Generator–collector electroanalysis at tin-doped indium oxide–epoxy–tin-doped indium oxide junction electrodes

Generator–collector electroanalysis approaching the nanomolar level is demonstrated for the reduction of Ru(NH3)63+ in aqueous (NH4)2SO4 (saturated, as a naturally low-oxygen electrolyte medium) and at tin-doped indium oxide (ITO) electrodes. ITO–ITO double band and double plate geometries are compared. Cyclic voltammetric detection down into the sub-micromolar concentration level is readily achieved at co-planar ITO–ITO double plate junction electrodes with typically 4 μm inter-electrode gap, 5 mm length, and ca. 62 μm average inter-electrode trench depth. Trace oxygen (ca. 60 μM) is shown to enhance both generator and collector currents and the cathodic excess current |Igenerator| − |Icollector| is employed to estimate the bimolecular rate constant for Ru(NH3)62+ reacting with O2, k2 = 104 mol−1 dm3 s−1.