Effective separation of carbohydrate isomers using metal cation and halogen anion complexes in trapped ion mobility...

Comprehensive analysis of carbohydrates, one of the critical steps towards the fundamental understanding of biological systems, has been hindered by the identifications of their complex isomeric structures differing in monosaccharide constituents, linkage positions, and configurations. While ion mobility spectrometry-mass spectrometry (IMS-MS) based methods have shown their utilities in performing glycomics measurements, there is still a lack of analytical methods allowing effective isomeric carbohydrate separation. Here, we systematically investigated the effect of alkaline earth cations (Ca²⁺ and Ba²⁺) and halogen anions (Cl^-, Br^- and I^-) addition on the separation of 21 pairs of isomeric oligosaccharides using trapped ion mobility spectrometry-mass spectrometry (TIMS-MS). [M + Ca + I]⁺ complex (M is an oligosaccharide) has shown experimentally to be the optimum complex for the separation of all 21 pairs of isomeric oligosaccharides used in this study with a calculated average resolution (r) ~ 1.82 and resolving power (R) ~ 100-150. The separation capability of this complex was further demonstrated by using mixtures of 15 oligosaccharides. The optimum [M + Ca + I]⁺ complex can be potentially used as an effective complex for enhancing the IMS separation resolution of isomeric carbohydrates.