| Electrokinetic chromatography can separate charged and un-charged, hydrophilic and lipophilic substances simultaneously. Ionic liquid (IL) , known as green solvents, is a new class of molten salt with the melting point close to or below room temperature[1]. In the recent years, IL has received more attentions thanks to negligible vapor pressure, good thermal stability and high electrical conductivity. Based on the unique physicochemical property, IL were applied widely in capillary electrophoresis. At present, the applications and separation mechanism of IL in capillary zone electrophoresis (CZE) were more intensively studied. Many applications of IL in micellar electrokinetic chromatography (MEKC) was reported, but most of them were concentrated on the optimizing experimental conditions to improve separation, the separation mechanism of IL improving MEKC was not very well studied. There were no reparts about effects of IL on micellar microstructures. The effects of IL on microemulsion properties were reported, but there were few reports ahout the applications of IL in microemulsion electrokinetic chromatography (MEEKC). Investigation of the separation mechanism about IL improving MEEKC and effects of IL on microemulsion microstructures have been not reported. In view of this, this thesis studied the effects of IL on micellar and microemulsion microstructures to evalue these impacts on separation mechanism. The thesis mainly included the following three parts.1.Effects of ionic liquid on micellar microstructures and separation performance in micellar electrokinetic chromatography (MEKC) were investigated. The experimental results showed that adding ionic liquid into the micellar system would result in a decreased micellar surface charge density, an enlarged size of micelle and a slight enhancement of polarity in inner core of micelle. Prednisone, hydrocortisone and prednisolone were analyzed with MEKC to evaluate the separation performance. Hydrocortisone and prednisolone could not be separated in SDS micellar system. In the mixed system of ionic liquids and SDS (20 mmol/L SDS-10 mmol/L 1-butyl-3-methyl iminazolium tetrafluoroborate -50 mmol/L borax pH 8.4), the three analytes could be baseline separated within 17 min. Notably, the linearity ranged from 2 to 100 mg/L, and the detection limits based on ratio of signal to noise of 3 were 1.0, 1.1 and 1.0 mg/L for three analytes respectively. The method has been used to analysis of corticosteroids in cosmetic samples, the recoveries for three analytes were between 95.1% and 117%. This method is of simple pretreatment, accuracy, reproducibility, and could be applied to the quality control of cosmetics.2. Effects of ionic liquid on microemulsion microstructures and separation performance in microemulsion electrokinetic chromatography (MEEKC) were investigated. The experimental results showed that adding ionic liquid into the microemulsion system would result in a decreased surface charge density and size of microdroplets decreased, and a slight enhancement of polarity in inner core of microemulsion. Prednisone, hydrocortisone, prednisolone, hydrocortisone acetate, cortisone acetate, prednisolone acetate and triamcinolone acetonide were analyzed with MEEKC modified with IL to evaluate the separation performance. Cortisone acetate and prednisolone acetate could not be separated in typical microemulsion system including 3.3% SDS, 6.6% n-butanol, 0.8% n-octane and 50 mmol/L borax pH 8.7. Adding 10 mmol/L 1-butyl-3-methyl iminazolium tetrafluoroborate into microemulsion system,the seven analytes could be baseline separated within 28 min. Notably, the linearity of hydrocortisone, prednisolone and triamcinolone acetonide ranged from 5 to 200 mg/L and the linearity of prednisone, hydrocortisone acetate, cortisone acetate and prednisolone acetate ranged from 5 to 100 mg/L,and the detection limits based on ratio of signal to noise of 3 were 2.0,2.0,1.9,3.5,3.3,3.4å'Œ2.8 mg/L for seven analytes respectively. The method has been used to analysis of corticosteroids in cosmetic samples with simple extraction pretreatment, the recoveries for seven analytes were between 86% and 114%, RSDs of migration time and peak areas were less than 1.8% and 5.0 %(n=7)respectively. This method is of accuracy, reproducibility, simplicity for pretreatment, and could be applied to the quality control of cosmetics.3. Effects of ionic liquid on microemulsion stability, microstructures and separation performance in microemulsion electrokinetic chromatography (MEEKC) were investigated. The experimental results showed that ionic liquid could enhance surface activity of the surfactant sodium dodecyl sulfate (SDS) and promote the formation of microemulsion. The experimental results showed that adding ionic liquid into the microemulsion system would result in decrease of surface charge density and size of microdroplets, and a slight enhancement of polarity in inner core of microemulsion. Compared to typical microemulsion in MEEKC, a low content of 1.4% SDS microemulsion system, by adding 10 mmol/L 1-butyl-3-methyl iminazolium tetrafluoroborate and increasing n-butanol to 10%, could stabilze. Prednisone, hydrocortisone, prednisolone, dexamethasone, hydrocortisone acetate, prednisolone acetate and triamcinolone acetonide could be baseline separated within 15 min. Notably, the linearity of prednisone ranged from 2 to 500 mg/L, the linearity of hydrocortisone and prednisolone ranged from 2 to 100 mg/L, the linearity of dexamethasone ranged from 2 to 200 mg/L and the linearity of hydrocortisone acetate, prednisolone acetate and triamcinolone acetonide ranged from 5 to 100 mg/L,and the detection limits based on ratio of signal to noise of 3 were 1.6,1.2,0.8,1.4,3.8,3.5 and 2.6 mg/L for seven analytes respectively. The method has been used to analysis of corticosteroids in cosmetic samples with simple extraction pretreatment, the recoveries for seven analytes were between 87.6% and 115%, RSDs of migration time and peak areas were less than 1.6 % and 5.0 %(n=7)respectively. This method shortened the analytical time dramatically. |
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