The Gene and Linda Voiland School of Chemical Engineering and Bioengineering, Washington State University, Pullman, WA 99164-2710, USA.
J Sep Sci. 2013 Jun;36(12):1986-95. doi: 10.1002/jssc.201300066. Epub 2013 May 13.
The purpose of applying a countercurrent flow to isotachophoretic migration is to increase the effective separation channel length during ITP. However, severe dispersion induced by applying a counterflow can be detrimental to ITP. This paper uses numerical simulations in a 2D axisymmetric domain to investigate the dispersion caused by a parabolic counterflow in open-capillary ITP. Counterflow in these simulations was generated by applying a back pressure to stop the isotachophoretic stack, i.e., forming stationary ITP zones. It is found that dispersion is strongly related to analyte molecular diffusivity: R-phycoerythrin, due to its small diffusivity, showed ~20-fold increase in zone width in stationary counterflow ITP, compared to ITP in the absence of counterflow, while fluorescein only had ~10% increase in zone width under similar operating conditions. Applying the Taylor-Aris dispersion formula in counterflow ITP simulations provided only a rough estimate of the dispersion, e.g., overestimation of analyte zone widths. Experiments on counterflow ITP were conducted in a silica capillary that was covalently and dynamically coated to exclude electroosmosis effect. The counterflow was generated by adjusting the relative height of the fluids in the two reservoirs at the capillary ends. Good qualitative agreement between simulations and experiments was found.
应用逆流流动进行等速电泳迁移的目的是增加 ITP 期间的有效分离通道长度。然而，应用逆流会引起严重的弥散，这对 ITP 是不利的。本文使用二维轴对称域中的数值模拟来研究在开管等速电泳中抛物线逆流引起的弥散。在这些模拟中，通过施加背压来停止等速电泳堆积，即形成固定的 ITP 区，从而产生逆流。结果发现，弥散强烈地与分析物分子扩散系数有关：R-藻红蛋白由于其较小的扩散系数，在固定逆流等速电泳中，与没有逆流的等速电泳相比，区宽增加了约 20 倍，而在类似的操作条件下，荧光素的区宽仅增加了约 10%。在逆流等速电泳模拟中应用泰勒-阿里斯弥散公式仅提供了弥散的大致估计，例如，对分析物区宽的高估。在共价和动态涂层以排除电渗流效应的二氧化硅毛细管中进行了逆流等速电泳实验。通过调整毛细管两端两个储液器中流体的相对高度来产生逆流。模拟和实验之间存在良好的定性一致性。
