Assignment of pH(s) 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 serie s: KH(2)citrate, KH-phthalate, acetate, tetraborate and carbonate buffers i n 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 stan dardization rules. The variation in the pH(S) values over the whole composi tion range of THF-water mixtures studied has been explained by preferential solvation effects, and quantified by application of the quasi-lattice quas i-chemical theory (QLQC). In order to identify the solvent features affecti ng the variation of pH(S) values with the percentage of THF, the pH(S) valu es obtained were subjected to factor analysis (FA) and were correlated with macroscopic and solvatochromic parameters, pi*, alpha, beta and E-T, of th e solvent mixtures. The equations obtained permit the standardization of po tentiometric sensors in THF-water mixtures and thus allow pH measurements i n the usual way. The correct pH values measured permit the study of acid-ba se behaviour of substances in methodologies using THF-water media. (C) 1999 Elsevier Science Ltd. All rights reserved.