Calculation of the composition of sample zones in capillary zone electrophoresis I. Mathematical model

Abstract

A mathematical model was set up for the calculation of all parameters in sample zones in capillary zone electrophoresis. In this model, sample peaks are divided into small segments with varying sample component concentrations and all parameters of a segment can be calculated from the parameters of the preceding segment with a steady-state model, based on the mass balances of the co- and counter ions, the electroneutrality equation and the modified Ohm's law. In this way, non-steady-state electrophoretic processes can be estimated by a repeated application of a steady-state model. Although in this model only the electrodispersive effect is considered and other peak broadening effects, such as diffusion, are neglected, this model is very useful to obtain an insight into the electrophoretic separation procedure and to calculate how parameters change in a sample zone. Calculations with this model show that linear relationships are obtained between the concentration of the sample component and other parameters, such as the pH, concentrations of co- and counter ions, electric field strength and specific resistance in the sample zone, if the sample concentration is not extremely high. With this model electropherograms can be simulated on a spatial basis whereby all possible detector signals can be calculated. The combined effect of a change in pH, resulting in a change in effective mobility for weak acids and bases, and a change in the electric field strength leads to a change in the apparent mobility of the different segments of the sample peaks. For sample ions, both anions and cations, with a mobility higher than that of the co-ions of the background electrolyte a diffuse front side results from the calculations whereas tailing peaks are obtained for sample components with low mobilities.