The reduction of dissolved oxygen has been studied over a wide conductivity range for use in steady or nonsteady hydrodynamic measurements. Mass transfer fluctuations can be analysed statistically to obtain the power spectra of hydrodynamic fluctuations. This requires a consideration of the proton reduction, which prevents diffusion from limiting the current. The transfer function for deducing the hydrodynamic spectra from mass transfer spectra includes not only transport effects but also kinetic effects which account for the finite rate of the reaction. The experimental study was performed using electrohydrodynamic (EHD) impedance.