GAS-CHROMATOGRAPHIC DETERMINATION OF RESIDUES OF THYREOSTATIC DRUGS IN BOVINE MUSCLE-TISSUE USING COMBINED RESIN MEDIATED METHYLATION AND EXTRACTION

A method is described for the assay of residues of the thyreostatic su bstances 2-thiouracil, 6-methyl-2-thiouracil, 5- and 6-propyl-2-thiour acils and 6-phenyl-2-thiouracil in beef muscle at levels of quantitati on down to 25 mu g/kg for thiouracil and 15 mu g/kg for substituted th iouracils. Analytes are extracted from the muscle matrix with acetonit rile and methylated by absorption onto a macroporous anion exchange re sin followed by treatment with methyl iodide in acetonitrile at room t emperature. Supercritical carbon dioxide is also a suitable derivatiza tion solvent. Determination is carried out using gas chromatography wi th mass spectrometric detection. The methyl ester of 2,4,5-trichloroph enoxyacetic acid serves as an internal standard while 5-methyl-2-thiou racil is a suitable surrogate. 5-Ethyl-2-thiouracil is added to minimi se losses of the analytes during the analysis. The method exhibits a l inear range of 25-625 mu g/kg for the substited thiouracils and 50-125 0 mu g/kg for 2-thiouracil. Recovery of the analytes ranges from 50% f or 6-phenyl-2-thiouracil to 90% for 2-thiouracil with coefficients of variation of less than 10%. (C) 1997 Elsevier Science B.V.