Fundamentals of Trapped Ion Mobility Spectrometry Part II: Fluid Dynamics
Fundamentals of Trapped Ion Mobility Spectrometry Part II: Fluid Dynamics
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DOI：
10.1007/s13361-015-1310-z
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发表时间：
2016-04-01
影响因子：
3.2
通讯作者：
Park, Melvin A.
中科院分区：
文献类型：
--
作者：
Silveira, Joshua A.;Michelmann, Karsten;Park, Melvin A.
俘获离子迁移率光谱(TIMS)是一种新的高分辨率(R高达300)的分离技术，它利用电场使静止的离子与移动的气体保持不变。最近，建立了TIMS的分析模型，并在一定程度上进行了实验验证。该模型的一个核心但尚未完全探索的组成部分涉及到工作中的流体动力学。本研究通过模拟和离子迁移率实验表征了TIMS中的流体动力学。结果表明，分析器内存在亚音速层流，在离子洗脱位置测得的气速随压力变化在120~170m/S之间。其中一个关键的哲学问题是：如何在一个气体在膨胀、速度在变化的动态系统中测量迁移率？我们以前注意到，分析上有用的工作主要是在离子穿过分析仪中的电场梯度平台时完成的。在目前的工作中，我们证明了高原上气体速度随位置的变化被压力和温度的变化所平衡，最终导致了与位置无关的阻力。阻力和相关变量几乎是恒定的，这使得可以使用相对简单的方程来描述TIM的行为。然而，我们得到了一个更全面的模型，它解释了流动变量的空间相关性。实验分辨率的变化趋势与阻力的理论依赖关系非常一致，从而验证了TIMS理论的另一个主成分。
Trapped ion mobility spectrometry (TIMS) is a new high resolution (R up to similar to 300) separation technique that utilizes an electric field to hold ions stationary against a moving gas. Recently, an analytical model for TIMS was derived and, in part, experimentally verified. A central, but not yet fully explored, component of the model involves the fluid dynamics at work. The present study characterizes the fluid dynamics in TIMS using simulations and ion mobility experiments. Results indicate that subsonic laminar flow develops in the analyzer, with pressure-dependent gas velocities between similar to 120 and 170 m/s measured at the position of ion elution. One of the key philosophical questions addressed is: how can mobility be measured in a dynamic system wherein the gas is expanding and its velocity is changing? We noted previously that the analytically useful work is primarily done on ions as they traverse the electric field gradient plateau in the analyzer. In the present work, we show that the position-dependent change in gas velocity on the plateau is balanced by a change in pressure and temperature, ultimately resulting in near position-independent drag force. That the drag force, and related variables, are nearly constant allows for the use of relatively simple equations to describe TIMS behavior. Nonetheless, we derive a more comprehensive model, which accounts for the spatial dependence of the flow variables. Experimental resolving power trends were found to be in close agreement with the theoretical dependence of the drag force, thus validating another principal component of TIMS theory.