The effect of ageing the electrode on the mass response was studied by two approaches, namely: i) ageing the Pt deposits on the Au/Q substrate and ii) ageing the Au/Q substrate and then examining the response of the Pt deposit on the aged Au/Q. Mass changes in the H-region are observed in both cases, which are attributed to an increase in water adsorption/desorption on the Pt surface, due to changes in the structure of the Pt deposit. These changes are not visible in CV curves