STRUCTURAL ELUCIDATION OF CLENBUTEROL-LIKE AND MABUTEROL-LIKE COMPOUNDS IN COMPLEX MATRICES USING SILYLATED AND N-BUTYLBORONATE DERIVATIVESBY GAS CHROMATOGRAPHY ELECTRON IMPACT AND CHEMICAL-IONIZATION MASS-SPECTROMETRY

The mass spectra as their trimethylsilyl ethers and boronated derivati ves under electron impact (EI) and methane chemical ionization conditi ons of seven unauthorized beta(2)-agonists found in cattle feed are pr esented. Structural elucidation was achieved through comparison with t he standards clenbuterol, mabuterol and mapenterol. The structures of brombuterol, bromoclenbuterol and bromomapenterol were deduced from th eir isotopic patterns. Examination of fragments of boronated mabuterol -like compounds under EI conditions involved the differentiation of tw o isobaric compounds, mabexerol and 3-methylmapenterol, The amino subs tituent of isopropylclenbuterol and isopropylbromoclenbuterol was obta ined from clenbuterol, as these molecules specially fragment with a ne utral dissociation of the side-chain, confirmed by tandem mass spectro metry on a triple-guadrupole instrument. The branching structure of is opropylclenbuterol was investigated by means of H-1 MMR experiments.