The effect of the tetraalkylammonium salts on the protonation thermodynamics of the phytate anion

In this paper new potentiometric titrations were performed on the protonation of phytate at different temperatures 278.15 K ≤ T/K ≤ 323.15, ionic strengths and in different ionic media, namely (CH3)4NCl (0.1 ≤ I/mol dm−3 ≤ 3.0) and (C2H5)4NI (0.1 ≤ I/mol dm−3 ≤ 1.2). A complete set of phytate protonation constants, with general formula HiPhy (with 1 ≤ i ≤ 8), was proposed.The dependence of protonation constants on ionic strength was calculated by using three different approaches: (i) Debye–Hückel (DH) type equation, (ii) SIT (specific ion interaction theory) approach and (iii) the formation of weak complexes. It is important to underline that the whole study was done using K2H10Phy as phytate source, because the presence of an interacting cation, such as K+, affects significantly the values of the apparent protonation constants. Different K+ concentrations in the considered range (0.001 ≤ cK/mol dm−3 ≤ 0.01) cause a difference of ±0.05 in the protonation data.Furthermore, the weak complexes between phytate and (CH3)4N+ cation were determined at different ionic strengths, and different protonated species, having general formula HiMjPhy [0 ≤ i ≤ 6 and 1 ≤ j  ≤ 5] were reported.This paper represents an improvement in the understanding of the solution behavior of phytic acid in a wide range of ionic strengths and in different ionic media.