Model of electrophoretic focusing in a natural pH gradient moving in a tapered capillary

Abstract

The principle and theoretical description of zone focusing in electrophoretic migration in a tapered capillary are presented. The model involves moving zones which gradually reduce their volume. The variance of a single Gaussian zone is discussed to illustrate the dynamics of this process. In order to derive the solution of the continuity equation, previous models of idealized focusing of ampholytes were modified to represent zone electrophoretic focusing in migration in a capillary with a shallow taper. The relations between the departure from the local steady state, the ratio of the inlet to outlet capillary cross-section, the ampholyte effective mobility and the pH gradient were established. They allow a comparison of described process with conventional isoelectric focusing and also the selection of the operating conditions such that the departure from the local steady state can be decreased to an acceptable extent. The relations predict that focusing in the capillary with a shallow taper should maintain constant the ratio of the actual zone width to the local steady state width, provided that the local capillary cross-section is indirectly proportional to the migration length coordinate. The significance of some assumptions needed for the model formulation is analysed. Numerical examples demonstrate the feasibility of the method.