Enantioseparation of Three β-Agonists Using Di-n-butyl d-Tartrate-Boric Acid Complex as Chiral Selector by Means of MEEKC

Abstract

In this study, a self-prepared complex chiral selector, di-n-butyl D-tartrate-boric acid complex, by the reaction of di-n-butyl D-tartrate with boric acid in a running buffer was used as a chiral selector for the enantiosepara- tion of three b-agonists including clenbuterol, cyclo- clenbuterol and tulobuterol by means of microemulsion electrokinetic chromatography (MEEKC). Three b-ago- nists were successfully enantioseparated using the chiral system, indicating that the di-n-butyl D-tartrate-boric acid complex was a useful chiral selector. The effects of di-n- butyl D-tartrate and sodium tetraborate concentration, sur- factant concentration, cosurfactant, phosphate, buffer pH and composition, as well as applied voltage were exten- sively investigated to achieve a good enantioseparation. The di-n-butyl D-tartrate and sodium tetraborate concen- tration in the running buffer had great influence on the chiral resolution (Rs). Three b-agonists which could not be separated with only di-n-butyl D-tartrate, obtained good chiral separation using the complex chiral selector; among them, two pairs including clenbuterol and cycloclenbuterol could be baseline resolved in 7 min under optimized experimental conditions of 0.8% (w/v) di-n-butyl D-tar- trate, 40 mM sodium tetraborate, 3.0% (w/v) Tween-20 and 60 mM sodium dihydrogen phosphate with 25 kV as running voltage. The results indicated that the method could be used for the enantioseparation of three b-agonists.