Fragmentation study of globularin through positive and negative ESI/MS, CID/MS, and tandem MS/MS

The structure of globularin was studied by a mass spectrometric methodology based on the combined use of positive and negative electrospray ionization, collision-induced dissociation (CID), and tandem mass spectrometry. The mass spectrometry investigation was achieved through in-source fragmentation of the deprotonated [M - H](-), protonated [M + H](+), lithiated [M + Li](+), sodiated [M + Na](+), and potassium-cationized [M + K](+) ions. This allowed collision-induced dissociation spectra of the ionized molecular ions to be obtained to give valuable structural information regarding the nature of both the glycoside and the aglycone moieties and the effect of metal cationizationon the CID spectra. Glycosidic fission and ring cleavages of both aglycone and sugar moieties were the major fragmentation pathways observed during collision-induced dissociation, where the losses of small molecules, the cinnamoyl and the cinnamate parts were also observed. Alkali metal cationization offers additional fragmentation pathways involving cross rings cleavage under CID conditions. Unlike the dissociation of protonated molecular ions, that of metal-cationized molecules also provides sugar fragments where the C-0(+) fragment corresponding with the glucose ion was obtained as a major daughter peak for all the studied compounds. Even with low abundance, fragment ions coordinated to K+ were also observed from [M + K](+).