Xuan Xiangchun
Department of Mechanical Engineering, Clemson University, Clemson, SC, USA.
Electrophoresis. 2008 Sep;29(18):3737-43. doi: 10.1002/elps.200800098.
Ionic species with a constant charge-to-size ratio (i.e. electrophoretic mobility) cannot be separated in electroosmotic or pressure-driven flow along microscale channels. In nanoscale channels, however, the enormous electric fields inside electrical double layers cause transverse ion distributions yielding charge-dependent mean ion speeds in the flow. Those ions with a constant charge-to-size ratio can thus be separated solely by charge (or equivalently, size) in nanofluidics. Here we develop an analytical model to optimize and compare the separation of such ions in nanochannel chromatography and nanochannel electrophoresis in terms of selectivity, plate height and resolution. Both planar and cylindrical geometries are considered. It is found that in nanoscale channels chromatography yields a larger selectivity and a larger minimum reduced plate height than electrophoresis does. The maximum resolution is, however, comparable between these two nanofluidic approaches, where the optimal channel half-height or tube radius is within the range of 1-10 times the Debye length. Our results also suggest that cations can be better separated in nanofluidics than can anions.
在沿微尺度通道的电渗流或压力驱动流中，具有恒定电荷与尺寸比（即电泳迁移率）的离子物种无法被分离。然而，在纳米尺度通道中，双电层内部的巨大电场会导致横向离子分布，从而在流动中产生与电荷相关的平均离子速度。因此，那些具有恒定电荷与尺寸比的离子在纳米流体学中仅通过电荷（或等效地，尺寸）就可以被分离。在这里，我们开发了一个分析模型，以在选择性、板高和分辨率方面优化和比较此类离子在纳米通道色谱和纳米通道电泳中的分离情况。同时考虑了平面和圆柱形几何形状。研究发现，在纳米尺度通道中，色谱法比电泳法具有更大的选择性和更小的最小折合板高。然而，这两种纳米流体方法的最大分辨率相当，其中最佳通道半高或管半径在德拜长度的1 - 10倍范围内。我们的结果还表明，阳离子在纳米流体学中比阴离子能得到更好的分离。
