COMPARISON OF FRAGMENTATION MODES FOR THE STRUCTURAL DETERMINATION OFCOMPLEX OLIGOSACCHARIDES IONIZED BY MATRIX-ASSISTED LASER DESORPTION IONIZATION MASS-SPECTROMETRY/

Fragment ions from underivatized N-linked oligosaccharides ionized by matrix-assisted laser desorption/ionization mass spectrometry were obt ained by spontaneous fragmentation on a magnetic sector mass spectrome ter, by post-source decay (PSD) on a reflectron time-of-flight (TOF) i nstrument and by collision induced dissociation on a magnetic sector i nstrument fitted with an orthogonal-TOF analyser, Spontaneous fragment ation on the magnetic sector instrument produced ions mainly by glycos idic cleavage together with two abundant ions formed by cross-ring cle avage of the reducing-terminal residue. The PSD spectra were similar, the majority of ions being formed by glycosidic cleavage. Internal fra gment ions were abundant. High-energy collision-induced dissociation s pectra, recorded with the orthogonal-TOF analyser, differed considerab ly from the other types of spectra, particularly in the appearance of major fragment ions produced by cross-ring cleavages of most of the co nstituent monosaccharide residues. These ions allowed much sequence an d branching information to be obtained from the oligosaccharide.