Post-source decay mass spectrometry: optimized calibration procedure and structural characterization of permethylated oligosaccharides

✍ Scribed by Viseux, Nelly; Costello, Catherine E.; Domon, Bruno

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 244 KB
• Volume: 34
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(199904)34:4<364::aid-jms787>3.0.co;2-p

✦ Synopsis

Permethylated oligosaccharides were analyzed by matrix-assisted laser desorption/ionization mass spectrometry (MALDI/MS) using a reÑectron time-of-Ñight instrument in the post-source decay (PSD) mode. Under these ionization conditions, such derivatives yield intense signals corresponding to sodium or potassium cationized molecular species. Fragments observed in the PSD spectra result exclusively from cleavage of glycosidic bonds, preferentially at N-acetylhexosamine residues. A systematic study was carried out on a series of permethylated oligosaccharides to allow rationalization of the fragmentation processes. Fragments originating from both the reducing and the non-reducing ends of the oligosaccharide yield information on sequence and branching. Moreover, glycosyl residues linked in position 3 of HexNAc units give rise to a highly speciÐc elimination process, which allows unambiguous assignment of (1-3) interglycosidic linkages. Special attention was paid to the structural analysis of oligosaccharides carrying the commonly encountered fucosyl and sialyl end-caps. In the case of sialylated residues, a targeted methodology involving desialylation and speciÐc of the nascent free hydroxyl CD 3 -labeling groups was developed to mark the initial location of sialic acid residues along the oligosaccharide backbone. As accurate mass determination of fragment ions is essential for their assignment, a simpliÐed protocol for the calibration in the PSD mode is described. This procedure allows the determination of the correction function parameters required to process the data for an instrument that employs post-acceleration detection. MALDI/PSD-MS of permethylated oligosaccharides, by providing structural information at the low picomole level, appears to be a valuable complement, or an alternative, to the techniques currently in use for carbohydrate structural analysis.