High performance capillary electrophoresis (HPCE) has emerged as a newseparation technique in 1980s. Comparing with high performance liquidchromatography (HPLC), it has the advantages of high resolution, high efficiency,short analysis time, simplicity and low sample and solvent consumption. The theoryand application research of CE has proved to be one of the most active fields inanalytical chemistry. However, one serious drawback of CE is the low concentrationsensitivity which is associated with the limited optical path length for on-line UVdetection and the very small amount of sample that can be injected into the capillary.Although low detection limit of quantity can be obtained with current UV detector, thedetection limit of sample concentration is still high, which limits the applications ofCE in the analysis of trace elements in real samples. So far, how to improve thesensitivity of CE is still one of the leading questions that analytical workers attentionedIn order to further improve the concentration sensitivity of CE, making it satisfy theanalysis of trace elements in complex samples, the following major innovative workwas carried out in this dissertation on the basis of the previous literatures:1.Two on line sample concentration methods for the determination of six flavonoidsin Fructus aurantii Immaturus were developed by micellar electrokineticchromatography(MEKC) for the first time. And the two methods were systemicallycompared. The conception of anion selective electrokinetic injection and a waterplug-sweeping with reverse migrating micelles (ASIW-sweep-RMM) was broughtforward for the first time2. Two on-line sample concentration techniques, sample stacking and sweepingunder reversed polarity were thoroughly evaluated in microemulsion electrokineticchromatography (MEEKC) using pH-suppressed electroosmotic flow. Theexperimental phenomena were reasonably explained. Based on the experimentalphenomena, the conception of stacking with anion selective electrokinetic injectionand a water plug in a reverse-migrating microemulsion (SASIW-RMME) was putforward for the first time. 3.A novel method by assisting low temperature bath and high conductivity zonewith MEKC stacking was established for the determination of phenolic acids in coffeepowder for the first time. The detection sensitivity of CE was greatly improved withthe aid of the two techniques. Furthermore, the low temperature bath and highconductivity zone were successfully combined on one capillary, and the sensitivity wasfurther improved.4. A new method for the analysis of liensinine (LIE), isoliensinine (ISO) andneferine (NEF) in embryo of the seed of Nelumbo nucifera Gaertn by MEKC withcationic surfactant (TTAB) and internal standard (tetrahydropalmatine) was developedfor the first time. By using internal standard, the accuracy of the analyte quantitationwas improved. And the detection limits of the three analytes were greatly improved byusing a simple on-column preconcentration technique.This dissertation consists of six chaptersIn chapter 1,the necessity of using preconcentration techniques in CE was firstsimply set forth. Then the on-line concentration methods of CE and their applicationsin the recent ten years were detailedly introduced. And the new concentration methodsunder reversed voltage and their applications in CE were reviewed.In chapter 2, two on-column preconcentration techniques named stacking withreverse migrating micelles (SRMM) and anion selective electrokinetic injection and awater plug-sweeping with reverse migrating micelles (ASIW-sweep-RMM) weredeveloped. Using six flavonoids as model compounds, the experimental parametersthat affected the separation and stacking effect were investigated. The performance ofthe two preconcentration methods was systematically compared. The stacking factorsof peak height for the six model analytes were 13～16-folds and 13～31-folds forSRMM and ASIW-sweep-RMM, respectively. ASIW-sweep-RMM has beensuccessfully applied to the determination of the six flavonoids in Fructus aurantiiImmaturus.In chapter 3, two sample preconcentration methods-sample stacking and sweepingin MEEKC were established. And the concept of stacking with anion selectiveelectrokinetic injection and a water plug in a reverse-migrating microemulsion (SASIW-RMME) was brought forward. The retention factors of the six model analytesin the microemulsion were determined. The sweeping method has been applied to thedetermination of the six analytes in Fructus aurantii Immaturus.In chapter 4, a novel MEKC method for the determination of liensinine (LIE),isoliensinine(ISO) and neferine (NEF) in embryo of the seed of Nelumbo nuciferaGaertn was developed using tetradecyltrimethyl ammonium bromide (TTAB) asmicelle and tetrahydropalmatine (TET) as internal standard (IS). The method resultedin excellent linearity, with correlation coefficient of regression equation of 0.9997,0.9997 and 0.9992 for LIE,NEF and ISO, respectively by peak ratio between analyteand IS versus sample concentration. The repeatability of migration time, peak heightand peak area was greatly improved by IS method. Simultaneously, the detectionsensitivity was improved using large volume sample stacking (LVSS) method. Underthe optimum conditions, the stacking factors of peak height for the three analytes canreach to 20-folds.In chapter 5, new methods for the determination of chlorogenic acid (CGA), caffeicacid (CA) and ferulic acid (FA) in coffee powder were established by combination lowtemperature bath and high conductivity zone with traditional MEKC stacking method.The detection sensitivity was improved 2.1～5.4-folds comparing with conventionallarge volume sample stacking method in MEKC. Furthermore, low temperature bathand high conductivity zone were combined on one capillary to investigate thesynergism effect of the two stacking methods. These methods have been successfullyapplied to the determination of the three analytes in nestle coffee.In chapter 6, a new CZE method for the separation and determination of acetic acidand chloroacetic acids in water was established. Potassium by drogen phthalate wasused as indirect UV absorber, methyl tert-butyl ether (MTBE) was used as sampleoff-line liquid-liquid extraction solvent. The dissociation constants of acetic acid andmonochloroacetic acid were determined using neutral marker and the signal of currentchange. And their dissociation constants obtained using linear and non-linearregressions were consistent with reference on the whole