Fast atom bombardment mass and tandem mass spectra of protonated and alkali cationized aldobiouronic and pseudoaldobiouronic acid per‐O‐methyl derivatives

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The positive‐ion fast atom bombardment mass spectra of permethylated aldo‐ and pseudoaldobiouronic acids can be used to distinguish these classes of compounds. The collisional‐induced dissociation spectra of the [M + H]+ ions show fragment ions resulting from glycosidic bond cleavage and successive losses of methanol molecules. These spectra together with those of the [M + H  MeOH]+ oxonium ions allow the identification of the type of interglycosidic linkage. Collisional activation of the relatively stable [M + Na]+ ions show many fragmentations which are common to alkali cationized permethylated saccharides. Moreover, fragment ions resulting from two‐bond ring cleavage processes yield additional information with respect to the linkage between the hexose and uronic acid units.