Relevance of the calculation of the diffusion coefficient in a capillary electrophoresis experiment

Abstract

This paper analyzes the role of the diffusion coefficient in the movement of analytes that can reversibly react with a selector given a product in the presence of drift. The problem mimics the movement of enantiomers in a capillary electrophoresis experiment. As is well known, the signal in the capillary must be sharp enough to make a good determination of the effective mobility of the analytes being analyzed. The essence of the technique is based on fast interconversion rates. Therefore, the effective diffusion coefficient must be negligible during the experiment. In the present work, an exact expression for both the apparent mobility and the diffusion coefficient is obtained. This is done by writing the rate equations governing the process and solving them using the generating function technique. The effective mobility coincides with the Wren and Rowe equation, whereas the diffusion coefficient allows us to determine the values of the parameters to be taken into account so that this quantity is minimal or close to zero. On the other hand, the numerical solution of the kinetic equations and Monte Carlo simulations allow us to follow the signal in the capillary and to determine its space–time evolution.