Abstract: Electrical coupling is usually considered as a side effect in the development of an electrochemical detection system for capillary electrophoresis. However, this effect can also be used for some electrochemical detection purposes. In this paper, an on-column dc contact conductivity detection using the coupling effect was presented, and the principle was elucidated. The characters of the method were demonstrated by chips of glass and polymer substrate with double-T detection cell. During the electrophoresis process, the electric field with a high strength was coupled to the sensing electrodes through the two detection channels, generating a potential difference that can be detected by the two electrodes in the outlet reservoirs. When a solute band passes a detection cell that was defined as a section of the separation channel, the potential drop will change and is proportional to the resistance of the solute in the cell. The level of coupled potential depends on solute conductivity, length of cell and electrical field strength, while the ratio of the potential over baseline depends only on the physical characters(conductivity or resistance) of the solution in the cell. The analysis results also show that this method responded not only to the charged species, but also to uncharged species. Electrical field strength above 450 V/cm could be applied with an homemade high input resistance signal transformer. Fast, reprodu-cible and sensitive detection was demonstrated for the separation of K⁺ and Na⁺ with a detection limit down to 5 μmol/L in 1 mmol/L Tris-HCl buffer and linear range over two orders of magnitude (10 μmol/L—2 mmol/L). This detection method can be used as a universal detector for capillary or chip electrophoresis system.

Key words: Chip electrophoresis, On-column conductivity detection, Electrical coupling, Universal detection method, Four-electrode configuration method