Determination of thyreostatic residues in cattle plasma by high-performance liquid chromatography with ultraviolet detection.

A procedure is described for the concurrent assay of thiouracil, methylthiouracil, propylthiouracil, phenylthiouracil and methimazole in bovine plasma. In this procedure, reversed-phase high-performance liquid chromatography is performed after liquid-liquid extraction of plasma with ethyl acetate. Compounds are quantified by ultraviolet detection using a wavelength of 276 nm for thiouracil, methylthiouracil, propylthiouracil and phenylthiouracil and 258 nm for methimazole. The linearity range, precision, recovery and detection limits were determined and the method was shown to be applicable to samples of plasma from young bulls experimentally treated with methylthiouracil.