MODEL OF ELECTROPHORETIC FOCUSING IN A NATURAL PH GRADIENT MOVING IN A TAPERED CAPILLARY

The principle and theoretical description of zone focusing in electrop horetic migration in a tapered capillary are presented. The model invo lves moving zones which gradually reduce their volume. The variance of a single Gaussian zone is discussed to illustrate the dynamics of thi s 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 wi th a shallow taper. The relations between the departure from the local steady state, the ratio of the inlet to outlet capillary cross-sectio n, the ampholyte effective mobility and the pH gradient were establish ed. They allow a comparison of described process with conventional iso electric focusing and also the selection of the operating conditions s uch that the departure from the local steady state can be decreased to an acceptable extent. The relations predict that focusing in the capi llary with a shallow taper should maintain constant the ratio of the a ctual zone width to the local steady state width, provided that the lo cal capillary cross-section is indirectly proportional to the migratio n length coordinate. The significance of some assumptions needed for t he model formulation is analysed. Numerical examples demonstrate the f easibility of the method.