Electrochemical Study on the Stability of Phytate Complexes with Cu²⁺, Pb²⁺, Zn²⁺, and Ni²⁺: A Comparison of Different Techniques

Abstract

The formation constants of various M/Phy systems (M = Cu2+, Zn2+, Pb2+, Ni2+; Phy = Phytate) were determined in NaNO3 solutions at 0.1 ≤ I/mol·L−1 ≤ 1.0 and T = 298.15 K, by potentiometry and voltammetry. The formation constants of the Cu/Phy and Zn/Phy species, already determined, were reanalyzed together with new voltammetric and potentiometric experiments at low concentrations. A new potentiometric and voltammetric study was carried out on the Ni/Phy and Pb/Phy systems. For all of the investigated systems, the dependence on ionic strength was modeled by the Debye−Hückel and the specific interaction theory (SIT) approaches. The sequestering ability of phytate was evaluated toward the considered cations by calculating the pL50 values (i.e., the total ligand concentration necessary to bind 50 % of the cation present in trace) at different ionic strengths and pH. A complete set of “suggested” formation constants was provided. A comparison between the formation constants obtained for the Zn/Phy, Cu/Phy, and Pb/Phy systems reveals that the interactions of phytate with Zn2+, Cu2+, and Pb2+ are quite similar, while the Ni/Phy species showed a weaker complexation. For example, for the MH3Phy species, log K 3 = 7.81, 7.51, 7.10, and 5.97 for Zn2+, Cu2+, Pb2+, and Ni2+, respectively. The same trend is observed concerning the pL50. Their dependence on pH and ionic strength was modeled by two empirical equations.

The inorganic speciation of tin(II) in aqueous solution

“…The apparatus used in the potentiometric measurements has been widely described elsewhere (Cigala et al, 2010(Cigala et al, , 2012. The titrand solution consisted of different amounts of monosodium phosphate [1-20 mmol L À1 ], a suitable amount of HNO 3 [1-20 mmol L À1 ], and NaNO 3 to obtain the pre-established pH and ionic strength values (0.15 6 I/mol L À1 6 1.0).…”

“…The apparatus used in the voltammetric measurements has been described in detail elsewhere (Cigala et al, 2010;De Stefano et al, 2010). The voltammetric system was connected, by a remote box purchased from Metrohm (model 6.2148.010), to a Metrohm model 809 Titrando apparatus controlled by Metrohm TiAMO 1.2 software to perform automatic voltammetric titrations.…”

Voltammetric Investigation of Iron(III) Interactions with Phytate

“…To our knowledge, no fundamental electrochemical data regarding iron-phytate system on the mercury electrode has been published so far. In the past Witter et al [41] used static mercury electrode for 6 determination of stability and kinetic constants for some Fe(III) binding ligands (including phytate) in seawater by cathodic stripping voltammetry, and recently Cigala and coworkers [42] applied mercury electrode for determination of stability constants of some amalgam forming divalent metals with phytate via the anodic stripping titration technique. As shown in this work, HMDE is especially convenient for such study since it ensures highly reproducible electrode surface regeneration and enables investigation of the redox behavior of Fe(III)-phytate system also in acidic media in its whole range from Fe 3+ /Fe 2+ transition and up to the reduction of Fe 2+ to Fe metal.…”

Lead ion sensor with electrodes modified by imidazole-functionalized polyaniline

“…It is important to determine the lead content in both acidic and basic medium [32]. Hence lead sensing was repeated at pH 9.2±0.05 solutions with the modified GCE.…”