DETECTION AND IDENTIFICATION OF THYREOSTATS IN THE THYROID-GLAND BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY

Because thyreostatic compounds, also named thyreostats, are banned in Europe (directive 86/469/EEC), methods have to be developed to prevent the illegal use of these substances. The analytical procedure describ ed herein involves the detection and identification at the low ng g(-1 ) level of the main thyreostats known to be used for growth promotion by gas chromatography coupled to mass spectrometry (GC-MS). The assay is based on a liquid/liquid extraction of the thyroid gland, derivatiz ation with pentafluorobenzyl bromide (PFBBr), purification on a silica solid phase extraction column and finally a trimethylsilylation prior to GC-MS. Good thyreostat recoveries were obtained (from 40% to 70%) as well as at acceptable repeatability. The target analytes were detec table below the 1 ng g(-1) level on a quadrupole mass spectrometer wit h negative chemical ionization (NCI) using ammonia as reagent gas and the selected ion monitoring (SIM) acquisition mode. This limit of dete ction was also reached in the SIM high resolution mode. An improved sp ecificity (more diagnostic ions) was obtained under electronic impact (EI) conditions and positive chemical ionization (PCI) with methane as reagent gas. Identification of thyreostats according to the EU (Europ ean Union) criteria (93/256/EEC decision) was made on the basis of two independent GC-MS techniques; the limit of identification was close t o 5 ng g(-1) for most thyreostats, which represents a real improvement for their control.