Predicting ion mobility as a function of the electric field for small ions in light gases
Predicting ion mobility as a function of the electric field for small ions in light gases
复制标题
预测轻气体中小离子的离子迁移率与电场的关系
DOI：
10.1016/j.aca.2021.339019
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发表时间：
2021
影响因子：
6.2
通讯作者：
Larriba-Andaluz, Carlos
中科院分区：
文献类型：
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作者：
Gandhi, Viraj D.;Larriba-Andaluz, Carlos
高分辨率迁移率设备，例如场不对称波形离子迁移谱仪（FAIMS）和差分迁移谱仪（DMS），使用强电场与气体浓度比E/N来分离气相中的离子。虽然非常成功，但他们的经验结果显示了迁移率K和E/N之间的非线性，离子依赖关系，难以表征。不幸的是，单温度理论Mason-Schamp方程，这是最广泛使用的离子迁移率方程，不能捕捉到这种行为。当使用双温理论时，可以证明，通过将场的增加等同于离子温度的增加，可以在数值上非常接近地遵循K-E/N行为。这是尝试在这里的小离子在氦气环境中显示良好的协议在整个字段范围。为了改善数值表征，可以优化Lennard-Jones（LJ）势。这是试图为碳，氢，氧和氮在不同程度的理论，直到第四近似，这是假设是准确的。LJ的优化提高了精度，平均误差约为3%。一组恒定的LJ势适用于整个E/N范围和几个分子，这一事实也表明，在He的计算中可以避免非弹性碰撞。研究了特殊的K-E/N驼峰行为，并表明迁移率随E/N的增加或减少来自相对动能和相互作用势之间的竞争。
High resolution mobility devices such as Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) and Differential Mobility spectrometers (DMS) use strong electric fields to gas concentration ratios, E/N, to separate ions in the gas phase. While extremely successful, their empirical results show a non-linear, ion-dependent relation between mobility K and E/N that is difficult to characterize. The one-temperature theory Mason-Schamp equation, which is the most widely used ion mobility equation, unfortunately, cannot capture this behavior. When the two-temperature theory is used, it can be shown that the K− E/N behavior can be followed quite closely numerically by equating the effect of increasing the field to an increase in the ion temperature. This is attempted here for small ions in a Helium gas environment showing good agreement over the whole field range. To improve the numerical characterization, the Lennard-Jones (LJ) potentials may be optimized. This is attempted for Carbon, Hydrogen, Oxygen and Nitrogen at different degrees of theory up to the fourth approximation, which is assumed to be exact. The optimization of LJ improves the accuracy yielding errors of about 3% on average. The fact that a constant set of LJ potentials work for the whole range of E/N and for several molecules, also suggests that inelastic collisions can be circumvented in calculations for He. The peculiar K− E/N hump behaviors are studied, and whether mobility increases or decreases with E/N is shown to derive from a competition between relative kinetic energy and the interaction potentials.