| During the past decades, capillary electrophoresis (CE) has shown to be an effective and powerful analytical technique for the enantioseparation due to its advantages, such as high efficiency and resolution, short analysis time, small sample volume requirement, low reagent consumption, flexibility, etc. It has been applied widely in biomedical, environmental, agricultural, and pharmaceutical research. Although the majority of enantioseparations have been carried out in aqueous CE, nonaqueous capillary electrophoresis (NACE) has also been proved to be a very powerful tool in enantiomer separations.In this dissertation, several dialkyltartrates/polyols-boric acid complexes were in situ synthesized by the reactions of dialkyltartrates/polyols and boric acid or its derivatives in methanolic medium. The feasibility of these complexes used as chiral selectors in NACE for the enantioseparations of six β-blockers and five β-agonists was investigated. The mechanism of chiral recognition was primarily studied. The following innovative achievements have been made:1. A chiral selector, di-n-amyl L-tartrate-boric acid complex, was in situ synthesized by the reaction of di-n-amyl L-tartrate with boric acid in a nonaqueous background electrolyte (BGE) using methanol as the medium. And a new method of chiral NACE was developed with the complex as the chiral selector for the enantioseparations of some β-blockers and β-agonists in NACE. Four chiral analytes that could not be resolved in aqueous microemulsion electrokinetic chromatography (MEEKC) with the same chiral selector obtained baseline resolutions in the NACE system.2. Twelve dialkyltartrate-boric acid complexes were in situ synthesized by the reaction of different dialkyltartrates with boric acid in methanol containing triethylamine. All of the twelve dialkyltartrate-boric acid complexes were found to have relatively good chiral separation performance in NACE. The effect of the molecular structure of dialkyltartrates on the chiral recognition of dialkyltartrate-boric acid complexes chiral selectors was investigated.3. NACE and mass spectrometry (MS) were used to study the chiral recognition mechanism of di-n-butyl L-tartrate-boric acid complex. The effects of various basic electrolytes including inorganic and organic ones on the enantioseparations in NACE were investigated.4. Three new complex chiral selectors in situ synthesized by three boric acid derivatives and di-n-butyl L-tartrate in methanol containing triethylamine were applied in NACE for the enantioseparations of some (3-blockers and β-agonists.5. Two polyols-boric acid complexes were in situ synthesized by the reaction of two polyols with boric acid in methanol containing triethylamine, respectively. Their chiral recognition effects for some P-blockers and β-agonists in NACE were investigated.This dissertation consists of seven chapters.In chapter1, the characteristic of NACE and its applications in chiral separation were reviewed.In chapter2, a chiral selector, di-n-amyl L-tartrate-boric acid complex, was in situ synthesized by the reaction of di-n-amyl L-tartrate with boric acid in a nonaqueous background electrolyte (BGE) using methanol as the medium. Then a new method of chiral NACE was developed with the complex as the chiral selector. It has been demonstrated that the chiral selector is suitable for the enantioseparations of some β-blockers and β-agonists in NACE. Some chiral analytes that could not be resolved in aqueous MEEKC with the same chiral selector obtained baseline resolutions in the NACE system. In order to achieve a good enantioseparation, the effects of di-n-amyl L-tartrate and boric acid concentration, triethylamine concentration, applied voltage, as well as capillary length was investigated.In chapter3, twelve dialkyltartrate-boric acid complexes were in situ synthesized by the reaction of different dialkyltartrates with boric acid in methanol containing triethylamine. All of the twelve dialkyltartrate-boric acid complexes were found to have relatively good chiral separation performance in NACE. The effect of the molecular structure of dialkyltartrates on the chiral recognition of dialkyltartrate-boric acid complexes chiral selectors was investigated. It was found that their chiral recognition effects in terms of both enantio selectivity (a) and resolution (Rs) were similar when the number of carbon atoms was below six in the alkyl group of alcohol moiety. The dialkyltartrates containing alkyl groups of different structures but the same number of carbon atoms, i.e. one of straight chain and one of branched chain, also provided similar chiral recognition effects.In chapter4, the MS spectra confirmed that triethylamine promoted the formation of negatively charged di-n-butyl L-tartrate-boric acid complex chiral counter ion with a complex ratio of2:1, which was the real chiral selector in the ion-pair principle enantio separations. The effects of various basic electrolytes including inorganic and organic ones on the enantioseparations in NACE were investigated. The results showed that most of the basic electrolytes tested were favorable for the enantioseparations of basic analytes using di-n-butyl L-tartrate-boric acid complex as the chiral ion-pair selector. It was found that achiral coexist counter ions (Na+for example) could form competing nonstereoselective ion-pair with the chiral selector, which changed the amount of selector available for complexation with the enantiomers and caused an undesirable resolution.In chapter5, three boric acid derivatives were used for the in situ synthesis of complex chiral selectors by reacting with di-n-butyl L-tartrate in methanol containing triethylamine. The three new chiral selectors were applied in NACE for the enantioseparations of some β-blockers and P-agonists.In chapter6, two polyols-boric acid complexes were in situ synthesized by the reaction of two polyols with boric acid in methanol containing triethylamine, respectively. It was demonstrated for the first time that two methanol insoluble polyols, D-mannitol and D-sorbitol, could react with boric acid to prepare chiral ion-pair selectors using methanol as the solvent medium.In chapter7, conclusions were made. |
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