Abstract: Two kinds of flavonoids from Sophora Flavecens Aits, dihydroflavonoids and dihydroflavonols, were studied by using electrospray ionization tandem mass spectrometry(ESI-MSⁿ). [M-H]^- of these two kinds of flavonoids were observed in the negative ion mode under ESI conditions, which provided us the molecular weights of them. Cross-ring reactions, arisen from MS² spectra of both dihydroflavonoids and dihydroflavonols, gave the fragment ions by the loss of neutral species. The differences of their cleavage positions were then proposed, dihydroflavonoids cleave at C2—O bond and C4—C10 bond, but dihydroflavonols cleave at C2—O bond and C3—C4 bond. The loss of neutral species from dihydroflavonoids and dihydroflavonols were also discussed, the former were several relative big neutral species, while the latter were some small species, such as CO, CO₂, H₂O and B-ring. The differences between dihydroflavonoids and dihydroflavonols were mainly arisen by hydroxy group at C-3 of the C-ring, which were the characteristic for dihydroflavonoids and dihydroflavonols under the ESI-MS n conditions.

Key words: Electrospray ionization tandem mass spectrometry, Dihydroflavonoids, Dihydroflavonols, Sophora Flavecens Aits