FAST-ATOM-BOMBARDMENT MASS AND TANDEM MASS-SPECTRA OF PROTONATED AND ALKALI CATIONIZED ALDOBIOURONIC AND PSEUDOALDOBIOURONIC ACID PER-O-METHYL DERIVATIVES

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.