Novel Method For Capillary Electrophoresis Based On Interaction Between Ionic Liquid And Medium Components

Capillary electrophoresis (CE) is an effective analytical technique, which permits rapid, efficient separation and a small sample volume. Due to low melting point, good conductivity, wide electrochemical window, special solubility, room-temperature ionic liquids (RTILs) are widely applied in capillary electrophoresis. Imidazole ionic liquids can be absorbed into capillary wall affecting the quantity and direction of electroosmotic flow (EOF). What's more, because of its unique structure, the interactions between ILs and other molecular are listed as electrostatic forces, hydrogen bonding, van der Waals forces, dispersion forces, n-πandπ-πinteraction, and so on. As additives in buffer, it can interaction with analytes, cyclodextrin and surfactant affecting the Z/M value of analytes or distribution characteristics, which show another separation mechanism for CE. Therefore, imidazole ionic liquid is the most widely applied in CE. Summarizing the structure, properties and applications of imidazole ionic liquid, IL as additive in CE was investigated. The thesis content consists of two part. The first part is that achiral ionic liquid as auxiliary additives is utilized for separation chiral drugs. The second part is that oil-in-water microemulsion containing IL and micelles modified hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6) were introduced into microemulsion electrokinetic chromatography (MEEKC) and micellar electrokinetic chromatography (MEKC) for separation chiral or achiral compounds. The separation selectivities of the novel MEEKC and MEKC on analytes were studied. Specific contents are listed as follows:(1) A capillary zone electrophoresis (CZE) method that the enantiomers of three chiral drugs (chloramphenicol precursors, propranolol, salbutamol) were separated on condition that water-soluble achiral ionic liquid 1-butyl-3-methyl-imidazole hydrochloride ([BMIM]C1) was used as an additive,β-cyclodextrin or its derivatives as chiral selectors in buffer was established. The results indicated that the three drugs can be baseline separated in the presence of ionic liquid. However, the above enantiomers can be partly separated if there exist no ionic liquid in buffer. On this basis, the effects of chiral selector concentration, type and concentration of ionic liquid, pH in buffer and separation voltage on the separation were further investigated.(2)In order to discuss the influence mechanism of achiral IL on the separation of chiral drugs, fluorescence spectroscopy was employed to determine binding constants between the each enantiomer of precursors of chloramphenicol andβ-cyclodextrin in the presence of IL, compared with the absence of IL. From the microscopic perspective, brief analysis and discussion were made in light of the results.(3)Neutral compounds can not be achieved separation by MEEKC using a nonionic surfactant Tween-20 as surfactant. However, Tween-20 micelles can share charge by interacting with hydrophobic ionic liquid formed similar mixed micelles. A novel microemulsion, Tween-20 as surfactant and 1-butyl-3-methylimidazolium hexafluorophosphate([BMIM]PF6) as oil phase, was applied in MEEKC for separation of four neutral compounds and four fluoroquinolones . The effect of pH in buffer, ionic stength, concentration of surfactant and ionic liquid on the separation selectivity were discussed. Compared with the microemulsion containing cyclohexane as oil phase and sodium dodecyl sulfate (SDS) as surfactant, two microemulsion have differences in the distribution mechanism and separation selectivities.(4)Microemulsion containing IL was formed by using nonionic Tween-20 as surfactant and [BMIM]PF6 as oil phase. The microemulsion was introduced into MEEKC, and chiral drugs (chloramphenicol precursor and ofloxacin) were successfully separated by the novel MEEKC method under acidic conditions andβ-cyclodextrin derivatives as chiral selector. Besides, the effect of microemulsion composition on separation was investigated. The separation mechanism was briefly discussed as well. The method permits many adjustable factors, high theoretical plate number like tradition MEEKC method. Nonionic surfactant avoided inhibition of electroosmotic flow (EOF), The MEEKC method can realize separation of compounds in the acidic environment.(5) By the interaction between anionic surfactant sodium dodecyl sulfate (SDS) and hydrophobic ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, a novel micelles electrokinetic chromatography method was established. Mixture of eight kinds of quinolone drugs was successfully separated. Moreover, impacting factors on separation selectivity, such as pH, amount of surfactant and ionic liquid were discussed. The results show that the separation selectivity by using mixed micelles is different from that which SDS micelles was not modified by ionic liquid.