Structural analysis of xyloglucan oligosaccharides by the post-source decay fragmentation method of MALDI-TOF mass spectrometry: Influence of the degree of substitution by branched galactose, xylose, and fucose on the fragment ion intensities

Highly branched xyloglucan oligosaccharides were analyzed by the post-sourc e decay (PSD) fragmentation method of matrix-assisted laser desorption / io nization time-of-flight mass spectrometry (MALDI-TOFMS), The ratio of [M-Xy l]+ and [M-Gal]+ fragment ion intensities could be used to characterize the degree of Gal substitution at the non-reducing end, because the number of possible chemical species was directly related to their relative ion intens ity. The intensity of the [M-Fuc]+ ion was predominantly strong in the frag ment spectrum of fucosyl oligosaccharides as the first fragmentation, indic ating the fucosyl linkage to be much weaker than the other glycosidic linka ges in the MALDI-PSD fragmentation, Setting fragment ion [M-Fuc]+ to the ps eudo precursor ion [MF]+, the second fragmentation ions were produced from [MF]+ in the drift region in PSD fragmentation of fucosyl oligosaccharides.