Fragmentation characteristics of permethylated oligosaccharides using a matrix-assisted laser desorption/ionization two-stage time-of-flight (TOF/TOF) tandem mass spectrometer.

Matrix-assisted laser desorption/ionization two-stage time-of-flight (MALDI-TOF/TOF) tandem mass spectrometry (MS/MS) was applied to characterize permethylated oligosaccharides. Under these ionization conditions such derivatives yield intense signals corresponding to sodium-cationized molecular species. A systematic study was conducted on a series of neutral and sialylated permethylated oligosaccharides to allow rationalization of the fragmentation processes. The major fragments observed in the MALDI-TOF/TOF-MS/MS spectra result from cleavage of glycosidic bonds, preferentially at N-acetylhexosamine and sialic acid residues. The fragments originating from both the reducing and the non-reducing ends of the glycan yield information on sequence and branching. Cross-ring cleavages, which are very informative of the linkages of the monosaccharide residues constituting these oligosaccharides, and 'internal' cleavage ions which are derived from elimination of substituents from around the pyranose ring, were also observed. This extensive fragmentation was shown to be useful for the structural characterization of oligosaccharides. MALDI-TOF/TOF-MS/MS of permethylated oligosaccharides appears to be a powerful tool for carbohydrate structural analysis.