A rapid method for determination and confirmation of the thyreostats in milk and urine by matrix solid-phase dispersion and gas chromatography-mass spectrometry

A rapid and simple method for determination and confirmation of the thyreostats in milk and urine has been developed. The samples were extracted and purified by matrix solid-phase dispersion (MSPD) with silica gel as the solid support, and the thyreostats including tapazole, 2-thiouracil, 6-methyl-2-thiouracil, 6-propyl-2-thiouracil and 6-phenyl-2-thiouracil have been separated and detected by gas chromatography-mass spectrometry in selected ion mode with dimethylthiouracil as internal standard after derivatization with pentafluorobenzylbromide and N-methyl-N-(trimethylsilyl)-trifluoroacetamide. The derivatization reaction was conducted in a strong basic condition, which can improve the derivatization yields of the thyreostats in the presence of the matrix. The relative abundances of the selected ions in the chromatograms of the derivatives were stable and consistent, and can be used for the confirmatory purpose. The average recoveries of the five thyreostatic compounds in milk and urine were above 70% in most cases with the relative standard deviations between 2.1 and 7.9%. The limit of detection was 0.0016 μg g−1 for the thyreostats except for that of tapazole, which was 0.004 μg g−1.