Ionization constants of pH reference materials in acetonitrile—water mixtures up to 70% (w/w)

Abstract

Ionization constants of pH reference materials in acetonitrile—water mixtures containing 30, 40, 50 and 70% (w/w) acetonitrile were obtained. The ionization constant values determined were: p K 1 and p K 2 for tartaric and phthalic acid; p K 1, p K 2 and p K 3 for citric acid and p K 1 for fabric and acetic acid. These values are essential to determine the standard reference value, pHs, for various standard reference buffer solutions. In the total composition range studied, p K values were linearly correlated with the mol fraction of acetonitrile and with the reciprocal of the dielectric constant of solvent mixtures. Considering the unlimited number of solvent mixtures, a multilinear regression procedure was applied to correlate p K values with % (w/w) and % (v/v) of acetonitrile, and the methodology of linear solvation energy relationships (LSERs) was used to relate p K data with solvatochromic parameters of acetonitrile—water mixtures.