Micro ion analysis

Due to the growing interest on micro total analytical system (μTAS), fast analysis of small amount samples with high throughout is highly desired. Conventional separation techniques, such as Liquid Chromatography, show a great potential for miniaturisation in order to perform fast separations at low cost. The miniaturisation of chromatography on microchip platform represents the objective of the thesis. The integration of sampling, separation and detection modulated in the micro scale is the main focus of the thesis project. A capillary ion chromatography system has been developed and characterised. In order to adapt to the small volumes and fluid flow rates, new designs for injection and detection were evaluated. Compared to the conventional ion chromatography, the ion separation with similar efficiency (in terms of resolution and retention time) has been obtained. Pressure driven flow injection methods have been developed on microchips to ensure nanoliter volume injection without sample component discrimination. Two different methods ware developed: pinch and push/pull injection. In both cases, the diffusion of sample solution during injection focusing is controlled leading to welldefined injection volumes. Furthermore, fundamental studies of the pinch injection method have also been carried out by numerical simulations. The optimal flow velocity then has been determined for a flow pinch injection. The effects of the probe position, pullback velocity and the injection channel width have also been also considered. Capillary electrophoresis in microchips has also been studied and some selective functions to improve the separation efficiency are proposed. Self-assembled monolayer technique for microchannel surface modification was also investigated to develop new chromatographic stationary phases. This application has enbled a fast ion separation in a very short channel. In another experiment, the use of pseudo-stationary phase in the running buffer was also studied. Finally, the concept of a new detection method based on conductivity measurement is presented and validated by experiments and numerical simulations. This detection is typically used for electrophoretic separation. No decoupling between the separation field and the detection circuit is required.