SODIUM-CATIONIZED OLIGOSACCHARIDES DO NOT APPEAR TO UNDERGO INTERNAL RESIDUE LOSS REARRANGEMENT PROCESSES ON TANDEM MASS-SPECTROMETRY

The phenomenon of 'internal residue loss' of protonated native- and pe r-O-methylated oligosaccharides has recently been described as occurri ng on high-energy collision conditions. Awareness of this phenomenon i n the mass spectrometric analysis of oligosaccharides is of great impo rtance since the rearrangement ions produced by this process may compl icate monosaccharide sequence assignment. In this research, oligosacch arides having N-acetyl glucosamine residues as the reducing or non-red ucing terminal residue have been included in our MS/MS analyses in ord er to try to better understand the factors that influence 'internal re sidue loss'. Native and per-O-methylated compounds were submitted to p ositive and negative MS/MS, selecting protonated, sodium cationized, o r de-protonated pseudomolecular ions as precursors. High- and low-ener gy collision induced dissociation tandem mass spectrometry experiments were performed using a Pour sector instrument and a hybrid quadrupole time-of-flight mass spectrometer respectively. The phenomenon of 'int ernal residue loss' was not observed on either high- or low-energy CID -MS/MS when sodium-cationized precursor ions of either native or per-O -methylated oligosaccharides were examined. Similarly, MS/MS analysis performed in the negative ionization mode also failed to generate ions resulting from 'internal residue loss'. This combination of experimen ts therefore offers a way to be sure whether ions observed in the tand em mass spectra of protonated native or per-O-methylated oligosacchari des originate from 'internal residue loss' or from direct glycosidic l inkage fragmentation. (C) 1998 John Wiley & Sons, Ltd.