A rigorous technique of analyzing impedance data for systems which have convective Warburg impedance elements in them has been developed. In particular, a rotating disk electrode system was analyzed, by solving the applicable transient convective diffusion equation numerically. The numerical solution was used to find nonlinear least squares parameters to fit an impedance data set, over the entire frequency range. In this manner the diffusion coefficient and other physical parameters of the system were determined without any assumption about electrode area, solution concentration, or kinetics. The shortcomings of the conventional techniques to evaluate physical parameters from impedance data have been overcome.