Mass Spectrometry of Labelled Triterpenoids: Thermospray and Electron Impact Ionization Analysis

Abstract

The mass spectra of unlabelled and specifically labelled triterpenes and derivatives were recorded using thermospray liquid chromatography (TSP-LC) and electron impact (EI) ionization. These mass spectra were used for the development of assays to characterize the products from the in vitro oxidative biodegradation of triterpenoids and the identification of compounds in plant extracts. Analysis using gas chromatography—mass spectrometry (GC—MS) with EI ionization of the free products, acetates and trimethylsilyl derivatives, showed lower limits of detection and higher selectivity compared with those with TSP-LC ionization. TSP-LC ionization may be useful for the determination of the molecular ions of highly oxygenated tritepenoids. Accurate masses of the EI fragment ions were recorded for triterpenes of the lupane series and fragmentation routes are discussed. Based on these characteristic fragmentations, O-methyl-β-lupeol has been identified in plant extracts from Orbygnia species.