25 負イオンMALDI質量分析法による中性糖鎖の構造解析(口頭発表の部)

抄録

Structure analyses of underivatized neutral oligosaccharides are systematically performed by UV matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI TOF MS) and UV-MALDI ion-trap time-of-flight mass spectrometry (ion-trap/TOF MS) acquired in negative-ion mode. Interestingly their fragmentation significantly differ each other. In postsource decay (PSD) in UV-MALDI TOF MS, cross-ring cleavage at the reducing terminal predominates. On the other hand, glycosyl bond cleavage (C-type fragmentation) takes place preferentially in collision induced dissociation (CID) in UV-MALDI ion-trap/TOF MS. The cross-ring cleavage in PSD similar to that in in-source decay occurs via a non-ergodic path characteristic of the UV-MALDI process itself. During ion-trap/TOF MS experiments the deprotonated molecular ions survive during several tens of milliseconds after CID event because the high internal energy chlorinated precursor ions are cooled by collisional cooling in the ion trap. The results obtained suggest that: the PSD from the chlorinated precursor ion in UV-MALDI TOF MS might proceed as a two-step reaction; in the first, a high internal energy deprotonated molecular ion is generated as a reaction intermediate during the flight in the drift tube, and in the second, the rapid decomposition from the deprotonated molecular ion takes place.