The three acid dissociation constants (pK(a)s) of the 8-hydroxyquinoline-5-sulfonic acid were computed using a computational protocol based on Density Functional Theory. A hybrid exchange correlation functional was applied and bulk solvent effects were treated within the framework of the Polarizable Continuum Model. Direct solute-solvent interactions were taken into account adding explicit water molecules. The computed pKas are in line with the experimental data and allow better de. ning the first pKa, confirmed to be negative. From the calculated pKas, 'ab initio' distribution diagrams of the relative concentration of the different species in solution as a function of pH were drawn. (C) 2009 Elsevier B. V. All rights reserved.