title: Gas chromatographic determination of residues of thyreostatic drugs in bovine muscle tissue using combined resin mediated methylation and extraction.
abstract: A method is described for the assay of residues of the thyreostatic substances 2-thiouracil, 6-methyl-2-thiouracil, 5- and 6-propyl-2-thiouracils and 6-phenyl-2-thiouracil in beef muscle at levels of quantitation down to 25 microg/kg for thiouracil and 15 microg/kg for substituted thiouracils. Analytes are extracted from the muscle matrix with acetonitrile and methylated by absorption onto a macroporous anion exchange resin followed by treatment with methyl iodide in acetonitrile at room temperature. Supercritical carbon dioxide is also a suitable derivatization solvent. Determination is carried out using gas chromatography with mass spectrometric detection. The methyl ester of 2,4,5-trichlorophenoxyacetic acid serves as an internal standard while 5-methyl-2-thiouracil is a suitable surrogate. 5-Ethyl-2-thiouracil is added to minimise losses of the analytes during the analysis. The method exhibits a linear range of 25-625 microg/kg for the substituted thiouracils and 50-1250 microg/kg for 2-thiouracil. Recovery of the analytes ranges from 50% for 6-phenyl-2-thiouracil to 90% for 2-thiouracil with coefficients of variation of less than 10%.
authors.affiliation: Australian Government Analytical Laboratories, Pymble, NSW.
authors.forename: G Y
authors.initials: GY
authors.lastname: Yu
authors.forename: E J
authors.initials: EJ
authors.lastname: Murby
authors.forename: R J
authors.initials: RJ
authors.lastname: Wells
mesh_terms: D000818:Animals; D013956:Antithyroid Agents / Q000032:analysis* / Q000737:chemistry; D002417:Cattle; D004350:Drug Residues / Q000032:analysis*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods*; D016014:Linear Models; D008745:Methylation; D009132:Muscles / Q000737:chemistry*; D009994:Osmolar Concentration; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013889:Thiouracil / Q000032:analysis* / Q000737:chemistry
chemical_list: D013956:Antithyroid Agents; D013889:Thiouracil