The use of titanium dioxide slurries or powders to enact the photocatalytic destruction of contaminants in water depends on its properties as a wide gap semiconductor. The charge transfer events at the water/semiconductor interface are strongly modified by the interaction of the titanium dioxide surface with solutes present in water, In this paper, we discuss the stability trend of the surface complexes formed by a series of organic anions (chemisorbed on TiO2). The surface interaction was studied by ATR-FTIR, and the spectra obtained at different complexant concentrations and pH values were used to derive Langmuir-type stability constants. It is shown that surface complexation can be described as the dissociative chemisorption of the neutral acid, with the creation of a zwitterionic surface species. There is a linear Gibbs energy relationship (LGER) between the stability of the surface complexes and the first acidity constant of the ligand, with slope of 1.8.