Study On Two Peak Phenomena In Micellar Electrokinetic Capillary Chromatography

Micellar electrokinetic capillary chromatography is one of important separation modes of capillary electrophoresis. In this thesis, two peak phenomena, which is one compound having two peaks in electropherogram were investigated and the conditions this phenomena were studied. The paper consists of five chapters.In chapter one, the elementary theory and the applications of capillary electrophoresis in the separation of bio-macromolecule, pharmaceutical analysis, the residual analysis of pesticides, online preconcentration technique, nonaqueous capillary electrophoresis and the two peak phenomena in capillary electrophoresis were reviewed.In chapter two to five, two peak phenomena in the separation of anionic, cationic components and neutral compounds were investigated when anionic surfactant cetyltrimethylaminium bromide, cationic surfactant sodium dodecyl sul-fate and nonionic surfactant polyoxyethylene-23-lauryl ether were used as micellar. The study showed that slow interaction process besides partition exists in micellar electrokinetic capillary electrophoresis and it is the slow interaction process that leads to the appearance of two peak phenomena. In addition, the relative peak area of the two peaks is concerned with the surfactant concentration in sample solution. It was found that the relative peak area of one of two peaks increased with surfactant concentration, while the other peak decreased and total area of two peaks is almost constant. The fact shows that the appearance of two peak phenomena was resulted from the interaction between surfactant and analyte.The influence of electric field on the interaction between surfactant and analyte were also studied in chapter two to five. It was shown that electric field can restrain the interaction between surfactant and analyte, and the restraint may cause thedisappearance of two peaks for some substances except neutral compounds when surfactant is not in sample.In chapter 4, it was also discovered that two peak phenomena may appear when surfactant is not added into neutral compound sample, and the cause of the phenomenon may be that hydrophobic interaction between surfactant and neutral compound is stronger than the restrain of electric field.Comparing the molecular structure of surfactant with that of component, it was shown that the formation of two peaks depends on both the analyte and the surfactant.The influences of time and temperature on the formation of two peaks are the other parts of work. It was found that it took about from several hours to hundreds of hours to convert two peaks from the interaction of surfactant and analyte to single peak. And it takes very long time for the interaction to the equilibrium when the charge polarity of surfactant is same as that of analyte. Temperature can accelerate interaction process. From the infrared and nuclear magnetic resonance spectra of the product which was from the interaction between cetyltrimethylaminium bromide and m-hydroxyl benzole acid, they also presented evidences for the appearance of new compound. Finally, suggestions to avoid two peak phenomena were proposed.