Thyreostatic drugs, illegally administrated to livestock for fattening purposes, are banned in the European Union since 1981 (Council Directive 81/602/EC). For monitoring their illegal use, sensitive and specific analytical methods are required. In this study an UHPLC-MS/MS method was described for quantitative analysis of eight thyreostatic drugs in urine, this without a derivatisation step. The sample pretreatment involved a reduction step with dithiothreitol under denaturating conditions at 65 degrees C, followed by liquid-liquid extraction with ethyl acetate. This analytical procedure was subsequently validated according to the EU criteria (2002/657/EC Decision), resulting in decision limits and detection capabilities ranging between 1.1 and 5.5 microg L(-1) and 1.7 and 7.5 microg L(-1), respectively. The method obtained for all, xenobiotic thyreostats, a precision (relative standard deviation) lower than 15.5%, and the linearity ranged between 0.982 and 0.999. The performance characteristics fulfill not only the requirements of the EU regarding the provisional minimum required performance limit (100 microg L(-1)), but also the recommended concentration fixed at 10 microg L(-1) in urine set by the Community of Reference Laboratories. Future experiments applying this method should provide the answer to the alleged endogenous status of thiouracil.
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