Dependence of analyte separation on electroosmotic flow in capillary zone electrophoresis: Quantitative description by the reduced mobility

It is shown that the dimensionless reduced mobility, mu(i), which is the ratio of the effective mobility, u(eff,i), to the total mobility, u(eff,i) + u(eo), of separand i defined as mu(i) = u(eff,i)/(u(eff,i) + u(eo)) is that variable which allows to express the effect of the electroosmotic now (EOF) (with mobility u(eo)) on all separation parameters relevant for capillary zone electrophoresis quantitatively for nearly all conditions. Efficiency, selectivity, and resolution are expressed as a function of the reduced mobility. Based on this concept the influence of a certain EOF on the separation of cationic and anionic separands with different effective mobilities is discussed in detail. It is demonstrated that for cations the resolution is always reduced due to the EOF (if directed toward the cathode as usual), whereas for anions with effective mobilities larger than u(eo)/2 the resolution is enhanced, compared to the case without EOF. (C) 1998 John Wiley & Sons, Inc.