K. Slais, MODEL OF ELECTROPHORETIC FOCUSING IN A NATURAL PH GRADIENT MOVING IN A TAPERED CAPILLARY, Journal of chromatography, 684(1), 1994, pp. 149-161
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.