稳定图的测定与矩形离子阱质谱性能分析

从理论上讲, 离子阱质谱仪的性能是由阱内电场分布决定的,而电场分布又是由组成离子阱的电极几何结构和离子阱工作电压决定的. 对于矩形离子阱, 即使不考虑其几何结构的偏差, 其阱内的电场分布一般也很复杂. 在矩形离子阱内, 除四极电场外, 还包含多种成分的其他各种高阶场, 它们直接影响离子在阱内的运动轨迹和离子阱质谱的性能. 由于各种电场成分对离子阱内离子运动的影响非常复杂, 还很难从数学上给出精确的解析解, 使得目前从理论上还无法预测高阶场成分对质谱性能的影响. 本工作通过测定不同几何结构的矩形离子阱的稳定图, 从实验上比较了不同场半径, 即不同电场分布条件下的离子阱质谱性能的差别. 实验中, 通过改变离子阱的几何比例结构, 详细测定了不同结构的矩形离子阱的稳定图特征, 并与实验测得的质谱分析结果进行比较. 同时, 我们还详细介绍了矩形离子阱质谱的稳定图的测定方法, 并根据得到的不同情况下的稳定图结构分析了离子阱的质谱性能. 研究结果表明： 可以通过比较试验得到的稳定图结构来判断其离子阱质谱仪的性能如质量分辨能力等. 此外, 实验结果还发现： 对于y方向拉伸结构的矩形离子阱, 其实验绘制得到的是不完整的稳定图. 但根据稳定图边界的特点, 通过采用四极直流电压调制的方法, 可以对y方向拉伸结构的矩形离子阱的性能进行改善, 极大地提高了阱的质量分辨能力.

Stability diagram mapping and the performance of rectilinear ion trap mass spectrometry

The performance of the ion trap mass spectrometer depends on the electric field distribution in the trap, while the electric field distribution is determined by the ion trap electrode geometry and the voltage applied. For rectilinear ion trap （RIT）, the electric field distribution is complex even ignoring the geometry defection. There are many higher order fields besides the quadrupole field, which directly affect the ion trajectories inside the trap and the performance of ion trap mass spectrometry. It is very difficult to describe the ion motion and the property of RIT mathematically, so that it is impossible to predict the impact of the high order field components on the performance of a rectilinear ion trap. In this paper, the stability diagrams of RITs with different geometries were mapped and their performances were compared. In the experiment, we investigated the stability diagram of different RITs by changing the proportion of trap electrodes. Meanwhile, we also gave in detail the method of stability diagram mapping, and compared the property of the ion trap mass spectrometer according to the structure of the stability diagrams. The results show that the performance of RIT such as mass resolution can be estimated by simply comparing their stability diagram. In addition, the incomplete stability diagrams were obtained for y-direction stretched RITs. And the performance of y-direction stretched RITs could be improved remarkably by modulating the quadrupolar-DC voltages according to the characteristics of the boundaries of its stability diagram,