COMPOSITIONAL INFLUENCE ON THE PH OF REDUCED-MOISTURE SOLUTIONS

The pH of reduced-moisture systems is not the same as in hydrated systems. As aqueous phosphate buffer solutions become concentrated, the pH of the system decreases. The pH of citrate buffer solutions decreases, then increases as the concentration increases. Identical buffer solutions whose water activity is reduced by the addition of nonionic solutes indicate no correlation of pH with either the water activity reduction or the change in dielectric constant. The response of pH to added solutes appears to be dependent on the chemical nature of the solute and its interaction with water. This study also confirmed the limitations of several theoretical models of ionic activities.