NONEQUILIBRIUM THERMODYNAMIC SEPARATION MODEL IN CAPILLARY ELECTROPHORESIS

This paper describes a separation model in capillary electrophoresis ( CE) based on the entropy equation of nonequilibrium thermodynamics. We first related Delta S, the mixed entropy change of the solute system, to plate height (H) and Delta S-s, the contribution of Delta S only d ue to the net separation process, to resolution (R-s) and resolution p roduct (Pi R-s). In particular, we determined the entropy flow of the solute system, which is composed of both energetic and material exchan ge terms relating to capillary cooling and relative migrations among s olute zones, respectively. It is just the CE separation system, as ext erior surroundings, that contributes to the enhanced separation effici ency. The more the CE system (except the solute system) provides the s olute system with negative entropy flow, the better the separation eff iciency of the CE system. We also determined six thermodynamic forces and their thermodynamic fluxes corresponding to six irreversible proce sses; heat conduction, four kinds of diffusion (electrical field, axia l concentration gradient, electrophoretic dispersion and wall adsorpti on) and viscous flow, respectively. Entropy production is thus compose d of the six terms corresponding to time-dependent CE efficiency loss factors. The bigger the entropy production, the greater the loss of se paration efficiency. The objective functions were built based on the e ntropy equation of solute systems developed between CE separation effi ciency (Delta S-S) and the optimizing parameters (electrical strength, coolant temperature; the composition and concentration of buffer; the radius, length and wall adsorption of the capillary; the concentratio n, charge, molecular weight and conformation of solutes; injection con ditions, etc.). The more negative Delta S-s is, the better the separat ion efficiency. This model was supported by the results of our experim ents and data in the literature.