Investigations on the behaviour of acidic, basic and neutral compounds in capillary electrochromatography on a mixed-mode stationary phase

This work describes the separation of acidic, basic and neutral organic com pounds as well as inorganic anions in a single run by capillary electrochro matography employing a stationary phase which exhibits both strong anion-ex change and reversed-phase chromatographic characteristics. The positive sur face charge of this stationary phase provided a substantial anodic electroo smotic flaw. The analytes were separated by a mixed-mode mechanism which co mprised chromatographic interactions (hydrophobic interactions, ion-exchang e) as well as electrophoretic migration. The influence of ion-exchange and hydrophobic interactions on the retention/migration of the analytes could b e manipulated by varying the concentration of a competing ion and/or the am ount of organic modifier present in the background electrolyte. Additionall y the effects of pH changes on both the chromatographic interactions as wel l as the electrophoretic migration of the analyles were investigated. (C) 2 000 Elsevier Science B.V. All rights reserved.