Coulometry: A Fine Procedure to Determinate Acidity Constants of Slightly Soluble Acids

The flowing of constant direct current allows planning a coulometric method to determine solubility and acidity constants of slightly soluble acids. Coulometry combined with electromotive force (emf) measurements is applied to obtain such parameters for eight bile acids, simple and conjugated with glycine in solutions in real equilibrium and without formation of micellar aggregates. Results, obtained in different ionic media, (1.00, 0.50, and 0.15) mol.dm(-3) NaCl (i.e., in physiologic conditions), are compared with previous data, extrapolated from mixed solvents or obtained in oversaturated solutions. The proposed method is not difficult to perform, and it can be applied to other slightly soluble acids or in very low concentrations, without a complicated elaboration of the experimental data.