Ion collision crosssection measurements in quadrupole ion traps using a time–frequency analysis method

Abstract

In this study, a method for measuring ion collision crosssections (CCSs) was proposed through time-frequency analysis of ion trajectories in quadrupole ion traps. A linear ion trap with added high-order electric fields was designed and simulated. With the presence of high-order electric fields and ion-neutral collisions, ion secular motion frequency within the quadrupole ion trap will be a function of ion motion amplitude, thus a function of time and ion CCS. A direct relationship was then established between ion CCS and ion motion frequency with respect to time, which could be obtained through time-frequency analysis of ion trajectories (or ion motion induced image currents). To confirm the proposed theory, realistic ion trajectory simulations were performed, where the CCSs of bradykinin, angiotensin I and II, and ubiquitin ions were calculated from simulated ion trajectories. As an example, differentiation of isomeric ubiquitin ions was also demonstrated in the simulations.

Ion collision cross section measurements in Fourier transform-based mass analyzers

“…Besides FT-ICR, the Fourier transform technology could also be applied to quadrupole ion traps, and ion CCS measure- ments could also be performed in quadrupole ion traps. 44,45 In a quadrupole ion trap, ion kinetic energies after excitation are very different from those in a modern FT-ICR cell. First, ion kinetic energies are much lower in a quadrupole ion trap, typically on the level of tens of electron volts.…”

Accurate modelling of small-scale linear ion trap operating mode using He buffer gas to improve sensitivity and resolution for in-the-field mass spectrometry

“…Although He buffer gas use could be disadvantageous for device portability, it was chosen instead of residual ambient air because of the improved performance that may be obtained. Many recent simulation papers neglect the influence of the RF trapping field by using the pseudo-potential approximation and consider that collisions induce a damping effect upon ion trajectories 15,16 . However, Schwarz emphasised in 2008 the necessity for a microscopic description of the RF heating and to take into account the statistical nature of the collisions 17 .…”

Collision cross section measurements for biomolecules within a high-resolution FT-ICR cell: theory

“…In this case, the hard-sphere collision model is more accurate. 18 Although the Langevin and the hard-sphere collision models have been successfully applied in the characterization of ion damping motions within ICR cells, as well as in quadrupole ion traps, 19,20 there are limitations in describing high energy ion-neutral collisions, 21,22 especially in modern high-resolution FT-ICR systems. [23][24][25] By proposing that ion-neutral collisions scatter ions out of a coherent packet, Yang et al realized the CCS measurement of crown ether ions in a 4.7 T FT-ICR instrument.…”