ANALYSIS OF BETA-AGONISTS IN URINE AND TISSUES BY CAPILLARY GAS CHROMATOGRAPHY-MASS SPECTROMETRY - IN-VIVO STUDY OF SALBUTAMOL DISPOSITION IN CALVES

The fate of salbutamol sulphate given orally has been investigated in calves. The urinary excretion rate and the tissue distribution of this beta-agonistic drug were studied by capillary gas chromatography coup led to low resolution mass spectrometry (GC-LRMS) under electron impac t (EI) ionization mode, using an hexadeuterated salbutamol analogue as the internal standard. The parent drug and metabolites were extracted via solid phase extraction (SPE) mixed-phase-containing disposable co lumns and analysed as their trimethylsilyl derivatives. A more efficie nt clean-up had to be carried out for tissue samples. An acidic precip itation followed by a liquid-liquid extraction were therefore performe d before the SPE. Moreover, the problem of tissue digestion was elucid ated by means of an ultrasonic probe. Samples were also analysed befor e and after enzymic hydrolysis using purified beta-glucuronidase and a mixture of beta-glucuronidase and arylsulphatase, to obtain evidence of phase II conjugation mechanisms. Both free salbutamol and conjugate d metabolites were detected in urine and tissue samples. Except for li ver or kidney, salbutamol was rapidly cleared from most tissues after a withdrawal period. The possible excretion of some phase I metabolite s was also investigated, using further analyses under positive chemica l ionization LRMS and high resolution mass spectrometry (HRMS).