Identification of human milk oligosaccharide positional isomers by combining IMS-CID-IMS and cryogenic IR spectroscopy

High-resolution ion mobility spectrometry (IMS) coupled with cryogenic infrared spectroscopy has proven to be a powerful technique for the identification of oligosaccharides. However, the need for an extensive database, combined with the scarcity of pure standards, remains a significant barrier to the broad application of this approach. To solve this issue, we demonstrate a method in which ion fragments produced by collision-induced dissociation (CID) are separated using IMS and identified using the vibrational fingerprints of only a few standards. Identification of the fragments allows us to determine the structure of the precursor molecule, the vibrational fingerprint of which is then added to our database. We then show how we can use this approach to identify the structure of mobility separated isomers found in pooled human milk.