Capillary Electrophoresis Velocity Gap Mode Developed For Enantioseparations

Capillary electrophoresis(CE) is one of the commonly used methods in separationof chiral drugs, in which one/mixed selectors are added into the backgroundelectrolyte. Two enantiomers form complexes with the chiral selector. Based ondifferent interactions with the chiral selector, the enantiomer complexes migrate witha velocity difference, leading to the chiral separation. An efficient chiral selector iscritical for achieving the sufficient chiral separation using conventional CE method.Here we propose velocity gap mode of CE (VGCE) method to performhigh-resolution chiral separations without using an efficient chiral selector. The newapproach utilize two consecutive electric fields to creat two motion phases of analytesin a capillary. By adjusting the field strengths ratio of the first motion phase andsecond motion phases, the velocity difference between two analytes is significantlyincreased. To prove the universality of VG mode, chiral separations ofchlorpheniramine and promethazine are performed. Chiral separations of analytes areperformed in conventional CE first as control experiments. All analytes are partlyresolved in conventional CE method. By contrast, under the same conditions (BGE,the chiral selector, the efficient separation length, etc.), the analytes are baselineresolved using VGCE. The resolution of terbutaline increase from1.39to5.26,chlorpheniramine increase from1.24to4.12and promethazine hydrochloride increasefrom1.21to4.79. Purity test of the enantiomers separated by the new approach isinatially confirmed, and there are almost no impurities in the two enantiomers peak.All results indicate that VGCE could perform high-resolution chiral separations, eventhough using an inefficient chiral selector.