Capillary Electrophoresis Enantioseparation With Maltose As Chiral Selector

Chrial environment is established by chiral selector added in buffer solution, which is an important method of capillary electrophoresis enantioseparation. Many kinds of carbohydrates are widely used as chrial selector for CE, in which, cyclodextrins and their derivatives are the most commonly used at present. Many noncyclic polysaccharides can also be used as chiral selectors. But study on oligosaccharides, such as maltose, used as selector is not often seen, and the study on their chiral recognition mechanisms is even more seldom.In this paper, maltose was used as chrial selector and the enantiomeric separations of ibuprofen, primaquine, trihexyphenidyl, citalopram hydrobromide and cetirizine hydrochloride citalopram enantiomers were achieved successfully. The effects on enantioseparation such as concentration of maltose (Cm), pH of buffer solution, concentration of background electrolyte and the applied running voltage were investigated in order to optimize separation. During the study, a critical concentration of maltose was observed. Distinct separations of enantiomers could only be achieved while exceeding the critical concentration and then the resolutions were linearly correlated with concentration of maltose.Furthermore, the separation mechanisms were also systematecially studied.First of all, the interaction between enantiomers and maltose was investigated in solutions with different concentrations of maltose. According to the experimental result, the binding constants and binding numbers of enantiomers and maltose were obviously stronger in high concentration maltose solutions. Based on the results, it could be proposed that maltose molecules aggregated in higher concentration maltose solutions and the interactions occurred between the maltose aggregates and enantiomers molecules.Secondly, the electric conductivity and fluorescence spectrometry methods were used for the study of maltose critical concentration. As shown by the results, along with the change of Cm, inflexions appeared in both fluorescence intensity and conductance of maltose solutions, closing to the"critical concentration"obtained in CE resolution study, which approved that the existent forms of maltose molecules in solutions changed above a critical concentration.Finally, using spectroscopic probes and nuclear magnetic resonance spectroscopy (NMR), it was proved that maltose molecules aggregated in high concentration solutions forming hydrophobic cavities.The researches on the separation mechanisms showed that there is a critical concentration of maltose, above which maltose molecules aggregate and form a kind of hydrophobic cavities. And the chiral discrimination ability of maltose results from these cavitiesm.