Collision-Induced Dissociation (CID)
CID fragments are usually produced in collision cells filled with an inert gas, and because fragmentation is isolated from ion production, it can be controlled by application of varying voltages on the collision cell. In positive ion mode, low-energy collisions with glycans produce mainly glycosidic cleavages and low amounts of cross-ring cleavages, mainly of the A type. Higher-energy collisions of the type produced with TOF/TOF instruments or magnetic sector instruments fitted with an orthogonal TOF analyzer [245, 265] produce spectra with a larger proportion of X-type cleavage ions . Glycopeptides tend to produce most fragment ions from the glycan moiety because of the weaker bonds in this part of the molecule [267-269]. Kolli and Dodds  have used energy-resolved spectra to show with an N-linked glycopeptide from Erythrina cristagalli lectin (ECL) (17 amino acids) that, at a collision cell voltage of 17.5 V, the fragmentation spectrum of the triply protonated ion contained only glycosidic cleavage ions, whereas at 37.5 V mainly b- and y-type peptide fragments were observed. By switching between the two energies, a composite spectrum was obtained. Similar results were obtained with the Man5GlcNAc2- SRNLTK glycopeptide from ribonuclease B. The presence of glycans on the peptides is revealed by the production of oxonium ions such as those from hexose (m/z 163), HexNAc (m/z 204), Neu5Ac (m/z 292), and HexHexNAc (m/z 366).