Gas-liquid chromatographic determination of levamisole residues in bovine milk.

A gas-liquid chromatographic (GLC) method is described for determining residues of levamisole, (1-)-(2,3,5,6-tetrahydro-6-phenylimidazo [2,1-b] thiazole), in milk. Levamisole is extracted from an alkaline milk sample with water-saturated ethyl acetate. After co-extractives are removed by various partitionings, the levamisole concentration is measured by GLC by using an alkali (RbSO4) flame ionization detector, vs. an external standard. This method is satisfactory for determining levamisole residues as low as 0.01 ppm in bovine milk. Apparent residues in control milk samples averaged less than 0.001 ppm. Recoveries of 0.01-2.0 ppm added levamisole ranged from 86.5 to 113%. Animals treated with various Tramisol formulations showed apparent levamisole residues below the validated sensitivity of the method (0.01 ppm) at sampling periods exceeding 48 hr.