| Abstract
| - Changes in pH induced by the addition of electrolytes to buffers, polyelectrolytes (a polycarboxy polymethyleneand a polyethyleneimine), and proteins (casein, whey, and lysozyme) solutions are explored systematically.The two buffer systems are triethanolamine/triethanolammonium chloride and citric acid/sodium citrate. Theseare chosen because of the similarity of their acid−base equilibria with those of amino acids predominant inmost proteins, that is, amino acids that include carboxylate or ammonium groups in their structures. The pHof triethanolamine and of citrate buffers respectively increases and decreases when salt is added. At lowelectrolyte concentrations (<0.15 mol/kg), the phenomenon is well accounted for by standard electrostatictheories. pH values at higher salt concentrations are not reliable when measured with a commercial glasselectrode without cross-checking by a standard hydrogen electrode. The changes of the pH values ofpolyelectrolyte and protein solutions with added salts turn out to be remarkably similar to the salt induced pHchanges in the buffer solutions. It is even possible to qualitatively predict these changes in protein solutionssimply from the primary protein structure. At least in the systems considered here, the specific ion effects onpH seem to correlate with the bulk activity coefficients of the added electrolytes, at least at moderate saltconcentrations.
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