Separation of Various Positional Isomers of Aromatic Anions by Nonionic Micellar Electrokinetic Chromatography Coupled with Ion Association Distribution Toshio Takayanagi, Kana Fushimi, Shoji Motomizu Department of Chemistry, Faculty of Science, Okayama Uni  ersity, 3-1-1 Tsushimanaka, Okayama, 700-8530, Japan Received 30 August 1999; accepted 5 November 1999 Abstract: Separation of positional isomers of aromatic anions was studied by micellar electrokinetic chromatography using nonionic surfactants andor an ion association reagent. The isomers were well resolved by adding nonionic surfactant in the migrating solution, which indicates that binding of the anions to a nonionic surfactant micelle is different among the isomers. The apparent electrophoretic mobility of the anions decreased with increasing concentrations of the surfactants in the migrating solution, and the binding phenomena are analyzed from the electrophoretic mobility change. Addition of an ion association reagent in the migrating solution also changed the resolutions. Some binding constants of the ion associates are also determined through the mobility change.  2000 John Wiley & Sons, Inc. J Micro Sep 12: 107 112, 2000 Key words: nonionic surfactant; micellar electrokinetic chromatography; ion associa- tion; positional isomer; aromatic anion INTRODUCTION Ž . Micellar electrokinetic chromatography MEKC with anionic surfactants has been proved to be a powerful technique for the separation of non- charged substances in capillary zone electrophoresis Ž .   CZE 1,2 . In addition to the anionic surfactants,    zwitterionic surfactants 3 , cyclodextrin 4,5 , and   organic solvents 6,7 have been used for the separa- bility improvement in combination with the anionic surfactants. Nonionic surfactants were also exam- ined as a modifying reagent for the MEKC separa-   tions 8  11 . Recently, Matsubara and Terabe demonstrated the separability improvement of an- ionic dansylamino acids by a MEKC method with   nonionic surfactants 12 . In the method, the hy- drophobicity of analytes was considered to con- tribute to the distribution of the analytes between Presented at the 22nd International Symposium on Cap- illary Chromatography and Electroelectrophoresis, Gifu, Japan, November 8  12, 1999. Correspondence to: Toshio Takayanagi; e-mail: takayana @cc.okayama-u.ac.jp. the micelle and water. The MEKC with nonionic surfactants also has a prominent advantage that high concentrations of surfactants are allowed without any increase in the electric current. Although the MEKC separation of ionic substances using non- ionic surfactants possesses several advantages, it should be necessary for designing separation systems to clarify the interaction between analytes and the surfactants in the migration systems. In this study, the authors aimed at characteriz- ing the interaction by analyzing the binding phenom- ena when some aromatic anions and nonionic sur- factants were used as a model analyte and a micellar reagent, respectively. The degree of the interaction was analyzed using the change in electrophoretic mobility of the analyte anions. Ion association reac- tions between a quaternary ammonium ion and the analyte anions were also utilized in the presence of nonionic surfactant micelle for improving the sepa- rability, where a nonionic surfactant micelle can act as a hydrophobic medium to which the ion associ- ates formed can distribute. Some binding constants of the ion associates to the micelles were also deter- mined by using the mobility change. Ž. Ž . J. Microcolumn Separations , 12 2 107 112 2000  2000 John Wiley & Sons, Inc. 107