Investigation of bovine ubiquitin conformers separated by high-field asymmetric waveform ion mobility spectrometry: Cross section measurements using energy-loss experiments with a triple quadrupole mass spectrometer

High-field asymmetric waveform ion mobility spectrometry (FAIMS) was used t o separate gas-phase conformers of bovine ubiquitin produced by electrospra y ionization. These conformers were sampled by a triple quadrupole mass spe ctrometer where energy-loss experiments, following the work of Douglas and co-workers, were used to determine their cross sections. The measured cross sections for some conformers were readily altered by the voltages applied to the interface ion optics, therefore very gentle mass spectrometer interf ace conditions were required to preserve gas-phase conformers separated by FAIMS. Cross sections for 19 conformers (charge states +5 through +13) were measured. Two conformers for the +12 charge state, which were readily sepa rated in FAIMS, were found to have similar cross sections. Based on a metho d to calibrate the collision gas thickness, the cross sections measured usi ng the FAIMS/energy-loss method were compared with literature values determ ined using drift tube ion mobility spectrometry. The comparison illustrated that the conformers of bovine ubiquitin that were identified using drift t ube ion mobility spectrometry were also observed using the FAIMS device. (J Am Soc Mass Spectrom 2000, 11, 738-745) (C) 2000 American Society for Mass Spectrometry.