Structural analysis of oligosaccharides by atmospheric pressure matrix-assisted laser desorption/ionisation quadrupole ion trap mass spectrometry.

An ion source incorporating a fibre optic interface has been constructed for atmospheric pressure matrix-assisted laser desorption/ionisation quadrupole ion trap mass spectrometry. The configuration has been applied to the study of linear and complex oligosaccharides. Multi-stage tandem mass spectrometry (MSn, n = 2-4) experiments carried out in the ion trap enable extended fragmentation pathways to be investigated that yield structural information. Collisional activation of sodiated oligosaccharides, as demonstrated on the model compound maltoheptaose, produces primarily B and Y fragments resulting from cleavage of glycosidic bonds; fragments from cross-ring cleavages are also observed following further stages of tandem mass spectrometry, providing additional linkage information. The analyses of mixtures of complex oligosaccharides are demonstrated for N-linked glycans from chicken egg glycoproteins and a ribonuclease glycan mixture. Mass spectrometric and tandem mass spectrometric data for sugars with molecular weights up to 4000 Da is shown for mixtures of linear dextrans and N-linked glycans. The use of MSn (n = 3, 4) on these complex molecules enabled structural information to be elucidated that confirms data observed in the MS/MS spectra.