Online Separation and Identification of Isomers Using Infrared Multiple Photon Dissociation Ion Spectroscopy Coupled to Liquid Chromatography: Application to the Analysis of Disaccharides Regio-Isomers and Monosaccharide Anomers.

The vast array of molecular isomerisms which form the complex molecular structure of carbohydrates is the foundation of their biological versatility but defies the analytical chemist. Hyphenations of mass spectrometry with orthogonal structural characterization, such as ion mobility or ion spectroscopy, have recently shown great promise for distinction between closely related molecular structures. Yet, the lack of analytical strategies for identification of isomers present in mixtures remains a major obstacle to routine carbohydrate sequencing. In this context, an ideal workflow for glycomics would combine isomer separation and individual characterization of the molecular structure with atomistic resolution. Here we report the implementation of such a multidimensional analytical strategy, which consists of the first online coupling of high-performance liquid chromatography (HPLC)-MS and infrared multiple photon dissociation (IRMPD) spectroscopy. The performance of this novel workflow is exemplified in the case of monosaccharides (anomers) and disaccharides (regioisomers) standards. We report that the LC-MS-IRMPD approach offers a robust advanced MS diagnostic of mixtures of isomers, including carbohydrate anomers, which is critical for carbohydrate sequencing. Our results also explain the bimodal character generally observed in LC chromatograms of carbohydrates. More generally, this multidimensional analytical strategy opens the gateway to rapid identification of molecular isoforms with potential application in the "omics" fields.