A sensitive method for the determination of novel derivatised thyrostat residues in urine by using UHPLC-MS/MS

Thyrostats increase water retention and absorption in animals; this property is abused in the rearing of meat producing animals to inflate carcase weight in a bid to increase the profits of producers. As such meat is of poor quality, and due to the potential carcinogenic and teratogenic properties of thyrostats, their use has been banned in the EU since 1981. The difficulties encountered in the analysis of these compounds, due to their small size, high polarity, and the endogenous nature of some analytes (2-thiouracil, 4-thiouracil, 5-methylthiouracil), has limited the sensitivity of methods in difficult matrices such as urine, with minimum method performance requirements (MMPR) of 10 µg L^-1 for six analytes (2-thiouracil, 5-methylthiouracil, propylthiouracil, tapazole/methimazole, benzylthiouracil and mercaptobenzimidazole). This work describes the development and alternative factorial validation, to the criteria as set out in CIR (EU) 2021/808, of a rapid and sensitive method for the quantitative confirmation of 11 thyrostats, including the endogenous analytes, using an extracted solvent standard calibration curve and post column infusion of NH₄F, with decision limit (CCα) values ranging from 0.29 to 0.51 µg L^-1.