Design of detection electrode on contactless conductivity detector for capillary electrophoresis

The structure of detecting electrodes in a conductivity detector was studied to decrease the effect of the stray capacitance between the two electrodes on the detecting signal in capillary electrophoresis. The boundary element method was used to study the stray capacitance of two electrodes in contactless conductivity detection. Then, an electric field software was taken to simulate the electric field distribution of electrodes and to optimize the electrode structure with contactless conductivity. On the basis of simulated results, a novel sandwich electrode structure was proposed to decrease the direct capacitive coupling between the two electrodes. The effective length of the electrode is 200 μm, which decreases the stray capacitance between the two electrodes and overcomes its defect to be easy to breakdown. The experimental and simulation results indicate that the stray capacitance of proposed electrode structure is about 10^-5 F, which has been decreased about one order of magnitude as compared with those of conventional electrode structures. Moreover, two inorganic cations can be separated in 40 s at 220 V/cm separation voltage. In conclusion, the sandwich electrode structure is suitable for the contactless conductivity detection and improves detection sensitivity.