Separation of Fat-soluble Isoquinoline Enantiomers using β-Cyclodextrin-modified Micellar Capillary Electrokinetic Chromatography

In this paper, chiral fat-soluble enantiomers of 1-phenyl-R, S-tetrahydrogen isoquinoline (ER, ES) are rapidly separated using beta-cyclodextrin (beta-CD) modified micellar capillary electrokinetic chromatography coupled with electrochemical detection (EC). An effectual micellar suspension of 35 mmol/L phosphate buffer saline (PBS) (pH 7.85) containing 30 mM sodium deoxycholate, 20 mM beta-CD and 20% (v/v) acetonitrile was developed as the running buffer. Among them, the surfactant sodium deoxycholate formed the micelles in the buffer, beta-CD was employed to improve the separation, and the acetonitrile acted as an organic modifier. After the optimization of the factors such as detection potential, separation voltage, sampling time and the composition of running buffer, baseline separation was obtained within 12 min at 20 kV of separation voltage. The RSD (n = 5) of migration times and peak areas of the analytes are 2.3% (ER), 2.7% (ES) and 2.0% (ER), 3.5% (ES), respectively. The detection limit is 0.5 mu mol/L for ER and 0.2 mu mol/L for ES, also it was found that trace ER could be detected at the limit proportion of ER to ES for 1: 500. This protocol was successfully applied for monitoring the amount of ER from ES in synthetic drug intermediate.