Distinguishing isomeric saccharides poses a major challenge
for
analytical workflows based on (liquid chromatography) mass spectrometry
(LC–MS). In recent years, many studies have proposed infrared
ion spectroscopy as a possible solution as the orthogonal, spectroscopic
characterization of mass-selected ions can often distinguish isomeric
species that remain unresolved using conventional MS. However, the
high conformational flexibility and extensive hydrogen bonding in
saccharides cause their room-temperature fingerprint infrared spectra
to have broad features that often lack diagnostic value. Here, we
show that room-temperature infrared spectra of ion-complexed saccharides
recorded in the previously unexplored far-infrared wavelength range
(300–1000 cm–1) provide well-resolved and
highly diagnostic features. We show that this enables distinction
of isomeric saccharides that differ either by their composition of
monosaccharide units and/or the orientation of their glycosidic linkages.
We demonstrate the utility of this approach from single monosaccharides
up to isomeric tetrasaccharides differing only by the configuration
of a single glycosidic linkage. Furthermore, through hyphenation with
hydrophilic interaction liquid chromatography, we identify oligosaccharide
biomarkers in patient body fluid samples, demonstrating a generalized
and highly sensitive MS-based method for the identification of saccharides
found in complex sample matrices.