B. Lebizec et al., DETECTION AND IDENTIFICATION OF THYREOSTATS IN THE THYROID-GLAND BY GAS-CHROMATOGRAPHY MASS-SPECTROMETRY, Analytica chimica acta, 340(1-3), 1997, pp. 201-208
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.