Electrochemical detection based on redox cycling using interdigitated microarray electrodes at μL/min flow rates

The influence of convection on the degree of redox cycling at interdigitated microarray electrodes in a flow system was investigated in the end column detection mode for flow rates below 20 mu L/min. It was found that the degree of redox cycling increased with decreasing flow rates and values of 2.9 and 2.2 were obtained for a flow rate of 2 and 20 mu L/min, respectively using photolithographically fabricated interdigitated arrays consisting of 140 microbands separated by 6 mu m. The obtained degrees of redox cycling were lower than the value of 4.4 obtained in a stationary solution in the batch mode as a result of a decreased collection efficiency between adjacent microbands and a relatively low conversion efficiency at each microband in the presence of the flow It is shown that a collection efficiency of more than 90 % is needed to produce an order of magnitude increase in the current due to redox cycling in a stationary solution. When using a microarray electrode consisting of 280 microbands in a thin layer flow cell, a conversion efficiency of close to 100 % could be obtained at flow rates below 1 mu L/min. In the latter case, a significantly larger flow rate dependence of the current was found compared to that for a single microband electrode.