Effect of organic modifier concentrations on electrokinetic migrations in micellar electrokinetic chromatography

The effect of low concentrations of organic modifiers on the electroosmotic mobility, mueo, and electrophoretic mobility of the micelle, muep, mc, in micellar electrokinetic chromatography (MEKC) with sodium dodecyl sulfate (SDS) solutions was investigated. The results showed that mueo was mainly influenced by the viscosity of the running solution. A linear relationship between mueo and the concentration of the organic modifier was found in MEKC. A newly defined parameter, the mobility ratio, Rm, mc, which is the ratio of the electrophoretic mobility of the micelle to the electroosmotic mobility, and which characterizes the surface charge density of the micelle in MEKC system with organic modifiers, was introduced. A linear relationship between Rm, mc and the organic modifier concentration was observed. The parameter Rm, mc was found to be useful to investigate the changes in the micellar phase with the addition of organic modifier. The measured muep, mc values showed different and interesting characteristics among different organic modifiers.