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Flavonoids are ubiquitous molecules in nature and are found in almost all plants, including fruits and vegetables. Although flavonoids are structurally similar, subtle differences in their structures lead to important changes in their biological activities. Over years, mass spectrometry has become an ideal tool for the characterization of those important molecules. In particular to overcome the challenge of structure assignment, tandem mass spectrometry was used in numerous studies. In the present study, we submitted selected flavonoid 7- O-diglycosides to electrospray ionization to prepare different kinds of flavonoid ions, i.e. protonated, sodium- cationized and copper-cationized molecules. Most of the investigated reactions are already described in the literature in several papers and the aim of the present study is to present concise and coherent relations between CID reactions, cationizing agents and flavonoid 7-O-diglycoside structures. Some insights in the reaction mechanisms and the role of the cationizing particles will also be attempted.

Differentiation of flavonoid congeners remains a challenging analytical problem and confirming the structures of the different isomers is difficult, even when they can be adequately separated from mixtures. In the present report, in order to overcome the limits of our recently proposed method that relies on the distinctive CID behaviors of [(flavonoid - H(+)) + Cu(2+)] complexes to obtain direct structural evidences, we decided to investigate the possibility of using Pb(II) complexation to generate significant differences upon CID. We selected five flavonoid diglycosides with targeted structural features to estimate the applicability of this methodology. Electrospray ionization from methanol-not acetonitrile-solutions was advantageously used for preparing the [(flavonoid diglycoside - H(+)) + Pb(2)+](+) complexes. Upon collisional activation, [(flavonoid diglycoside- H(+)) + Pb(2+)](+) ions mainly dissociate by glycosidic bond cleavage. Nevertheless, specific cross-ring cleavages are also induced and lead to a clear-cut determination of (i) the nature of the disaccharide group, i.e. rutinose or neohesperidose, (ii) the nature of the aglycone part, flavanone or flavone and (iii) the relative position of the disaccharide substituent on the aglycone part, i.e. 3-O- vs 7-O positions.

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