Unintended Parametric Ejection of Ions from an Ion Cyclotron Resonance Trap by Two-Electrode Axialization

Azimuthal quadrupolar excitation is a commonly used technique in the field of ion cyclotron resonance mass spectrometry, in particular in combination with buffer-gas collisions to achieve axialization of the stored ions. If the quadrupolar excitation is applied with only one phase to a set of two opposing ring segments (rather than the “regular” method where two sets of electrodes are addressed with opposite polarities), parametric resonance effects at the frequencies 2μ z and μp = μ+ – μ– can lead to unintended ejection of ions from the trap. These parametric resonances have been revisited both theoretically and experimentally: multipole components of different azimuthal excitation schemes are derived by a simple vector representation of the excitation signal applied to the ring segments. Thus, parametric contributions can be easily identified, as demonstrated for the two-electrode and the four-electrode quadrupolar excitation schemes as well as further examples. In addition, the effect of the single-phase two-electrode quadrupolar excitation is demonstrated for storage and axialization of cluster ions.

Quadrupole Mass Filter Transmission in Island a of the First Stability Region with Quadrupolar Excitation

With quadrupolar excitation of ions by a small auxiliary RF field, the first stability region of the quadrupole mass filter splits into islands of stability. This study is of the first upper island, “A”. We calculate the location of this island for different values of the excitation parameter, q‘. Ion trajectory calculations are used to study the influence of the input fringing fields and the separation time. The Runge-Kutta–Nustrom–Dormand-Prince (RK–N–DP) method of order 6(7) is used for integration of the equations of ion motion. It is found that a weak auxiliary RF signal improves the peak shape for quadrupole mass filters that have weak field distortions.