Fingerprinting of Underivatized Monosaccharide Stereoisomers Using High-Resolution Ion Mobility Spectrometry and Its Implications for Carbohydrate Sequencing.

Although carbohydrates are the most abundant biopolymers on Earth, there is currently no streamlined method to elucidate their complete sequence. Mass spectrometry (MS) alone is blind to many cases of isomerism and thus gives incomplete information for carbohydrates. Notably, the coexistence of numerous stereoisomeric monosaccharide subunits is of special concern. Over the last 10 years, the coupling of ion mobility spectrometry (IMS) with MS has kept gaining momentum─especially with the advent of high-resolution (HR) IMS devices such as cyclic IMS (cIMS). In fact, IMS is sensitive to the gas-phase conformations of molecules and, thus, to stereoisomerisms. In this article, we present innovative ion mobility methods on a cIMS instrument that allowed us to build a database of HR-IMS fingerprints for various underivatized monosaccharide stereoisomers. The conditions were fully compatible with MS/MS fragmentation approaches. We further verify that these fingerprints afford the identification of monosaccharidic fragments released upon collisional fragmentation of oligosaccharides. Overall, these results pave the way toward direct sequencing of carbohydrates at the monosaccharide level using HR-IMS.