We propose to develop a new and generic, multi-probe technique to characterize the mass, and changes in mass, of material probed in a NR experiment. This methodology will be used to examine polyaniline films exposed to different solutions, providing for the first time, a complete, spatially resolved picture of the distribution of electrochemically driven electron, cation, anion and solvent populations. Control of the electrode potential will allow variation of PANI redox state with the fate of injected electrons being monitored using visible spectroscopy; the net ion transfer will be determined from the charge and partition into proton and anion contributions will be made using acoustic wave gravimetry. These probes will be combined to constrain and interpret NR derived, the spatial and time resolved density profiles that describe film composition at different stages in a redox cycle.