Enantiomeric separation of clenbuterol by transient isotachophoresis-capillary zone electrophoresis-UV detection - New optimization technique for transient isotachophoresis

A method for the in-line preconcentration and enantioseparation of clenbute rol by transient isotachophoresis-capillary zone electrophoresis-UV absorba nce detection (transient ITP-CZE-UV) has been developed. It implies the use of dimethyl-beta-cyclodextrin as chiral selector and the application of a hydrodynamic counterflow during the ITP step. ITP is used to focus the samp le constituents prior to CE whereas a counterpressure counterbalances the e lectrophoretic migration of the compounds. The sample is then focused and k ept stationary in the proximity of the capillary inlet before CZE separatio n, leading to an extended-volume ITP-CZE system. A new strategy for the fas t optimization of the counterpressure has been developed which implies the measurement of the hydrodynamic and electrophoretic velocities of the analy te during ITP. The in-line preconcentration and enantioseparation of clenbu terol selected as model compound was optimized using this method. Salbutamo l was chosen as internal reference in order to check the reproducibility of the method. A. 173-nl volume of aqueous sample solution was injected which implies an improvement of the injection volume of about 16 and a resolutio n of 4.8 was obtained for the clenbuterol enantiomers. A concentration dete ction limit of 10(-6) mol/l was readily achieved for clenbuterol and salbut amol using only 3 min ITP preconcentration in in-line counterflow transient ITP-CZE-UV. Thanks to its fast optimization, the method is applicable to a ny enantioseparation by means of only five very short preliminary measureme nts. (C) 2000 Elsevier Science B.V. All rights reserved.