Study And Application Of Novel Method In MEEKC And New Method In Improvement Sensitivity Of CE

Capillary electrophoresis(CE)has emerged as a separation technique in 1980s.Due to its high resolution,efficiency,short analysis time,simplicity and low sample and solvent consumption,CE has proved to be one of active fields in analytical chemistry. In recent years,much attention has been devoted to the improvement the separation selectivity and detection sensitivity of CE.Room-temperature ionic liquids(RTILs), sometimes called molten salts,are those compounds which are liquids at room temperature or whose melting points are slightly higher than ambient temperature and consist entirely of ionic species.Generally,the ILs present a variety of desirable properties,such as low melting point,conductivity,nonflammability,air and water stable,thermal stability,and can be easily and economically prepared.Recent years, the application of ILs for the separation of various classes of compounds in CE,gas chromatography(GC)and high performance liquid chromatography(HPLC)has been recognized.Furthermore,the poor concentration sensitivity is one of the reasons of development of CE.To exert the advantages of CE and overcome the shortcoming of low sensitivity in CE,the following major innovative work was carried out in this dissertation on the basis of the previous literatures:1.A novel method on analysis of active compounds in traditional Chinese herbal by microemulsion electrokinetic chromatography with 1-butyl-3-methylimizolium tetrafluoborate ionic liquid as additive was developed for the first time.2.A new method for improving sensitivity by large-volume sample stacking combined with sweeping without polarity switching by capillary electrophoresis was developed for the first time and the concentration mechanism of discussed in detail.3.A new method of unlimited-volume electrokinetic stacking injection of alkalin in acidic solutions by micellar electrokinetic capillary chromatography was developed.The sensitivity could be improved 1000-fold with this method.This dissertation consists of six chapters.In chapter 1,the application of ILs in CE was introduced,including the physical and chemical character of ILs and its application in CE.Moreover,some new preconcnetration methods in CE were also introduced.In chapter 2,a new method for separation and determination of baicalein,baicalin and wogonin in Scutellariae radix and its preparation by microemulsion electrokinetic chromatography with 1-butyl-3-methylimizolium tetrafluoborate ionic liquid as additive was developed.Meantime,the separation mechanism was discussed.Under optimum conditions,the content of baicalein,baicalin and wogonin in Scutellariae radix and its preparation were detected.In chapter 3,a method of separation and determination of psoralen and isopsoralen by microemulsion electrokinetic chromatography was developed for the first time.In chapter 4,a new method of improving sensitivity by large-volume sample stacking combined with sweeping without polarity switching was established.The method was proved to be as a novel,simple and high sensitivity procedure to analyze trace amounts of negatively charged analytes.From 23 to 44-fold sensitivity enhancement in terms of peak area for the determined polyphenols was gained using the on-line concentration method compared with normal hydrodynamic injection, while minimizing the loss of efficiency and allowing quantitative analysis for the determination of diluted samples in low conductivity medium(water).The developed method can be applied to evaluate five water-soluble polyphenols contents in teas.In chapter 5,A novel method for the simultaneous determination of four flavones in citrus aurantium(L.)osbeck and its preparation byβ-cyclodextrin modified micellar electrokinetic chromatography was developed.Under optimum conditions, regression equations revealed linear relationships(r:0.9991-0.9998)between the peak area of each analyte and the concentration,the relative standard deviation(RSD) values of the migration times and peak areas were 1.53-1.74%,1.96-3.12%, (intra-day),and 1.72-2.13%,2.57-3.18%,(inter-day,for a 3-day period), respectively.In chapter 6,a new method of unlimited-volume electrokinetic stacking injection of alkalin in acidic solutions by micellar electrokinetic capillary chromatography was developed.From 1.41×10~3 to 1.10×10~3 -fold sensitivity enhancement in terms of peak area for the determined alkalin compounds was gained using the on-line concentration method compared with normal hydrodynamic injection,while minimizing the loss of efficiency and allowing quantitative analysis for the determination of diluted samples in low pH medium.