Extending the mass range of the quadrupole ion trap using axial modulation

Abstract

AbstractSecondary‐ion mass spectrometry, using Cs+ ion bombardment of solid and liquid matrices, has been implemented on a quadrupole ion trap. Tetraalkylammonium cations and protonated peptides, generated in an external source using a pulsed primary‐ion beam, are injected into the ion trap where they are decelerated and trapped in the course of collisions with the helium bath gas. The contents of the trap are then examined by recording a mass spectrum using the mass‐selective instability scan. To improve performance in the examination of these trapped ions, the technique of axial modulation is used to cause resonance ejection of ions from the trap during the mass‐analysis step. The supplementary AC voltage applied to the end‐caps causes resonant ejection of ions at qz values below those which correspond to the normal stability limit. This is demonstrated to increase the mass limit of a commercial ion trap from 650 Da to approximately 1300 Da with no loss in resolution or sensitivity, and to more than 20 000 Da at reduced sensitivity.