On-column conductivity detection in capillary-chip electrophoresis.

On-column conductivity detection in capillary-chip electrophoresis was achieved by actively coupling the high electric field with two sensing electrodes connected to the main capillary channel through two side detection channels. The principle of this concept was demonstrated by using a glass chip with a separation channel incorporating two double-Ts. One double-T was used for sample introduction, and the other for detection. The two electrophoresis electrodes apply the high voltage and provide the current, and the two sensing electrodes connected to the separation channel through the second double-T and probe a potential difference. This potential difference is directly related to the local resistance or the conductivity of the solution defined by the two side channels on the main separation channel. A detection limit of 15 microM (600 ppb or 900 fg) was achieved for potassium ion in a 2 mM Tris-HCl buffer (pH 8.7) with a linear range of 2 orders of magnitude without any stacking. The proposed detection method avoids integrating the sensing electrodes directly within the separation channel and prevents any direct contact of the electrodes with the sample. The baseline signal can also be used for online monitoring of the electric field strength and electroosmosis mobility characterization in the separation channel.