Determination of Mn(II) and Co(II) with Arsenazo III

Complex formation between Arsenazo III and Mn²⁺ and Co²⁺ at equilibrium has been investigated at pH 7.2, and the stoichiometry and stability of the complexes have been determined. The data indicate that Arsenazo III is suitable for determination of Mn²⁺ and Co²⁺ on the micromolar scale. The dissociation constants of the phosphate complexes of Mn²⁺ and Co²⁺ at pH 7.2 were estimated with Arsenazo III as 3.6 and 10 mM, respectively.