DETERMINATION OF DIFFUSION-COEFFICIENTS AND SEPARATION NUMBERS IN MICELLAR ELECTROKINETIC CHROMATOGRAPHY

Diffusion coefficients in micellar electrokinetic chromatography (MEKC ) were determined for a homologous series of alkylaryl ketones. Overal l diffusion coefficients in micellar electrolyte systems were calculat ed from measured spatial peak variances, using the stopped migration m ethod. From overall diffusion coefficients at two different surfactant concentrations, diffusion coefficients in the aqueous phase and in th e micellar phase, respectively, were determined. Diffusion in the mice llar phase was found to be approximately one order of magnitude lower than diffusion in the aqueous phase for the alkylaryl ketones. The inf luence of micellar diffusion on efficiency is treated theoretically. I t is demonstrated that efficiency in MEKC strongly depends on the rete ntion factor, especially for small values of the elution window. Under practical MEKC conditions, however, the influence of micellar diffusi on is of minor importance. The determination of separation numbers in MEKC is evaluated and their use as parameter for the separation perfor mance is discussed.