Microelectrode double potential step chronoamperometry is reported which allows the measurement of the diffusion coefficients of [Ru(NH3)(6)](3+) and [Ru(NH3)(6)](2+) in aqueous solutions containing various concentrations of the supporting electrolyte, KCl, KNO3 or K2SO4. In the case of K2SO4, ion-pairing of hexaammineruthenium cations is inferred where for KCl and KNO3 no such effects were noted. The triply charged ion was found to have a significantly lower diffusion coefficient than the doubly charged ion with a ratio of similar to 0.71 in the KCl and KNO3 media. (C) 2010 Elsevier B.V. All rights reserved.