Applications Of Novel Gemini Surfactants In Micellar Capillry Electrokinetic Chromatography

Capillary electrophoresis (CE) is an analytical chromatography technique in which molecules with different electrophoretic mobilities and partition capacity are separated by applying an external electric field on the capillary. CE has applied to biological analysis, drug and environmental analysis, and so on, due to its attractive features, e.g., multiform analytical mode, high efficiency, short analysis time, high sensitivity, and small sample requirement. Surfactants have been used in micellar electrokinetic capillary chromatography (MEKC) as pseudostationary phases (PSPs). When adding a surfactant at concentration above the critical micelle concentration (CMC) in running buffer, the separation mechanism of MEKC is based on the difference in electrophoretic mobility and distribution between the aqueous phase and the pseudostationary phase (PSP). The new gemini surfactant which consists of two hydrophobic chains and two headgroups attached by a spacer group, have attracted much attention in recent years. The nature of spacer group was shown to be of utmost importance in determining the chemical and physical properties of genimi. Compared with the traditional surfactants, geminis show many superior features, especially for the tunable spacer。When gemini without the spacer is used as PSP, it is necessary to consider the effect of the headgroups and the double hydrophobic chains on the interaction between the gemini pseudostationary phase and the analytes. Based on the gemini PSP with the spacer, the spacer became the important factor which affects the morphology of vesicle, the selectivity of PSP, and the EOF stabiliy.The main work of this thesis, which was based on the analysis mentioned above, is summarized as follows:1. The cationic double-chained surfactant didodecyldimethylammonium bromide (DDAB) was used as PSP in MEKC. Its performance on the three kinds of drugs, i.e., basic, acidic, and neutral drugs, was systematically investigated. Nicotine, cotinine, caffeine, lidocaine, and procaine were selected as the model basic drugs. Good baseline separation and high efficiency were obtained under the optimal separation condition that consisted of 50mM phosphate (pH 4.0) and 0.08mM DDAB. The DDAB-involved MEKC also showed superiority upon the separation of acidic drugs, amoxicillin and ampicillin. In the case of neutral compounds, a good separation of resorcinol, 1-naphthol and 2-naphthol was achieved with 0.1mM DDAB and 30% (v/v) acetonitrile present in buffer.2. The new type cationic surfactant gemini was used as stationary phase in open-tubular capillary electrochromatography (OT-CEC) in mixed organic-water solvent for CE of inorganic anions. The tunable gemini surfactants can improve the separation selectivity by varying the length of the spacer. Under the optimal conditions (0.1 mM gemini (18-10-18) in 30 mM phosphate, pH 8.0), relative standard deviations (RSDs) of migration time for anions separation were less than 1.0% and 2.5% for run-to-run and day-to-day assays, respectively. Detection limits range from 0.04 to 1.28μg/ml. The good results showed that the gemini surfactants as stationary phases have a lot of advantages, such as tunable selectivity, and simple, removable and refreshable stationary phase and so on. The gemini stationary phase may become a new type one instead of the chemical cross-linked stationary phase in OT-CEC.3. We present the first example of simultaneous separation of acidic and basic proteins using only cationic surfactants gemini 18-s-18 as PSPs. Under the optimal conditions (0.1 mM gemini in 10 mM phosphate, pH 3.0), RSDs of migration time were less than 0.76% and 2.18% for run-to-run and day-to-day assays, respectively. Each protein (except BSA) shows high efficiency (N 44 000 - 357 000 plates/m) and good recovery (91.1% - 100.4%). The recoveries of ovalbumin (OVA), hemoglobin (Hb), and human serum albumin (HAS) are above 97.2%, 88.9%, and 90.6%。4. The gemini-capped gold nanoparticles (AuNPs) were prepared and applied as the PSP for simultaneous separation of acidic and basic proteins. The integration of gold nanoparticles (AuNPs) into the gemini PSPs shortened the analysis time and improved the separation efficiency to 10 200 - 520 000 plates/m. The recoveries of OVA, Hb, and HSA in biosamples are above 94.5%, 85.4% and 92.2%, respectively. The method is also suitable for biosamples.