Simulation of double resonant excitation of ions in an asymmetric linear ion trap mass analyzer

Rationale: Improving the analytical performance of linear ion traps (LITs) is crucial for the advancement of high-performance LIT mass spectrometers. In this study, a double resonant excitation method was employed in an asymmetric LIT to achieve high ion unidirectional ejection efficiency and enhanced mass resolution. Methods: The asymmetric trapping field was generated by stretching one x electrode with a distance alpha. The double resonant excitation was achieved by applying an alternating voltage out of phase and a supplementary alternating voltage in phase to the x and y electrode pairs of the LIT, respectively. Numerical simulations of ion trajectories were performed to validate the effectiveness of this method. Results: The mass resolution of the asymmetric LIT with double resonant excitation could be improved to similar to 3800, which was over two times compared to that with only dipolar resonant excitation, while both reached similar to 90% in ion unidirectional ejection efficiency. Conclusions: By employing the double resonant excitation method, the mass resolution could be improved significantly in the asymmetric LIT, while maintaining a considerably high ion unidirectional ejection efficiency. This method might provide a general solution for enhancing ion detection efficiency and mass resolution of LIT mass spectrometers.