Determination of thyreostats in bovine urine and thyroid glands by HPLC–MS/MS

The use of thyreostats in livestock is strictly forbidden by European legislation since 1981. The investigation of thyreostats is commonly performed by their detection as derivatives with 3-iodobenzylbromide. Although it has advantages, the derivatisation procedure can generally cause a decrease in analyte concentrations. With the aim of simplifying the analysis of five thyreostats in both bovine urine and in thyroid glands, two methods were developed without the derivatisation step. Salting-out assisted liquid–liquid extraction was carried out for both matrices, followed by high-performance liquid chromatography coupled with triple-quadrupole mass spectrometry analysis. The methods were validated in agreement with the guidelines of Commission Decision 2002/657/EC. For all the thyreostats evaluated, satisfactory results were achieved; the recovery was within 96–104 % for both the matrices, while precision (coefficient of variation) was less than 20 % for urine and 21 % for thyroid glands. The limits of decision and capacities of detection for all the compounds were lower than the recommended values of 10 μg L−1 and 10 μg kg−1, respectively. In urine, the limits of decision ranged from 6.9 to 7.3 μg L−1, and the capacities of detection ranged from 8.5 to 9.7 μg L−1, while in thyroid glands these values varied from 6.6 μg kg−1 to 7.4 μg kg−1 and from 8.0 μg g−1 to 9.7 μg kg−1, respectively. The results obtained show that the methods described are suitable for the direct detection of thyreostats in bovine urine and thyroid glands.