A New Strategy Coupling Ion-Mobility-Selective CID and Cryogenic IR Spectroscopy to Identify Glycan Anomers

Determining the primary structure of glycans remains challenging due to their isomeric complexity. Whilehigh-resolution ion mobility spectrometry (IMS) has recentlyallowed distinguishing between many glycan isomers, the arrival-time distributions (ATDs) frequently exhibit multiple peaks, whichcan arise from positional isomers, reducing-end anomers, ordifferent conformations. Here, we present the combination ofultrahigh-resolution ion mobility, collision-induced dissociation(CID), and cryogenic infrared (IR) spectroscopy as a systematicmethod to identify reducing-end anomers of glycans. Previousstudies have suggested that high-resolution ion mobility of sodiated glycans is able to separate the two reducing-end anomers. In thiscase, Y-fragments generated from mobility-separated precursor species should also contain a single anomer at their reducing end. Weconfirm that this is the case by comparing the IR spectra of selected Y-fragments to those of anomerically pure mono- anddisaccharides, allowing the assignment of the mobility-separated precursor and its IR spectrum to a single reducing-end anomer. Theanomerically pure precursor glycans can henceforth be rapidly identified on the basis of their IR spectrum alone, allowing them to be distinguished from other isomeric forms