Two New Mechanisms For On-capillary Enrichment Of Cationic Organic Compounds With Switchable States

Capillary electrophoresis(CE) is an important technique for its high separation efficiency, short analysis time. In order to improve the sensitivity of CE, the method which based on on-capillary enrichment technique has been one of the hot researches and focus. In this study, we established two new mechanisms for on-capillary enrichment of cationic organic compounds with switchable states, aimed at improving the UV detection sensitivity of CE and developing a simple, rapid and environmentally friendly method. The paper will be divided into three chapters. Its content is as follows:Chapter 1: Introduction. Frist, a brief introduction of the background theory and principles of the CE is presented. The second, it introduces the development and applications of on-capillary enrichment techniques in the capillary electrophoresis in recent years. And the paper thought for on-capillary enrichment of cationic organic compounds with switchable states is pointed out at end of the review part.Chapter 2: In this work, we performed a new mechanism of pH-mediated stacking for analysis cationic organic compounds with switchable states. The new mechanism not only changes the pH value of sample zone to reduce the conductivity of sample zone, but also the changes in pH may cause switch the charged states of analysis, which changes the migration rate to achieve on-capillary enrichment. The mechanism has the advantage of the convenient operation, time saving and environmental friendly. In our work, we used the anilines and vitamins B as the analysis model to perform the new mechanism of pH-mediated for analysis switchable states cationic organic compounds: For analysis the benzidine and o-methylaniline in the environmental water samples by the acid-induced pH-mediated stacking with the recovery rate is between 94.3-101.7%; and for analysis vitamin B1 and nicotinamide in human urine samples by the basic-induced pH-mediated stacking with the recovery rate is between 83.4-106.3%.Chapter 3: In this work, we performed a new mechanism of t-ITP with the one-end closed capillary column to suppress EOF for analysis cationic organic compounds with switchable states. Closing one-end of the capillary column with the hydrogel can control the bulk liquid flow inside the capillary, which is an approach to suppress the suppressed EOF. Compared to the method of suppression the EOF at high acidity, it is much easier to realize the on-capillary enrichment of t-ITP. And compared to the traditional modified capillary method, experiments operation of hydrogel one-end closed capillary method to suppress EOF is simple. Frist, the ability of the hydrogel one-end closed capillary column to suppress the EOF was demonstrated by the electrophoretic migration time of the neutral marker DMSO in capillary zone electrophoresis(CZE) at different pH values. Then, we analyzed the melamine which as the analysis model by the new mechanism of t-ITP with one-end closed capillary column at higher pH values. The calibration curves of melamine showed good linear in the 0.01-10 mg/L. The method was successfully applied to the determination of melamine in four real milk samples with the recoveries in the range of 89.1-113.8 %.