Study Of New Chiral Separation Methods Of Capillary Electrophoresis Based On Tartrate-Boric Acid Complex Chiral Selectors

As the two enantiomers of chiral compounds have different physiologic properties, the separation of chiral compounds has become a center of great interest and an important subset of separation science in recent years. Microemulsion electrokinetic chromatography (MEEKC) is a relatively new mode of capillary electrophoresis (CE); because of its many advantages it has been widely used in the separation of various samples including pharmaceuticals, cosmetics, health-care products, biological and environmental compounds, plant materials, and foods. Compared with its wider use in achiral separation, the application of MEEKC in chiral separation has been largely restricted due to the lack of suitable chiral selectors. In order to break the restriction of chiral selector and promote the development and application of chiral MEEKC, in-depth studies on the development of new chiral selector, the relationship between molecular structure and chiral discrimination, the mechanism of chiral recognition and other theoretical problems have been carried out in this dissertation, and the following innovative achievements have been made:1. Tartrate-boric acid complex chiral selector in situ synthesized was used in chiral MEEKC for the first time, by which good enantioseparation results were obtained.2. A stable microemulsion was prepared utilizing solid compound as an oil for the first time, and the microemulsion was used in chiral MEEKC successfully.3. The relationship between the molecular structure of tartrates and the chiral recognition of tartrate-boric acid complex chiral selectors was studied systematically for the first time; it was found that their chiral recognition effect increases with the number of carbon atoms in the alkyl group of alcohol moiety of tartrates.4. It was found for the first time that providing a hydrophobic environment by the microemulsion to strengthen the interactions between the chiral selector and enantiomers is one of the key factors for the improvement of chiral separation in MEEKC.5. The effect of the electric charge of microemulsion on the chiral separation in MEEKC was investigated systematically for the first time.6. The chiral MEEKC method using neutral microemulsion was eatablished for the first time, and the effect of electroosmotic flow (EOF) on the chiral separation with this method was investigated systematically.This dissertation consists of five chapters.In chapter 1, the characteristic of MEEKC and its application in chiral separation were reviewed.In chapter 2, di-n-butyl L-tartrate-boric acid complex chiral selector was synthesized in situ by the reaction of di-n-butyl L-tartrate with boric acid in the running buffer. Compared with di-n-butyl L-tartrate, the complex chiral selector has superior chiral recognition performance. Ten pairs of enantiomers ofβ-blockers and structurally related compounds, which can not be separated with dibutyl L-tartrate, obtained good resolution by using the complex chiral selector. The chiral discrimination mechanism of the complex chiral selector and the relationship between the chiral separation result and the molecular structure of analyte were analyzed in terms of molecular interactions. The fixation of chiral centers by the formation of five-membered rings was thought to be the key factor giving the complex chiral selector superior chiral recognition capability.In Chapter 3, the preparation of microemulsion utilizing a solid compound as oil phase was demonstrated. The solid compound di-i-butyl L-tartrate was used as chiral oil to prepare a chiral microemulsion, and the microemulsion was used for the chiral separation of P-blockers and structurally related compounds. The separation result was similar to that provided by di-n-butyl-L-tartrate, a liquid chiral oil.In Chapter 4, eight L-tartrates and a D-tartrate with different alcohol moieties were used as chiral oils to prepare chiral microemulsions, which were employed in conjunction with borate buffer to separate the enantiomers ofβ-blockers or structurally related compounds. The effect of the molecular structure of tartrates on the chiral recognition of tartrate-boric acid complex chiral selectors was investigated. It was found that the chiral recognition capability increases with the number of carbon atoms in the alkyl group of alcohol moiety of tartrates. The mean values of enantioselectivity (αenant) and resolution (Rs) for a number of analytes increase linearly with the number of carbon atoms in alkyl groups, i.e. Rs,avg=0.30 nC+0.38,αavg=0.016 nC+1.018.In Chapter 5, the effect of the electric charge of microemulsion on chiral separation in the chiral MEEKC method using tartrate-boric acid complex chiral selectors for the separation of the enantiomers ofβ-blockers was investigated. Neutral microemulsion was used in chiral MEEKC for the first time. The effect of applied voltage and EOF on the chiral separation using neutral microemulsion was studied on the basis of both theory and experiment.