Abstract

European Journal of Mass Spectrometry
Volume 15 Issue 2, Pages 283–291 (2009)
doi: 10.1255/ejms.962

Unintended parametric ejection of ions from an ion cyclotron resonance trap by two-electrode axialization

Franklin Martinez, Alexander Herlert, Gerrit Marx, Lutz Schweikhard and Noelle Walsh
Institut für Physik, Ernst-Moritz-Arndt-Universität Greifswald, D-17487 Greifswald, Germany. E-mail: martinez@physik.uni-greifswald.de

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 2ν_z and ν_p = ν₊ – ν_– 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.

Keywords: ion cyclotron resonance, Penning trap, axialization, buffer-gas cooling, ion ejection

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