Beckers J, Bocek P
Eindhoven University of Technology, Laboratory of Instrumental Analysis, Netherlands.
Electrophoresis. 1999 Mar;20(3):518-24. doi: 10.1002/(SICI)1522-2683(19990301)20:3<518::AID-ELPS518>3.0.CO;2-F.
Non-steady-state electrophoretic processes can be estimated by a repeated application of a steady-state model based on the electroneutrality equation, the modified version of Ohm's law, and the mass balances of the co- and counterions. With such a mathematical model, all parameters in sample zones in capillary zone electrophoresis (CZE) can be calculated. The relationships between the calculated parameters for sample zones in CZE, such as the pH, concentrations of co- and counterions, and the ratio E1m1/E2m2 versus the mobilities of both anionic and cationic analytes can be visualized in a SystChart, a set of eight panels, for a given background electrolyte (BGE). All properties of a zone, such as the fronting/tailing character and the question of peaks/dips can be read from such a SystChart. Applying n coions, n-1 discontinuities are present in such a SystChart, indicating the presence of system peaks applying that BGE. For BGEs with one coion, no system peaks (discontinuities) exist at moderate pH values. SystCharts calculated for BGEs with a low pH do show discontinuities, however, which indicates that system peaks are present in electropherograms applying BGEs at low pH. Experimentally, it is shown that system peaks are indeed present in electropherograms applying BGEs with one coion at low pH and the mobilities of the system peaks generally increase with decreasing pH. Hydrogen ions seem to act as a second coionic species. Of course, these system peaks are only visible in the UV signal if the BGE has UV-absorbing properties.
非稳态电泳过程可以通过基于电中性方程、修正版欧姆定律以及共离子和反离子质量平衡的稳态模型的重复应用来估计。利用这样的数学模型，可以计算毛细管区带电泳（CZE）中样品区的所有参数。对于给定的背景电解质（BGE），CZE中样品区的计算参数之间的关系，如pH值、共离子和反离子的浓度以及E1m1/E2m2与阴离子和阳离子分析物迁移率的比值，可以在一个SystChart（一组八个面板）中直观呈现。一个区的所有特性，如前沿/拖尾特征以及峰/谷问题，都可以从这样的SystChart中读取。应用n种共离子时，在这样的SystChart中会出现n - 1个不连续点，表明使用该BGE时存在系统峰。对于含有一种共离子的BGE，在中等pH值下不存在系统峰（不连续点）。然而，为低pH值的BGE计算的SystChart确实显示出不连续点，这表明在使用低pH值BGE的电泳图中存在系统峰。实验表明，在使用含有一种共离子的低pH值BGE的电泳图中确实存在系统峰，并且系统峰的迁移率通常随着pH值的降低而增加。氢离子似乎充当了第二种共离子物种。当然，只有当BGE具有紫外吸收特性时，这些系统峰才会在紫外信号中可见。
