Mannose7 Glycan Isomer Characterization by IMS-MS/MS Analysis

The isomers of the Man₇GlcNAc₂ glycan obtained from bovine ribonuclease B have been characterized by ion mobility spectrometry-tandem mass spectrometry (IMS-MS/MS). In these experiments, [Man7 + 2Na]²⁺ precursors having different mobilities are selected by ion mobility spectrometry and analyzed by MS/MS techniques in an ion trap. The fragmentation spectra obtained for various precursor ions are specific, suggesting the isolation or enrichment of different glycan isomers. One fragment ion with a mass-to-charge ratio (m/z) of 903.8 is found to correspond to the loss of an internal mannose residue of a specific isomer. Extracted fragment ion drift time distributions (XFIDTDs) yield distinctive precursor ion drift time profiles indicating the existence of four separate isomers as proposed previously.