Equilibrium studies on interactions of rare earth ions with phytic acid

Abstract

The interaction between phytic acid and trivalent rare earth metal ions, viz., Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Gd³⁺, Tb³⁺, Dy³⁺ and HO³⁺ has been investigated potentiometrically at 25ᵒC. The proton-ligand stability constants (<em>pK</em><img src='http://www.niscair.res.in/jinfo/equation107.gif' border=0>) of phytic acid and the stability constants (log<em>K</em>) of metal complexes formed in aqueous medium (μ = 0.1 <em>M</em> NaClO₄) have been evaluated. The results indicate that eight protons of phytic acid are highly acidic, two are weakly acidic and two very weakly acidic, titrable in the <em>p</em>H ranges 1.2-4.9, 5.0-8.15 and 8.3-11.0 respectively. The stability of each phytic acid-lanthanide ion complex decreases with an increase in <em>p</em>H and follows the usual trend through the series.