Simultaneous enantioseparation of four b 2 -agonists by capillary electrophoresis with cyclodextrin additives. Study of the enantioselective mechanism
The simultaneous capillary electrophoretic enantioseparation of adrenergic b 2 -agonists enantiomers (trantinterol, mabuterol, clenbuterol, bambuterol) was studied with b-cyclodextrin, ethyl-b-CD, methyl-b-CD, hydroxypropyl-b-CD, and hydroxyethyl-b-CD as chiral selector. The type and concentration of the chiral selector and buffer pH played a very important role in the enantioseparation of the analyzed compounds. Hydroxypropyl-b-CD was found to be the most effective complexing agent and allowed excellent chiral/achiral resolutions compared to the other CDs. The simultaneous enantioseparation of four b 2 -agonists was achieved using 100 mM citric acid -10 mM Na 2 HPO 4 buffer at pH 2.5 containing 120 mM hydroxypropyl-b-CD with an applied voltage of 20 kV. Method validation in terms of repeatability, linearity, and limits of detection and quantification was performed. The effect of structural features of analytes on R s and t m was studied. Complexation binding constants for the interactions between the four compounds and three different CDs were evaluated for elucidating the enantioseparation mechanism. It was found that very small differences in the chemical structure of the analytes resulted in significant changes in stereoselective recognition.