In-channel dual-electrode amperometric detection in electrophoretic chips with a palladium film decoupler

An electrophoretic microchip integrated with a Pd-film decoupler and a series-dual electrode was proven practical (200–800 V/cm) for routine amperometric detection. In fluidic systems, amperometric enhancement of parallel-opposed dual-electrode detection is due to redox cycling of analytes between the electrodes. We, however, found that the oxidation current of catecholamines was enhanced significantly (1.9–3.8 folds) by switching from the single electrode mode to dual-series mode. This novel finding was unexpected because the unidirectional flow characteristic of the microfluidic system should eliminate the possibility for analytes physically migrating back and forth between the upstream and downstream electrodes. We attribute the enhancement to turbulence generated by impinging of the flow onto the edge of the downstream electrode. The linear range, sensitivity, limit of detection (S/N=3) and number of theoretical plates for DA and CA are, respectively, 0.5–50 μM, 47 pA/μM, 0.25 μM, 7000 m−1, and 1.0–100 μM, 28 pA/μM, 0.49 μM, 15 000 m−1.