Resonance methods in quadrupole ion traps

Abstract

The quadrupole ion trap is widely used in the chemical physics community for making measurements on dynamical systems, both intramolecular (e.g. ion fragmentation reactions) and intermolecular (e.g. ion/molecule reactions). In this review, we discuss linear and nonlinear resonances in quadrupole ion traps, an understanding of which is critical for operation of these devices and interpretation of the data which they provide. The effect of quadrupole field nonlinearity is addressed, with important implications for promoting fragmentation and achieving unique methods of mass scanning. Methods that depend on ion resonances (i.e. matching an external perturbation with an ion's induced frequency of motion) are discussed, including ion isolation, ion activation, and ion ejection.

Nonlinear resonances in linear segmented Paul trap of short central segment

“…The resonances observed can find application in mass selection of ions trapped with application of electron gun, where some undesirable ions could be produced: If any single‐species ensemble of ions is required, the phenomenon can be applied for purification of ion sets. Another possible application is mass spectrometry for analysis of composition of multispecies ion ensembles at various experimental conditions, allowing, for example, for electron‐impact ionization cross section determination …”

“…Another possible application is mass spectrometry for analysis of composition of multispecies ion ensembles 10,16,17 at various experimental conditions, allowing, for example, for electron-impact ionization cross section determination. 18…”

“…If the trap's potential is not harmonic (which is true for real, not idealized devices), then some effects of nonlinear resonances can be observed, where ions rapidly gain kinetic energy from the trap's electric field. Such effects were noticed at early stages of development of ion trapping techniques and described in detail in numerous works on 3‐dimensional traps and only in few works on linear traps …”

“…If the trap's potential is not harmonic (which is true for real, not idealized devices), then some effects of nonlinear resonances can be observed, where ions rapidly gain kinetic energy from the trap's electric field. Such effects were noticed at early stages of development of ion trapping techniques 3 and described in detail in numerous works on 3-dimensional traps [4][5][6][7][8][9][10][11] and only in few works on linear traps. 12,13 In spite of broad knowledge on the effects, such resonances have not been described for linear, segmented traps using short central segments of the electrodes.…”

Free radical‐initiated peptide sequencing (FRIPS)‐based cross‐linkers for improved peptide and protein structure analysis

“…The low‐energy tandem MS approach is most often used for peptide and protein sequencing, typically requiring multiple collisions to reach the excitation levels that allow the dissociation of covalent bonds to take place. The stepwise excitation process via a sequential uptake of small‐energy quanta by multiple low‐energy collisions with light and inert helium gas atoms is very slow (>10 −2 s), but is established in both spherical and linear quadrupole ion traps, in which helium is present at substantial pressures (P He ≈ 0.1 Pa) . Low‐energy CID is among the slow‐heating methods for ion activation .…”