Determination of Protonation Constants for 2-Hydroxy-1-(2-Hydroxy-4-Sulpho-1-Naphthylazo)-3-Naphthoic Acid

Abstract

Chemical speciation modelling in combination with potentiometric titration method was used to determine the protonation constants for 2-hydroxy-1-(2-hydroxy-4-sulpho-1-naphthylazo)-3-naphthoic acid, the Patton and Reeder’s reagent, at 25° C in three ionic strengths of 0.1 mol dm-3, 0.01 mol dm-3 and 0.001 mol dm-3 NaNO3. Potentiometric titrations were performed and pH, titrant volume, temperature and free and total proton concentrations at each titration point were measured. Constants were determined for three of the four protonated sites and the forth one being a very low value as this site is always in the ionic form and is readily ionized in aqueous solutions