Rapid quantitative screening assay of trace benzimidazole residues in milk by liquid chromatography

A simple, rapid, and sensitive liquid chromatographic (LC) assay for quantitative screening of albendazole 2-aminosulfone, albendazole sulfoxide, oxibendazole, oxfendazole, albendazole sulfone, p-hydroxyfenbendazole, albendazole, mebendazole, fenbendazole sulfone, and fenbendazole residues in milk was developed. Samples are made basic (pH 10) and extracted with ethyl acetate. Extracts are partitioned with water, evaporated to dryness, reconstituted with mobile phase, and analyzed isocratically by ion-pair reversed-phase LC at 292 nm. Overall recoveries ranged from 79 to 100%. Linearity was excellent in the fortification range examined (5.3-200 ng/mL). Precision data, based on within- and between-days variations, suggested an overall relative standard deviation of 2.0 to 5.8%. The method was successfully used to quantitate albendazole and fenbendazole and metabolites in milk from 2 drug-treated dairy cows.