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Electrospray operated in the negative mode was used to analyse methoxylated flavonoids. They were found to produce radical anions by collision-induced fragmentation of the aglycones. Loss of a methyl group from the deprotonated molecule corresponding to M - H - 15-* ions, as well as M - H - 15-28-* and M - H - 15-29- fragment ions, were found to constitute the characteristic fragmentation for the monomethoxylated species, whereas M - H - 15-*, M - H - 30- and M - H - 30-28- were predominant for the polymethoxylated species. Obtained under similar conditions, the product-ion spectra of isomeric compounds were characteristically different. It is therefore possible to distinguish between methoxylated flavonoids with identical molecular mass, e.g. when screening plant extracts for flavonoid composition. However, comparison with standard compounds is necessary for the identification of unknown flavonoid aglycones.
Ulla Justesen (2001) studied this question.