Determination of thyreostat residues from bovine matrices using high-performance liquid chromatography

High-performance liquid chromatography (HPLC) methodologies were evaluated for the detection and quantification of thyreostatic drug residues in cattl e serum and thyroid tissue. The paper details a protocol, using a simple et hyl acetate extraction for the determination of thiouracil, tapazole, methy l thiouracil, propyl thiouracil and phenyl thiouracil in thyroid tissue. Us ing two sequential HPLC injections, and quantitative analysis, in two steps , all five thyreostats were detectable at concentrations greater than 2.45- 4.52 ng/g. Modifications to a published method for detection of thyreostati c residues in serum involving the addition of mercaptoethanol and a freezin g step are described. The modifications improved sensitivity and allowed de tection of the five thyreostats at levels greater than 16.98-35.25 ng/ml. Y oung bulls were treated with thyreostats to demonstrate the validity of the methodologies described. Administered thyreostats were not absorbed equall y by the test animals and the compounds were not all detected in the serum samples removed at 7 days following drug withdrawal. These experiments indi cate the necessity to be able to detect thyreostat residues in a variety of matrices. (C) 1998 Elsevier Science B.V. All rights reserved.