Analysis of anxiolytic drugs by capillary electrophoresis with bare and coated capillaries

The analysis of anxiolytic drugs, including barbiturates and benzodiazepines, by CE with bare and coated capillaries was investigated. Two types of CE modes, capillary zone electrophoresis (CZE) and micellar electrokinetic chromatography (MEKC) were employed for the separation of the solutes. Charged, structurally similar compounds exemplified by hypnotic drugs such as barbiturates were separated by both CZE and MEKC. Optimal separation conditions were established by varying the pH, the concentration of surfactant, the strength of the electric field, and the addition of the organic solvent. CZE provided different selectivities than those obtained by MEKC. For the separation of uncharged compounds such as benzodiazepines, MEKC was the method of choice because the structural difference conferred differences in hydrophobicity, leading to the different interaction with the micelle. Separations by CZE and MEKC with plain, bare fused-silica capillaries were compared to those with C8 and C18 coated capillaries. Although for these solutes, resolution and analysis time were comparable in the three types of capillaries, successful separation of more than 20 kinds of anxiolytic drugs as the mixture was achieved by using C8 and C18 coated capillaries as the separation medium.