Analysis of Tetrahydro-β-carbolines and Their Precursors by Electron Ionization Mass Spectrometry. Identification in Foodstuffs by Gas Chromatography/Mass Spectrometry

Electron ionization (EI)-induced fragmentation was studied in 40 tetrahydro-β-carbolines, tryptamine and tryptophan derivatives. Tryptamine and tryptophan derivatives give the ion C9H8N+· (m/z 130) as the main fragment, accompanied by low-intensity molecular ions. Fragmentation in 1,2,3,4-tetrahydro-β-carbolines is dominated by the retro-Diels–Alder rearrangement that provides the ion C10H9N+· (m/z 143). The fragmentation of 1-methyl-1,2,3,4-tetrahydro-β-carbolines is dominated both by the loss of a methyl radical and by the retro-Diels–Alder fragmentation to give C11H11N++ (m/z 157). These compounds also exhibits an abundant molecular ion. 1-Ethyl-1,2,3,4-tetrahydro-β-carbolines lose the ethyl radical (M − CH2CH3) and also show an abundant M+·. N-Methoxycarbonyl and N-trifluoroacetyl volatile derivatives of tetrahydro-β-carbolines and their precursors allow the separation and identification of these compounds by GC/MS. 1,3-Disubstituted 1,2,3,4-tetrahydro-β-carbolines give rise to two diastereoisomers (1S,3S) and (1R,3S) which are resolved by the GC/MS and provide similar mass spectra. The presence of 1-methyl-1,2,3,4-tetrahydro-β-carboline-3-carboxylic acid in foodstuffs (beer and orange juice) was demonstrated by GC/MS of its N-methoxycarbonyl methyl ester derivative. It is suggested that diet could be a source of tetrahydro-β-carbolines in mammals.