Analytical Methods for Residues of Tetracyclines in the Liver of Swine

Abstract

Analytical methods for residual tetracyclines (TCs) in the liver of swine are discussed.Oxytetracycline (OTC) and chlortetracycline (CTC) were well extracted with 0.1% citric acid-ethyl alcohol (7:3) mixture, then absorbed on an Amberlite XAD-2 resin column and eluted with methyl alcohol. The eluate was concentrated to dryness and dissolved in phosphate buffer (pH 4.5) to prepare a test solution. The cup plating method with Bacillus cereus var. mycoides as the test organism was employed for the assay, and the average recoveries were 92.0% (OTC) and 84.0% (CTC). As little as 0.05μg/g (OTC) or 0.01μg/g (CTC) was detectable.The extraction and the column chromatography were carried out on samples spiked with other antibiotics in order to check the specificity of the present method. Kanamycin (5.0μg/g), tylosin (5.0μg/g), kitasamycin (5.0μg/g) or flavophospholipol (5.0μg/g) showed no inhibition zone when the final test solution was tested by the cup plating method, but penicillin G (0.03u/g), bacitracin (0.5u/g) or monensin (0.25μg/g) showed an inhibition zone.Bioautography was suitable for both separation and confirmation of the identity of TCs.