Discrimination of cyclic and linear oligosaccharides by tandem mass spectrometry using collision-induced dissociation (CID), pulsed-Q-dissociation (PQD) and the higher-energy C-trap dissociation modes

RATIONALE Carbohydrates have essential functions in living organisms and cells, but, due to the presence of numerous linkage combinations, substituent sites and possible conformations, they are the class of biomolecules which exhibits the huge structural diversity found in nature. Thereby, due to such diversity and poor ionization, their structural deciphering by mass spectrometry is still a very challenging task. METHODS Here, we studied a series of linear and cyclic neutral oligosaccharides using electrospray with collision-induced dissociation (CID), pulsed-Q-dissociation (PQD) and the higher-energy C-trap dissociation (HCD) feature of a linear ion trap Orbitrap hybrid mass spectrometer (LTQ-Orbitrap). The collision energy necessary to obtain 50% fragmentation (CE50 values) in CID, PQD and HCD was used to correlate both size and structures. RESULTS The default settings for activation time and/or activation Q are the most appropriate, except for HCD, where 100 ms instead of 30 ms gave more intense fragment ions. PQD exhibits a 28-fold lower sensitivity than CID. HCD provides signals closer or slightly superior by 1.5-fold than PQD, and offers a more balanced ion distribution through the spectrum. Furthermore, HCD offers the possibility to make fine adjustments of the energy via the eV scale to further increase the yield of low-mass fragments. CONCLUSIONS The complementarity of CID, PQD and HCD was clearly demonstrated by obtaining structural information on hexa-, hepta- and octasaccharides. Together, these results clearly indicate the usefulness of the CID/HCD pair for further structural deciphering, and analysis of more complex structures such as multi-antennary carbohydrates or glycoconjuguates alone or in mixture. Copyright (c) 2012 John Wiley & Sons, Ltd.