The
isomeric heterogeneity of glycans poses a great challenge for
their analysis. While combining ion mobility spectrometry (IMS) with
tandem mass spectrometry is a powerful means for identifying and characterizing
glycans, it has difficulty distinguishing the subtlest differences
between isomers. Cryogenic infrared spectroscopy provides an additional
dimension for glycan identification that is extremely sensitive to
their structure. Our approach to glycan analysis combines ultrahigh-resolution
IMS-IMS using structures for lossless ion manipulation (SLIM) with
cryogenic infrared spectroscopy. We present here the design of a SLIM
board containing a series of on-board traps in which we perform collision-induced
dissociation (CID) at pressures in the millibar range. We characterize
the on-board CID process by comparing the fragments generated from
a pentapeptide to those obtained on a commercial tandem mass spectrometer.
We then apply our new technique to study the mobility and vibrational
spectra of CID fragments from two human milk oligosaccharides. Comparison
of both the fragment drift times and IR spectra with those of suitable
reference compounds allows us to identify their specific isomeric
form, including the anomericity of the glycosidic linkage, demonstrating
the power of this tool for glycan analysis.
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