Solute-solvent interactions in micellar electrokinetic chromatography: VII. Characterization of sodium cholate-sodium deoxycholate mixed-micellar systems.

Micellar electrokinetic chromatography (MEKC) systems with mixed pseudostationary phases of the bile surfactants sodium cholate (SC) and sodium deoxycholate (SDC) have been characterized by means of the solvation parameter model. The importance of characterizing systems with an appropriate set of solutes that embrace a wide range of descriptor values has been proven as they can significantly influence the value of the system constants. The fit of the solvation parameter model to the experimental log k data has been compared for each SC-SDC system when the Abraham descriptors and the Poole optimized descriptors, recently proposed, are used. In both cases, the variation in MEKC surfactant composition results in similar changes in the coefficients of the correlation equations, which in turn leads to similar information on solute-solvent and solute-micelle interactions. It is demonstrated that SDC is more hydrogen-bond acidic and hydrophobic but slightly less polarizable than SC. Systems with intermediate selectivity are obtained through mixtures of both surfactants.