STANDARD PH VALUES FOR PHOSPHATE BUFFER REFERENCE SOLUTIONS IN ACETONITRILE-WATER MIXTURES UP TO 50-PERCENT (M/M)

Reference pH(PS) values for 0.025 mol/kg potassium dihydrogen phosphate + 0.025 mol/kg disodium hydrogen phosphate primary standard buffer solutions in 10, 30, 40 and 50% (m/m) acetonitrile-water mixtures at 298.15 K have been determined from reversible e.m.f. measurements of the cell Pt/Ag/AgCl/primary standard buffer + KCl in acetonitrile-water/glass electrode. The consistency of the results is confirmed by multilinear regression analysis of the pH(PS) values obtained for each solution composition. Considering the high number of possible acetonitrile-water mixtures, the methodology of linear solvation energy relationships (LSER) was applied and pH(PS) data have been correlated with the Kamlet-Taft solvatochromic parameters of the acetonitrile-water mixtures over the whole of the experimental range.