High-voltage capacitively coupled contactless conductivity detection for conventional and microchip capillary electrophoresis

This thesis focuses on the optimisation of capacitively coupled contactless conductivity detection for capillary and microchip electrophoresis and its applications in analytical chemistry. First, the effect of high excitation voltages and operation frequencies on the capacitively coupled contactless conductivity detector cell for conventional capillary electrophoresis is evaluated. The detector electrodes comprised two steel tubes cut from hypodermic needles, through which the capillaries were inserted. It is demonstrated that increasing excitation voltages from 25 V pp, to 250 Vpp improves the detection limits by a factor of 10. The high actuator voltage approach was also investigated for contactless conductivity detection on a glass-microchip device with ancm long channel. The detector electrodes formed part of the microchip and were placed on the microchip directly above the microchannel. In a separate project the simplification of on-microchip contactless conductivity detection was accomplished. This was achieved by integrating the detector electrodes on to a chip-holder specifically designed for this purpose. Thus the electrodes were a part of the holder, an improvement of the previous arrangement whereby the detector electrodes were situated on the microdevice. Finally the applications and advantages of the optimised high-voltage capacitively coupled contactless conductivity detection for inorganic and organic analysis were demonstrated. The separation and detection of 14 metal ions was accomplished in less than six minutes. The compatibility of this detector with non-UV transparent, polymer capillaries has been demonstrated. The detection of native amino acids has been evaluated. Part of the work was dedicated to the on-chip analysis of various classes of organic ions. The two immunoproteins human immunoglobulin M (IgM) and immunoglobulin G (IgG), were analysed in their unlabelled state on both capillary and lab-on-chip platforms. All species involved in an immunological interaction between IgM and IgG could be detected. A method for the analysis of selected basic pharmaceutical drug substances was developed. Detection limits comparable to those supplied by direct UV detection were obtained. Main component assays of selected pharmaceutical preparations have been demonstrated.