Wang Wei, Bajic Steve, John Benzi, Emerson David R
STFC, Daresbury Laboratory, Warrington, Cheshire WA4 4AD, U.K.
Waters Corporation, Altrincham Rd, Wilmslow, Cheshire SK9 4AX, U.K.
J Am Soc Mass Spectrom. 2020 Apr 1;31(4):840-855. doi: 10.1021/jasms.9b00103. Epub 2020 Mar 5.
Understanding ion transport mechanisms in the flow expansion section of the first vacuum region of a mass spectrometer (MS) with an atmospheric pressure ionization source is essential for optimizing the MS sampling interface design. In this study, numerical simulations of three types of ions in two different MS interface designs have been carried out. In contrast to previously reported numerical studies, nonequilibrium gas dynamics due to rarefied gas effects has been considered in modeling the flow expansion and a realistic space charge effect has been considered in a continuous ion injection mode. Numerical simulations reveal that a flat plate interface has a higher peak buffer gas velocity but a narrower zone of silence compared to the conical interface. Shock wave structures are clearly captured, and the Knudsen number distribution is displayed. Simulation results show that in the axial direction the buffer gas effect is much stronger than the electric force effect in the current configuration. The conical interface leads to both a strong ion acceleration in the zone of silence and a strong ion deceleration downstream. In the radial direction, both the electric force and buffer gas drag force play an important role. The conical interface introduces a relatively stronger ion focusing effect from the radial buffer gas effect and a stronger ion dispersion from the radial electric force than the flat plate interface. The net effect for the current configuration is an increase in ion losses for the conical interface. Nanoelectrospray ionization experiments were carried out to validate the ion transmission efficiency.
了解具有大气压电离源的质谱仪（MS）第一真空区域流动扩展部分中的离子传输机制对于优化MS采样接口设计至关重要。在本研究中，对两种不同MS接口设计中的三种离子进行了数值模拟。与先前报道的数值研究不同，在对流动扩展进行建模时考虑了稀薄气体效应引起的非平衡气体动力学，并且在连续离子注入模式下考虑了实际的空间电荷效应。数值模拟表明，与锥形接口相比，平板接口具有更高的峰值缓冲气体速度，但沉默区更窄。清晰地捕捉到了冲击波结构，并显示了克努森数分布。模拟结果表明，在当前配置中，轴向缓冲气体效应比电力效应要强得多。锥形接口在沉默区内导致强烈的离子加速，在下游导致强烈的离子减速。在径向方向上，电力和缓冲气体拖曳力都起着重要作用。与平板接口相比，锥形接口从径向缓冲气体效应引入了相对更强的离子聚焦效应，从径向电力引入了更强的离子分散。当前配置的净效应是锥形接口的离子损失增加。进行了纳米电喷雾电离实验以验证离子传输效率。
