The mathematical model outlined in Part I is recast in a form suitable for numerical computation. The spatial derivatives are replaced by finite-difference expressions, which leads to a set of ordinary differential equations coupled to a set of nonlinear algebraic relations. This system is solved using existing integration techniques. The resulting algorithm simulates the characteristic behavior of the classical modes of electrophoresis, which is shown by examples involving moving boundary electrophoresis and isoelectric focusing. In the first example two different integration schemes are used and their accuracy and stability investigated. The second example illustrates the versatility of the methodology. 0. SCOPEIn the model presented in Part I (Saville and Palusinski), the electrophoresis of amphoteric compounds is described by a set of partial differential equations coupled to a system of algebraic equations. Separation of sample components arises from interactions between the chemical equilibria and the transport processes. These interactions alter the effective mobilities of the various species and induce them to separate under the action of the electric field in nonequilibrium processes such as isotachophoresis. In equilibrium processes such as isoelectric focusing, the action of the field produces a pH gradient and the amphoteric constituents move to positions where they are isoelectric. In either case, the evolution of the process is best followed by numerical methods. The purpose of this paper is twofold: 1. To show how the mathematical model derived in Part I can be expressed in a form suitable for numerical computation. 2.To demonstrate the model depicts the detailed characteristics of electrophoretic processes.The numerical algorithm selected employs a five-point finite-difference expression to approximate the spatial derivatives at a set of mesh points. This converts the set of partial differential equations into a set of ordinary differential equations describing the temporal evolution of the concentration fields at each mesh point. These equations can be integrated using any one of a variety of schemes for solving sets of firstorder ordinary differential equations. Boundary conditions at either end of a separation column are incorporated by adjusting the form of the finite-difference expressions at the boundary points. In a similar fashion, the algorithm can easily be adapted for simulation of novel separation methods such as the use of immobilized ampholytes, molecular sieving, or ion-selective membranes at the boundaries. CONCLUSIONS AND SIGNIFICANCEThe implementation of the algorithm describing electrophoretic transport processes is illustrated by simulating moving boundary electrophoresis and isoelectric focusing with immobilized species. Both examples are intended to illustrate particular electrophoretic processes using rather simple systems. Attention concentrates on the essential characteristics of a particular mode, For the isoelectric focusing example, the central feature is the migration...

Two methods which utilize simple buffers for the generation of stable pH gradients useful for preparative isoelectric focusing are compared and contrasted. The first employs preformed gradients comprised of two simple buffers in density-stabilized free solution. The stability of this system is analyzed theoretically and by computer simulation. These precast gradients are limited to two buffering components, subject to diffusion, and restricted to the neutral pH region. An experimental application is presented. The second method utilizes neutral membranes to isolate electrolyte reservoirs of constant composition from the separation column. It is shown by computer simulation that steady state gradients can be formed at any pH range with any number of components in such a system.

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