Comprehensive Theory of the Deans' Switch As a Variable Flow Splitter: Fluid Mechanics, Mass Balance, and System Behavior
Comprehensive Theory of the Deans' Switch As a Variable Flow Splitter: Fluid Mechanics, Mass Balance, and System Behavior
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DOI：
10.1021/ac401419j
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发表时间：
2013-10-01
影响因子：
7.4
通讯作者：
Lammers, Peter Schulze
中科院分区：
文献类型：
--
作者：
Boeker, Peter;Leppert, Jan;Lammers, Peter Schulze
Deans开关是一种基于控制载气流量的流出物开关装置，而不是分析流路中的机械阀。该技术提供了高惰性和无磨损操作。最近，新的单片微流体装置已经变得可用。在这些装置中，整个流动系统被集成到具有低热质量和密封连接的小金属装置中。与基于机械阀的系统相比，流量控制系统更难以计算。通常，Deans开关用于通过两个辅助流将一个入口切换到两个出口中的一个。然而，Deans开关也可用于将具有特定分流比的GC流出物输送到两个出口。由于流动阻力的不对称性，入口流到两个出口的分流比的计算具有挑战性。如果其中一个出口是真空装置，例如质谱仪，而另一个出口是大气检测器，例如火焰离子化检测器（FID）或嗅觉（嗅探）端口，则情况尤其如此。气相色谱中的毛细管流动是用圆管中层流、等温、可压缩流动的Hagen-Poiffille方程计算的。新的微流控器件中的流动阻力必须用矩形截面微通道的相应方程来计算。Hagen-Poiffille方程低估了真空出口的流量。本文提出了一个修正的稀薄流理论方程。基于迪安开关的色谱系统的压力和流量的计算通过质量平衡的解来完成。一个具体的挑战是考虑Deans开关的两个辅助气体管线之间的防扩散电阻器。提出了包括该限制器在内的Deans开关计算的完整解决方案。验证测量的结果与所发展的理论是一致的。基于电子表格的流量计算器是支持信息的一部分。
The Deans' switch is an effluent switching device based on controlling flows of carrier gas instead of mechanical valves in the analytical flow path. This technique offers high inertness and a wear-free operation. Recently new monolithic microfluidic devices have become available. In these devices the whole flow system is integrated into a small metal device with low thermal mass and leak-tight connections. In contrast to a mechanical valve-based system, a flow-controlled system is more difficult to calculate. Usually the Deans' switch is used to switch one inlet to one of two outlets, by means of two auxiliary flows. However, the Deans' switch can also be used to deliver the GC effluent with a specific split ratio to both outlets. The calculation of the split ratio of the inlet flow to the two outlets is challenging because of the asymmetries of the flow resistances. This is especially the case, if one of the outlets is a vacuum device, such as a mass spectrometer, and the other an atmospheric detector, e.g. a flame ionization detector (FID) or an olfactory (sniffing) port. The capillary flows in gas chromatography are calculated with the Hagen-Poiseuille equation of the laminar, isothermal and compressible flow in circular tubes. The flow resistances in the new microfluidic devices have to be calculated with the corresponding equation for rectangular cross-section microchannels. The Hagen-Poiseuille equation underestimates the flow to a vacuum outlet. A corrected equation originating from the theory of rarefied flows is presented. The calculation of pressures and flows of a Deans' switch based chromatographic system is done by the solution of mass balances. A specific challenge is the consideration of the antidiffusion resistor between the two auxiliary gas lines of the Deans' switch. A full solution for the calculation of the Deans' switch including this restrictor is presented. Results from validation measurements are in good accordance with the developed theories. A spreadsheet-based flow calculator is part of the Supporting Information.