Radial Flow Microring Electrode:  Development and Characterization

The radial flow microring electrode (RFMRE), a new hydrodynamic ultramicroelectrode, is described. In the RFMRE, solution flows from a capillary nozzle, which is positioned very close to a planar substrate using micropositioners. The RFMRE can be operated in one of two configurations: either (a) with the ring electrode on the capillary or (b) with the ring electrode positioned in the plane of the substrate directly underneath the capillary. In both arrangements, as fluid leaves the capillary, it is forced into the nozzle/substrate gap and flows radially past the ring electrode. Under these conditions, the RFMRE is effectively analogous to a microband channel electrode. The RFMRE is shown to be characterized by well-defined, variable, and high mass-transfer rates under steady-state voltammetric conditions. Mass-transfer coefficients in excess of 2 cm s - 1 have been readily achieved with the RFMRE operating at relatively low volume flow rates (1.67 × 10 - 2 cm 3 s - 1 ). The device thus has considerable promise for electroanalysis and the study of fast electrode kinetics.