Capillary electrophoresis with on-chip four-electrode capacitively coupledconductivity detection for application in bioanalysis

Microchip capillary electrophoresis (CE) with integrated four-electrode cap acitively coupled conductivity detection is presented. Conductivity detecti on is a universal detection technique that is relatively independent on the detection pathlength and, especially important for chip-based analysis, is compatible with miniaturization and on-chip integration. The glass microch ip structure consists of a 6 cm etched channel (20 mum x 70 mum cross secti on) with silicon nitride covered walls. In the channel, a 30 nm thick silic on carbide layer covers the electrodes to enable capacitive coupling with t he liquid inside the channel as well as to prevent interference of the appl ied separation field. The detector response was found to be linear over the concentration range from 20 mum up to 2 mM. Detection limits were at the l ow tm level. Separation of two short peptides with a p/ of respectively 5.3 8 and 4.87 at the 1 mM level demonstrates the applicability for biochemical analysis. At a relatively low separation field strength (50V/cm) plate num bers in the order of 3500 were achieved. Results obtained with the microdev ice compared well with those obtained in a bench scale CE instrument using UV detection under similar conditions.