A new method to influence the separation selectivity of inorganic cations in capillary electrophoresis is presented. This method combines the use of certain crown ethers to form complexes with a specific cation (changing its ionic radius/charge ratio and thereby its electrophoretic mobility) with partitioning of the crown ether/analyte complex between an aqueous phase and a pseudo-stationary phase, such as the oil droplet of a microemulsion. Several microemulsions, including uncharged oil droplets and oil droplets with different degrees of surface charge were tested to evaluate their ability to improve the separation of the selected analytes.