Investigating carbohydrate isomers by IMS-CID-IMS-MS: precursor and fragment ion cross-sections

Ion mobility spectrometry techniques (IMS and IMS-IMS) combined with collision-induced dissociation (CID) and mass spectrometry (MS) are used to investigate the structures of singly-lithiated carbohydrate isomers. With the exception of some favorable cases, IMS-MS analyses of underivatized carbohydrates reveal that most isobaric precursor ions have similar collision cross sections (ccs). In contrast, ccs values for isomeric fragment ions obtained by IMS-CID-IMS-MS analysis are often different, and thus appear to be useful as a means of distinguishing the isomeric precursors. We report values of ccs (in He) for precursor- and associated-fragment ions for three monosaccharide isomers (glucose, galactose and fructose), ten disaccharide isomers (sucrose, leucrose, palatinose, trehalose, cellobiose, β-gentiobiose, isomaltose, maltose, lactose and melibiose), and three trisaccharide isomers (raffinose, melezitose and maltotriose). These values are discussed as a means of differentiating precursor carbohydrates.