Optimization of Micellar Electrokinetic Chromatography

Abstract

The separating power of micellar electrokinetic chromatography (MEC) for neutral solutes Is critically examined. A theory for the optimization of resolution (Rs) and resolution per unit time (Rs/tR) is presented and evaluated. Equations are derived that pretfct the optimum retention factor (k') and the corresponding surfactant concentration to use. Another equation is derived that relates the analysis time to five parameters: Rs, α (selectivity), k',tc/tmc, and H/veo(plate height/electroosmotic velocity). The capacity factor for the best resolution Is given by k'=(tmc/to)1/2, where to and tmc are the retention times of the aqueous and micellar phases, respectively. The capacity factor for the best resolution per unit time ranges from 1.2 to 2. The separations obtained by using the optimum capacity factor for resolution per unit time instead of resolution may be slightly poorer in terms of resolution but are much faster. Provided the optimum conditions are employed, the quality of MEC separations is independent of the solute hydrophobicity. The advantages of a surfactant gradient for the separation of solutes with a wide range of hydrophobicities are discussed. A brief comparison of MEC, micellar liquid chromatography, and conventional high-performance liquid chromatography is also made. © 1990, American Chemical Society. All rights reserved.