Structural Characterization of Disaccharides Using Cyclic Ion Mobility Spectrometry and Monosaccharide Standards

To understand the mode of action of bioactive oligosaccharides, such as prebiotics, in-depth knowledge about all structural features, including monosaccharide composition, linkage type, and anomeric configuration, is necessary. Current analytical techniques provide limited information about structural features within complex mixtures unless preceded by extensive purification. In this study, we propose an approach employing cyclic ion mobility spectrometry (cIMS) for the in-depth characterization of oligosaccharides, here demonstrated for disaccharides. We were able to separate galactose and glucose anomers by exploiting the high ion mobility resolution of cIMS. Using the obtained monosaccharide mobilograms as references, we determined the composition and anomeric configuration of 4β-galactobiose by studying the monosaccharide fragments generated by collision-induced dissociation (CID) before the ion mobility separation. Drift times and individual MS² spectra of partially resolved reducing-end anomers of 4β-galactobiose, 4β-galactosylglucose (lactose), and 4β-glucosylglucose (cellobiose) were obtained by deconvolution using CID fragmentation induced in the transfer region between the cIMS cell and TOF analyzer. The composition and anomeric configuration of the reducing end anomers of these disaccharides were identified using cIMS² approaches, where first each anomer was isolated using cIMS and individually fragmented, and the monosaccharide fragments were again separated by cIMS for comparison with monosaccharide standards. With these results we demonstrate the promising application of cIMS for the structural characterization of isomeric oligosaccharides.