Integrated capillary electrophoresis amperometric detection microchip with replaceable microdisk working electrode. II. Influence of channel cross-sectional area on the separation and detection of dopamine and catechol.

The interference of separation high voltage with the electrochemical detection is a major challenge to the microchip capillary electrophoresis-electrochemical detection systems with end-channel detection mode. Using dopamine and catechol as model analytes, the influences of channel cross-sectional area and channel-to-electrode distance on the high-voltage interference, accordingly on the separation and detection performances of the microchip capillary electrophoresis-electrochemical detection system were investigated. With the increase of the channel cross-sectional area from 312 through 450-615 microm2, the apparent half-wave potentials of hydrodynamic voltammetry for dopamine at the field strength of 288 V/cm shifted positively from 285 through 330-400 mV. By using a chip with the smallest channel cross-section (312 microm2 with top width of 37.3 microm and depth of 8.9 microm) the residual high-voltage field in the detection cell was small, so that detection was conducted at a channel-to-electrode distance of 20 microm to achieve better performances of separation and detection.