非对称双曲面线形离子阱的设计及性能研究

为提升离子阱质量分析器的分析性能，本文提出一种非对称双曲面线形离子阱结构，通过优化离子出射方向上x电极的单向拉伸距离Δr_a，引入合理的非对称射频电场，从而提高离子单向出射效率。利用SIMION和AXSIM模拟软件分析非对称双曲面线形离子阱的内部电场分布、离子运动轨迹及模拟质谱图。结果表明，在性能优化的对称双曲面线形离子阱结构的基础上，其中1个x电极单向拉伸Δr_a=0.8 mm时，通过优化AC频率和扫描速率等参数，非对称双曲面线形离子阱的离子单向出射率可达90%以上，同时m/z 609离子的质量分辨率超过5 100。经优化几何结构后的非对称双曲面线形离子阱可在保证高质量分辨率的情况下，大幅提高离子检测效率，这在小型化质谱仪的开发中具有显著的优势。

Design and Performance Evaluation of Asymmetric Hyperboloid Linear Ion Trap

Hyperbolic electrode linear ion trap is a good choice as the mass analyzer of miniaturized ion trap mass spectrometer for the reason that it has a compact size and excellent performance. However, ions are ejected from both opposite directions along the x-axis for existing hyperbolic electrode linear ion trap, which means that the ion detection efficiency could not be higher than 50% if only one ion detector is employed in the miniaturized ion trap mass spectrometer. This symmetrical structure significantly influences the analysis performance of hyperbolic electrode linear ion trap and limits the application at miniaturized ion trap mass spectrometer. Therefore, in order to further improve the ion detection efficiency of the ion trap, an asymmetric hyperboloid linear ion trap structure was proposed. By optimizing the unidirectional stretching distance Δr_a of the x-axis electrode in the direction of ion ejection after the optimization to the stretching distances Δr_x of both x-axis electrodes, a reasonable asymmetric radio frequency electric field was introduced for improving ion unidirectional ejection efficiency. The samples used in the simulation experiments were ions with m/z 609, 610 and 611. The internal electric field distribution, ion motion trajectory and simulated mass spectra peak of the asymmetric hyperboloid linear ion trap for different electrode structures were analyzed by simulation software SIMION and AXSIM. Then the ion unidirectional ejection efficiency and mass resolution were calculated, and the data were drawn as line charts. The simulation results showed that on the basis of the optimized symmetrical hyperboloid ion trap structure, whose x-axis electrodes were both stretched by Δr_x=0.9 mm, an ion unidirectional ejection efficiency of over 90% and a mass resolution over 5 100 for m/z 610 were achieved by optimizing the parameters such as AC frequency and scanning rate, when one of the x-axis electrodes was unidirectionally stretched by Δr_a=0.8 mm. In addition, under the condition of ions with large m/z 1 890, a mass resolution up to 10 590 and an ion unidirectional ejection efficiency of 93.3% were achieved when Δr_a=0.7 mm. It proved that the asymmetric hyperboloid linear ion trap with the optimized geometric structure could greatly improve the ion detection efficiency with only one ion detector under the guarantee of high mass resolution, which had a significant advantage for developing miniaturized ion trap mass spectrometer in the future. On the whole, the research could provide a theoretical foundation for further investigations, but there were still some problems to be solved, such as the actual processing, assembly and experiment.