| Microemulsion electrokinetic chromatography(MEEKC) is a new electrodriven separation technique which was developed on the basis of micellar electrokinetic chromatography(MEKC). Rhamnolipid is a kind of biosurfactant with high surface activity which has been studied and applied wildly in recent years. High concentration ionic surfactants used in the traditional MEEKC system would lead to high joule heat, poor efficiency and long analysis time. We firstly applied rhamnolipid in MEEKC in order to resolve the above problems. The thesis mainly includes the following four parts.1. The rhamnolipids used in the study were extracted and purified from the fermentation broth of Pseudomonas aeruginosa. The composition and the relative mass fraction of the homologues were analyzed by high-performance liquid chromatography-electrospray ionization-mass spectrometry(HPLC-ESI-MS). The surface activity was studied by determinating its critical micellization concentration(CMC). The results showed that the rhamnolipid extract was composed of nine homologues at least. Under weak alkaline conditions(pH 7.5-9.0), pH value had significant effect on its surface activity. When pH was lower than 9.0, the CMC decreased as pH increased and reached a minimum at pH 9.0. At a pH higher than 9.0, the CMC increased gradually as pH increased. This was as a result of a joint effect of hydrogen bonding and electrostatic repulsion between polar head groups.2. The microemulsion was prepared with the rhamnolipid extract. The effect factors on the stability of the microemulsion was studied. The effects of pH value and additives on the microemulsion microstructure were evaluated by considering particle sizes and zeta potential of microdroplets. The results showed that the temperature, pH value, surfactant concentration and the cosurfactant addition significantly affected the microemulsion stability. Both the microdroplet size and absolute value of zeta potential tended to increase as the pH increased except at pH 9.0. By adding a small quantity of sodium dodecyl sulfate(SDS) to the microemulsion system, the particle size and the absolute value of zeta potential increased. The addition of low concentration n-butanol increased the particle size and decreased the absolute value of zeta potential.3. Rhamnolipid microemulsion was firstly applied in MEEKC and a novel system was established. The effects of the microemulsion composition and the electrophoresis condition on the migration window were studied systematically. Taking acetonitrile as the electroosmotic flow marker and phenanthrene as the microdroplets marker, the migration window was studied. The results showed that the migration window of microdroplets had an increasing tendency by increasing pH value, rhamnolipid concentration, borax concentration and the addition of n-butanol. We can adjust the migration window in the application work to get good separation.4. Rhamnolipid microemulsion was applied in MEEKC for simultaneous separation of prednisone, prednisolone and hydrocortisone. The separation effect was compared with the traditional MEEKC system. The optimized microemulsion system composition was 0.1%(W/W)rhamnolipid-0.8%(W/W)n-heptane-99.1%(W/W)80 mmol/L borax buffer(pH 9.2). The pH value and the running buffer concentration played the most important roles in the separation selectivity. With voltage of 20 kV and the column temperature of 20℃, three glucocorticoids were baseline separated within 9.6 min. The RSD values(n= 6)of migration time and peak area of three analytes were less than 0.9% and 3%, showing high reproducibility. Compared to the traditional MEEKC system, the separation time was effectively shortened by using rhamnolipid microemulsion system.
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