Integrated universal conductivity detection for chip electrophoresis

On-column conductivity detection in chip electrophoresis was achieved by active coupling the high electric field inherent to electro-osmosis with 2 sensing electrodes connected to the main capillary channel through 2 side detection channels forming a double-T. The method was demonstrated by using a glass chip with a separation channel incorporating 2 double-Ts, one of which was used for sample introduction, and the other for detection. Both numerical simulation and experiment results show that the potential difference between the 2 side detection channels is directly related to the conductivity of the solution passing through the channel. A detection limit of 15 mu M (600 ppb or 900 fg) was achieved for K+ in a 2 mM Tris-HCl buffer (pH 8.7) with a linear range of 2 orders of magnitude. The proposed detection method avoids micro-fabrication of sensing electrodes within the separation channel and prevents any direct contact of the electrodes with the solutes passing through the detection cell; meanwhile, conductivity detection and electrophoresis separation are seamlessly integrated in the same separation channel using the same high voltage power as a common activator.