Yamagaki Tohru, Suzuki Hiroaki, Tachibana Kazuo
Department of Chemistry, School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan.
Anal Chem. 2005 Mar 15;77(6):1701-7. doi: 10.1021/ac040150i.
Cross-ring cleavage ions produced by in-source decay (ISD), as well as deprotonated molecular ions [M - H]-, are invariably observed in negative-ion linear-mode matrix-assisted laser desorption/ionization time-of-flight mass spectrometry spectra of neutral oligosaccharides with 9H-pyrido[3,4-b]indole (norharman) as a matrix. The patterns of ISD ions depend on the oligosaccharide linkage type; thus, these ions are potentially useful in linkage analysis. In postsource decay (PSD) spectra from chlorinated molecular ions [M + Cl]-, all PSD ions are observed in the deprotonated form, although no deprotonated molecular ions are detected. In oligosaccharides having an alditol at the reducing end, deprotonated molecular ions [M - H]- are clearly seen in linear-mode mass spectra and survive in the PSD measurements. These results indicate that the deprotonation process drives ISD and PSD of oligosaccharides and that keto-enol tautomerization at the reducing terminal promotes ISD and PSD processes.
在以9H-吡啶并[3,4-b]吲哚（去甲哈尔满）为基质的中性寡糖负离子线性模式基质辅助激光解吸/电离飞行时间质谱图中，总能观察到由源内衰变（ISD）产生的跨环裂解离子以及去质子化分子离子[M - H]-。ISD离子的模式取决于寡糖的连接类型；因此，这些离子在连接分析中可能有用。在氯化分子离子[M + Cl]-的源后衰变（PSD）光谱中，尽管未检测到去质子化分子离子，但所有PSD离子均以去质子化形式被观察到。在还原端具有糖醇的寡糖中，去质子化分子离子[M - H]-在线性模式质谱中清晰可见，并在PSD测量中得以保留。这些结果表明，去质子化过程驱动了寡糖的ISD和PSD，并且还原端的酮-烯醇互变异构促进了ISD和PSD过程。
