Speciation of phytate ion in aqueous solution. Dimethyltin(IV) interactions in NaClaq at different ionic strengths

As the introduction of a systematic study on the sequestering ability of phytate (Phy) towards heavy metal and organometal cations, this paper describes the results of an investigation (at t = 25 °C by potentiometry, ISE-H+ glass electrode) of its interactions with dimethyltin(IV) cation [(CH3)2Sn2+, DMT] in NaCl aqueous solutions at different ionic strengths (0.1 ≤ I (mol L−1) ≤ 1), in the pH range 2.5 ≤ pH ≤ 8.5 and considering metal to ligand ratios 1:1 ≤ DMT:Phy ≤ 4:1. We observed the formation of 18 DMTiHjPhy(12−2i−j)− species: with i = 1 and 0 ≤ j ≤ 7; i = 2 and 0 ≤ j ≤ 5; i = 3 and 0 ≤ j ≤ 3. Their complex formation constant values are fairly dependent on ionic strength and this dependence was modeled by a Debye-Hückel type equation. The speciation of phytic acid and dimethyltin(IV) is also dependent on the metal to ligand ratio; the dependence of the stability of phytate-dimethyltin(IV) species on both the phytate protonation step and the number of cations bound to the ligand has been modeled and an empirical predictive relationship is also proposed. From the results obtained it emerged that phytate has very good sequestering ability towards (CH3)2Sn2+. Comparisons are made with other ligands, such as ethylenediamine-N,N,N′,N′-tetraacetic acid (EDTA) and phosphate.