Resolution of coverage and field components in optical effects measured during specific adsorption has been demonstrated for the case of anionic adsorption on platinum electrodes. The coverage component was shown to be dominant when lower rates of potential scanning and larger solution concentrations of the adsorbing species were used. The field component could be easily resolved using periodical modulation of the potential at audio frequencies. For the resolution of the field component of δΔ/δ V, a version of off-null ellipsometry developed in this laboratory [10] allowed the direct and quantitative recording of fast changes in Δ, in the form of light intensity transients. The process of anionic adsorption on platinum constitutes a particularly interesting situation, since the signs of the coverage and field components of δΔ/δ V obtained at 546 nm are opposite. Thus, a straightforward example for the separability of these optical effects was provided. Field induced charge transfer from the adsorbed anions to the metallic substrate was examined as a possible explanation for the field effects measured. This process was simulated by the use of a simple model for the interface, in which an isotropic transparent (or slightly absorbing) film represented the adsorbed bromide layer. Charge transfer could be shown to result in a decrease of the effective thickness and refractive index of such a film, as well as an increase of its extinction coefficient. The field components of δΔ/δ V, 1/ R | δ R |/δ V and 1/ R ⊥ δ R ⊥/δ V, measured at 546 nm, could be simultaneously accounted for by combined changes in d, n film and K film with positive applied voltage, as predicted due to charge transfer enhancement.