Abstract Generator–collector electroanalysis approaching the nanomolar level is demonstrated for the reduction of Ru(NH 3 ) 6 3+ in aqueous (NH 4 ) 2 SO 4 (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 | I generator | − | I collector | is employed to estimate the bimolecular rate constant for Ru(NH 3 ) 6 2+ reacting with O 2 , k 2 = 10 4 mol −1 dm 3 s −1 .