DETERMINATION OF DISSOCIATION-CONSTANTS OF WEAK ACIDS BY DECONVOLUTION OF PROTON BINDING ISOTHERMS DERIVED FROM POTENTIOMETRIC DATA

Potentiometric titration of six carboxylic acid analytes were measured in aqueous and semiaqueous solvents to determine the effect of the so lvent composition on the dissociation constants of the acids. The anal ytes studied were monoprotic (formic acid, acetic acid), diprotic (mal eic and succinic acid) and triprotic (1, 2, 3,-propanetricarboxylic an d citric acid); the solvents were dioxane-water mixtures ranging in co mposition from 0 to 80% by volume dioxane. The methodology used to ass ess the acidity constants was deconvolution of the proton binding isot herm of each analyte in each of the solvents. The dissociation constan ts agreed with those reported in the literature for titration in water In the presence of the organic component, correlations relating the a cidity constants with properties of the media were also found. In part icular, affinity distributions derived from potentiometric titration d ata were used to assess the solvent media for resolving dissociation c onstants of weak acids and bases.