Negative ion desorption chemical ionization mass spectrometry of flavonoid glycosides

Abstract

Negative ion mass spectra of underivatized flavonoid O- and C-glycosides were recorded using desorption chemical ionization (DCI) at a low reagent gas pressure. Advantages and limitations of the method for the characterization of the mono-, di- and triglycosides are discussed. For all O-glycosides investigated, the aglycone moieties are found to be base anions. The molecular masses of the glycosides are indicated by the presence of [M]−. ions with fairly high abundances for monoglycosides, lower abundances for diglycosides and a very low intensity for triglycosides. In addition to the sugar moiety losses, anions which resulted from the stepwise elimination of water from the sugar moiety were also observed at m/z 290 or 306 in 1 6 linked bioses, m/z 127, 145 and 163 in deoxyhexose as well as m/z 161 and 143 in hexose. Those ions except ions due to the molecule and the retro-Diels–Alder cleavage of the aglycone moiety could not be found in electron ionization mass spectra. Consequently, information concerning the structure of the aglycone moiety could be obtained using the EI technique and of sugar moiety using the negative ion DCI technique; also the combined positive and negative ion was shown to be a good approach for the structural characterization of flavonoid glycosides.