Concentration Polarization At Fused-Silica Capillary Membrane And Its Application In Capillary Chip Electrophoresis

With the development of microfluidics, the study on molecular transport behavior in micro-nano-scale become a new research field termed micro-nano-fluidics. The establishment and application of new micro-nano-fluidic system remain to be a hotspot. Concentration polarization effect at the micro-nano interface and its potential application in on-line preconcentration of micro-sample are receiving more and more concerns.In the first chapter of this paper, theoretical basis on electrical double-layer and related electrotransport phenomena were introduced with emphasis on sample pre-concentration issues in capillary chip electrophoresis system. The development and applications of concentration polarization occurring at the microchannel-nanochannel interfaces were summarized.In chapter II, an ion channel interface was established based on a capillary conductive membrane prepared by in situ HF etching. The concentration polarization effects on the interface were studied by microscope fluorescence imaging. It was found that in low ionic strength conditions, the membrane component exhibited obvious concentration polarization effect. The size of the ion channels in the membranes was estimated by fluorescent probes with different molecular radius. Preliminary results showed that the size of channels was between1.2nm and1.6nm scale. Additionally, it was noted that the monitoring electric field strength had a certain impact on the status of the conductive film.In chapter III, a capillary electrophoresis chip integrating with a fracture inlet and a conductive membrane was prepared, and concentration polarization effect under different conditions was investigated systematically, including reproducibility, electrolyte concentration, concentration time and voltage. Pre-concentration was found improved by applying appropriate tangential electric field. As estimated by fluorescent probe molecules, at least190times concentration was achieved. It was demonstrated that quartz capillary conductive membrane could concentrate not only macromolecules, but aslo small charged species by using the concentration polarization effect at the interface. It is expected that the capillary conductive membrane will find wide applications for online concentration of charged molecules.