Speciation of phytate ion in aqueous solution. Protonation in CsClaq at different ionic strengths and mixing effects in LiClaq + CsClaq

This paper reports the results of an investigation (at t = 25 °C by potentiometry, ISE-H+ glass electrode) of phytate acid-base properties both in simple CsClaq solutions at different ionic strengths (0.1 ≤ I/mol L− 1 ≤ 1.75) and in LiClaq−CsClaq mixtures at I = 1.28 mol L− 1 and different Li+/Cs+ mole fractions [y = CLi/(CLi + CCs)]. These last measurements allowed us to evaluate the mixing effects on phytate protonation, and the deviation from the ideal mixing (Young rule) has been interpreted by means of a Δ parameter that can be associated to the free energy of mixing (ΔGmix) or, alternatively, in terms of formation of simple and mixed metal complexes. Dependence of protonation constants on ionic strength in simple CsClaq solutions has been taken into account by a Debye-Hückel type equation. Complex formation constants for CsjHiPhy(12 − i − j)− species at different ionic strengths have been calculated too, and comparisons have been made with phytate acid base behavior in other alkali metal chloride aqueous media.