Application of electrokinetic chromatography to pharmaceutical analysis.

Electrokinetic chromatography (EKC) is one branch of capillary electrophoresis that permits the separation of electrically neutral solutes by the electrophoretic technique. The separation principle of EKC is based on that of chromatography, and various modes of EKC have been developed along with the partition mechanism. Micellar electrokinetic chromatography (MEKC), in which an ionic surfactant solution is employed instead of a buffer solution in capillary zone electrophoresis (CZE) at a higher concentration than the critical micelle concentration (CMC), has become the most popular technique among various EKC modes. Besides the separation of the electrically neutral or non-ionic solutes, MEKC is also effective for the separation of ionic solutes as well as CZE, hence it suits the analysis of pharmaceuticals, including cationic, anionic and neutral. Separation selectivity in MEKC can be manipulated easily through the modification of the buffer as well as changing the surfactants. Direct enantiomeric separation is successful by using chiral surfactants or chiral additives. Determination of drugs in plasma is also successfully achieved by a direct sample injection method, similar to micellar HPLC. In this paper, we summarize the principle separation characteristics of MEKC and some applications to pharmaceutical analysis, including direct enantiomeric separation and direct assay of drugs in plasma.