Research of Unidirectional Ion Ejection in Triangular-Electrodes Ion Trap with Asymmetric Geometry

The triangular-electrode linear ion trap (TeLIT) has simple structure and good performance. For existed TeLIT, ions were ejected from both sides along the x axis, which meant that the ion detection efficiency would not be higher than 50% if only one ion detector was used, as it usually did. To solve this problem, two ion detectors were used in commercialized LIT mass spectrometer. However, this configuration requires relatively large vacuum chamber and higher cost, which is undesirable for developing miniaturized mass spectrometer. To improve ion detection efficiency without additional ion detector, a new type of TeLIT with asymmetric geometry was constructed. The two triangular electrodes on the ion ejection direction (x axis) were built with different angles, which would introduce asymmetric electric fields in TeLIT and cause unidirectional ion ejection. The relationship between electrode angle difference (Δα) and internal electric field distributions was calculated by numerical simulation method. At the same time, the ion trajectories and simulated mass spectra were simulated by software SIMION and AXSIM, and then mass resolution and ion unidirectional efficiency were calculated . Ions (m/z 609, 610 and 611) were used in the simulation, and the simulation results showed that, for m/z 610, a mass resolution of 2647 and an ion unidirectional ejection efficiency of over 95% were achieved in TeLIT with Δα of 15°. So unidirectional ion ejection could be realized without loss of mass resolution in an optimized TeLIT with asymmetric geometry, and it would significantly improve ion detection efficiency with only one ion detector, which made the asymmetric TeLIT pretty suitable for developing miniaturized mass spectrometer. Although only the performance of asymmetric TeLIT by simulation was investigated in this study, this simulation results would be helpful and instructional for further experiment and study.