For the independent and simultaneous characterization of electrochemical processes, we employ surface plasmon resonance (SPR) detection together with standard electrochemical methods. As a first test system we studied sulfate adsorption on Au(111). After careful calibration of the SPR signal we obtained submonolayer sensitivity on a millisecond time scale. The experimental data are simulated within the framework of a layer stack model of the optical interface. The sulfate adsorbate is simply described, employing the optical properties of sulfuric acid. The obtained potential dependent sulfate coverage is in reasonable agreement with independent results as presented in the literature.