Adsorption of L(+)-ascorbic acid on a mercury electrode in acid solution

The adsorption of L(+)-ascorbic acid on mercury in aqueous solutions of 10−2 M HClO4 has been determined from electrocapillary and capacity measurements. The maximum adsorption occurs at a charge of +2 μC cm−2. A Frumkin isotherm is obeyed. The standard Gibbs energy of adsorption is a quadratic function of the surface charge and the ΔGo value at zero charge is −24.9 kJ mol−1. The most probable model for the adsorption layer is that of two capacitors in series. The orientation of the organic molecule in the interface is discussed.