Tandem mass spectrometry of alkali cationized polysaccharides in a quadrupole ion trap

Quadrupole ion trap mass spectrometry is used to study the linkage type dependent dissociation pathways of alkali-cationized disaccharides, mostly of the type glucosyl(1 → X)glucose (X = 1, 2, 3, 4, or 6). The reaction mechanisms of a set of disaccharides containing all possible α anomeric linkage types and some β anomers are probed with tandem mass spectrometry, MSn, and double resonance experiments. Tandem mass spectrometry experiments on an 18O-labeled disaccharide show that the dissociation paths for Li and Na cationized species are the same. Experiments on three trisaccharides (isomaltotriose, maltotriose, and panose), a tetrasaccharide (isomaltotetraose), and a pentasaccharide (maltopentaose) show that tandem mass spectrometry provides all available linkage information and MSn can provide selected linkage information. The mode of alkali binding is examined via semiempirical calculations and by measuring alkali-carbohydrate relative cation affinities.