Development of a microfluidic system as basis for electrochromatography

In analytical separation technology there is a great demand for faster and more effective separation process. Miniaturization is a suitable technique for satisfying this demand because the reduction of the separation systems in size would give increased separation speed and higher efficiency. Capillary electrochromatography (CEC) is a separation technique, where the liquid flow is generated by an electric field. The main advantage of using an electric field instead of pressure to generate the flow is the flat profile of the electroosmotic flow (EOF). CEC is one of the best candidates to construct a novel, high throughput micro-analytical system. The aim of the present work was to develop the principles for applying the microfluidic approach to chromatographic separations. First of all the physical structure, the fluidic channel had to be constructed. Glass microstructuring and fusion bonding was used to create a closed channel structure with fluid reservoirs at the channels' end. Using chemistry developed for stationary phase synthesis for HPLC and CEC, the microchannels were transformed into chromatography columns. To be able to manipulate the liquid on the microchip, different connection and support units were developed. The developed microfluidic chip with a special connection and support unit was tested at high pressure and in an electric driven mode. The unit was made out of clean-room environment and able to operate under 150 bar pressure. In the next step, a nano-flow measurement and control unit was developed and constructed for the electric driven mode or for general application, where the liquid flows from an open reservoir. The novel, non-invasive fluid flow sensor can measure the flow in quasi real time giving an excellent basis for adaptive flow control in micro-fluidics. The flow-control system was modelled and its function was demonstrated. Finally, the developed micro-fluidic system was coupled with two different detection systems.