STANDARD PH VALUES IN NONAQUEOUS MOBILE PHASES USED IN REVERSED-PHASE LIQUID-CHROMATOGRAPHY

Standard pH(s) values for three reference buffer solutions (0.05 mol kg-1 potassium dihydrogencitrate; 0.1 mol l-1 acetic acid +0.1 mol l-1 sodium acetate; 0.03043 mol kg-1 disodium hydrogenphosphate + 0.008695 mol kg-1 potassium dihydrogenphosphate) in 10, 30, 40, 50 and 70% (w/w) acetonitrile-water mixtures at 298.15 K were determined from e.m.f. measurements of the reversible cell Pt/Ag/AgCl/ standard buffer + KCl, in acetonitrile-water/glass electrode. In order to obtain pH(s) values in each of the unlimited number of possible acetonitrile-water mixtures, pH(s) values were correlated with mole fraction, % (w/w) and % (v/v) of acetonitrile in solvent mixtures and the methodology of linear solvation energy relationship, based on the Kamlet-Taft multiparametric scales, was applied and pH(s) data were correlated with pi*, alpha and beta solvatochromic parameters of the acetonitrile-water mixtures.