A technique is described for determining the electrochemical impedance of the repassivating interface. The method involves monitoring the response of the guillotined electrode to a single frequency perturbation continuously as a function of time. By measuring the process separately at many frequencies, full frequency spectra in time-resolved mode can be constructed for the repassivating interface. The time-resolved frequency response of aluminium guillotined in open circuit under immersion in aqueous solution is presented. Two RC time constants are identified for this system. One is attributed to the anodic process of oxide film growth, and the other to the cathodic process driving the anodic reaction. These are resolved to within 1 s after guillotining.