非对称三角形电极离子阱的单向出射性能模拟研究

三角形电极离子阱（triangular-electrode linear ion trap, TeLIT）是一种新型结构的线性离子阱，具有简单的电极结构和良好的分析性能。为进一步提高TeLIT的离子探测效率，本实验将离子出射方向的2个电极设置为不同角度，建立非对称结构的TeLIT，通过引入非对称场实现离子单向出射。通过分析电极角度差与其内部电场分布的关系，并模拟离子运动轨迹，获得离子出射情况和模拟质谱峰。理论模拟结果显示：当离子出射方向三角电极的角度差Δα=15°时，在优化的AC频率条件下，三角形电极离子阱的m/z 610离子单向出射率可达95%以上，且质量分辨率达到2647。经优化几何参数后的非对称三角形电极离子阱可在几乎不损失分辨率的情况下实现离子单向出射，大幅提高了单检测器模式下TeLIT的离子探测效率和仪器的灵敏度，使其在小型化质谱仪的开发中具有显著优势。

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.