Development of liquid chromatographic methods for determination of quinocetone and its main metabolites in edible tissues of swine and chicken

Quinocetone (QCT), a new antimicrobial growth promotant of quinoxalines, can effectively improve the growth and feed efficiency of food animals with more safety than is provided by olaquindox and carbadox. To clarify its metabolism and residue levels in animals, a liquid chromatographic method with UV-Vis detection was developed for the determination of QCT and its main metabolites, desoxyquinocetone (DQCT) and 3-methylquinoxaline-2-carboxylic acid (MQCA), in muscle, liver, kidney, and fat of swine and chicken. For sample pretreatment, QCT and DQCT were extracted with ethyl acetate and purified with iso-octane; after alkaline hydrolysis of the tissue, MQCA was extracted with ethyl acetate and citric acid buffer (pH 6.0), and the extract was purified over a cation-exchange column (AG MP-50 resin). Detection was at 312 and 320 nm for QCT and DQCT, respectively, and at 320 nm for MQCA. The observed limit of detection for the 3 compounds was 0.025 microg/g in various tissues. The methods were linear over the concentrations range of 0.01-0.64 microg/mL with mean recoveries of approximately 71-86% and relative standard deviations of about 4-12% at the levels of 0.05, 0.10, and 0.20 microg/g. The method is highly selective and can be applied to the determination of QCT and its main metabolites in animal tissues, which would accelerate the pharmacokinetic and residue study of QCT in food animals.