Assignment of pHs values of reference buffer solutions for standardization of potentiometric sensors in THF-water

Standard pH(S) values for five reference buffer solutions of the NIST series: KH(2)citrate, KH-phthalate, acetate, tetraborate and carbonate buffers in tetrahydrofuran-water, THF-water, mixtures containing 0, 10, 20, 30, 40, 50, 60 and 70% (w/w) THF at 298.15 K, have been determined using IUPAC standardization rules. The variation in the pH(S) values over the whole composition range of THF-water mixtures studied has been explained by preferential solvation effects, and quantified by application of the quasi-lattice quasi-chemical theory (QLQC). In order to identify the solvent features affecting the variation of pH(S) values with the percentage of THF, the pH(S) values obtained were subjected to factor analysis (FA) and were correlated with macroscopic and solvatochromic parameters, pi*, alpha, beta and E-T, of the solvent mixtures. The equations obtained permit the standardization of potentiometric sensors in THF-water mixtures and thus allow pH measurements in the usual way. The correct pH values measured permit the study of acid-base behaviour of substances in methodologies using THF-water media. (C) 1999 Elsevier Science Ltd. All rights reserved.