Evaluation and characterization of pseudo-stationary phases in micellar electrokinetic chromatography

Abstract

The separation mechanism of neutral species in Micellar Electrokinetic Chromatography (MEKC) is based on differences in the partitioning between the aqueous mobile phase and the pseudo-stationary micellar phase [1, 2]. An important feature of MEKC is its flexibility. The composition of the electrolyte system can easily be changed in order to control migration behaviour and optimize selectivity. In this respect the pseudo-stationary phase plays a key role, since its chemical nature has a major influence on the separation process. Various surfactant systems can be used as well as mixed micelles, possessing different solubilization characteristics. Despite the ease of varying the experimental conditions, Proper selection of a suitable surfactant system in MEKC is still a difficult task. In gas chromatography stationary phases can be chosen on the basis of specific selective chemical interactions using the Rohrschneider-McReynolds scale [3], whereas in liquid chromatography mobile phases can be selected based on Snyder's selectivity triangle [4]. At present, however, the influence of the chemical nature of the pseudo-stationary phase and the structural properties of solutes on solute-micelle interactions in MEKC is still not well understood. Terabe and Okada studied the solubilization characteristics of several surfactant systems by the determination of thermodynamic quantities [5]. Recently, Yang and Khaledi applied Linear Solvation Energy Relationship (LSER) modelling for the characterization of solute-micelle interactions [6, 7]. LSER studies are also based on a thermodynamic approach and provide quantitative information about different solute-micelle interaction phenomena. They can be used to elucidate which mechanisms play a dominant role in