Determination of the marker residue of albendazole in milk using ion-pair liquid chromatography and fluorescence detection

A simple, rapid, and sensitive ion-pair liquid chromatographic (LC) method for the determination of the sulphoxide, sulphone and 2-aminosulphone metabolites that comprise the marker residue of albendazole in milk has been developed. Samples are made alkaline with sodium hydroxide solution and extracted with ethyl acetate, and the extracts are cleaned-up by partition with water. Chromatographic separation of the analytes is performed isocratically in presence of both positive and negative pairing ions, while detection is carried out fluorometrically using excitation and emission wavelengths of 290 and 320 nm, respectively. The method shows accuracy and precision figures well within acceptable limits. Overall recoveries were 85.3+/-9.0%, 96.4+/-6.2% and 83.4+/-7.5% for the sulphoxide, sulphone and 2-aminosulphone metabolites, respectively while precision data, based on within- and between-days variation, suggested overall relative standard deviation values ranging from 2.9% to 6.0%. The good analytical characteristics of the method could allow limits of detection in the low ng ml(-1) range to be realised. The method was successfully applied to determine total residues in milk of a dairy cow treated with albendazole and, also, to study the stability of the residues with storage.