Inverse chromatography was used to study the adsorption and desorption behavior of phenylalanine (pollutant model molecule) at the solid-liquid interface of a porous activated carbon with heterogeneous surface. The general isotherm form was obtained by the frontal analysis method in a wide range of phenylalanine concentrations. The method of frontal analysis by characteristic point was used to obtain the isotherms with a large number of points (about 3000) from single desorption chromatographic profiles. These isotherms were submitted to a mathematical treatment by the derivative isotherm summation analysis to obtain the insight into the energetic sites involved in phenylalanine-activated carbon interactions. The low-pressure quasi-equilibrium volumetric adsorption of argon was used to confirm the existence of the different energetic sites.