Speciation of phytate ion in aqueous solution. Characterisation of Ca-phytate sparingly soluble species
2004
Crea, Francesco | Crea, Pasquale | De Robertis, Alessandro | Sammartano, Silvio
The formation of sparingly soluble Ca²⁺-phytate (Phy) species was studied using several techniques (potentiometry, calorimetry, thermoanalysis, ICP, SEM). Species with empirical formula CaₓH(₁₂_₂ₓ)Phy, (6 ≤ x ≤ 4.5) were formed in experiments performed at pH = 5.0, 7.5 and 10.5; at pH = 10.5 and in excess of Na+ the species Ca₅Na₂Phy was also found. Solubilities (s = 1.0 x 10⁻⁹and 1.1 x 10⁻¹⁰mol L⁻¹ for the species Ca₆Phy and Ca₅Na₂Phy respectively, at l = 0 mol L⁻¹), thermogravimetric profiles (dehydratation, monohydrogen-phosphate and final pyrophosphate formation), and formation enthalpies (ΔΗ = 7.6 ± 1 and 3.7 ± 0.8 kJ mol⁻¹for the equilibria 6Ca²⁺ + H₃L⁹⁻ = Ca₆L⁰ + 3 H⁺ and 5Ca²⁺ + 2Na⁺ + H₃L⁹⁻ = Ca₅Na₂L⁰ + 3 H⁺, respectively), were obtained.
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