPE) clean-up columns investigated, the highest recovery for both chemicals was achieved by using an alumina N (ALN) column.