Analysis of a series of isomeric oligosaccharides by energy-resolved mass spectrometry: a challenge on homobranched trisaccharides.

Glycans exist as part of glycoproteins and glycolipids, which are involved in a variety of biological functions. The analysis of glycan structures, particularly that of structural isomers, is fundamentally important since isomeric glycans often show distinct functions; however, a method for their structural elucidation has not yet been established. Anomeric configurations, linkage positions and branching are the major factors in glycans and their alteration results in a large diversity of glycan structures. The analysis of vicinally substituted oligosaccharides is extremely difficult because the product ions formed in tandem mass spectrometry (MS/MS) often have the same m/z values. In our endeavor to address the issue, we analyzed a series of homo-substituted trisaccharides consisting only of glucose by collision-induced dissociation (CID), especially energy-resolved mass spectrometry (ERMS). It was found that these structurally related glycans could be distinguished by taking advantage of differences in their activation energies in ERMS.