Resolution, load capacity and separation efficiency in isotachaphoresis are experimentally evaluated and the results are compared with the theoretically expected values. The theoretical and experimental results show good agreement and confirm the reliability of the transient-state model. The importance of the dimensionless separation number and load capacity for the determination and standardization of experimental performance conforms with theory. It is shown that, in view of these two parameters, the pH of the leading electrolyte is the best rationale for optimization, whereas the pH of the sample has only restricted possibilities. Steady-state configurations in which constituents are not migrating in order of decreasing effective mobilities are shown and discussed.