Determination of Trace Quantities of Iron in Natural Substances with 3-(3'-Hydroxy-4'-Carboxyphenylazo)Pentadione-2,4 and Diantypyrylmethane and its Homologues

The complexation of iron(III) with 3-(3'-hydroxy-4-carboxyphenylazo)pentadione-2,4 (R) in the presence of diantipyrylmethane (DAM) and its homologues, diantipyrylpropylmethane (DAPM) and diantipyrylphenylmethane (DAPhM), is studied, and selective spectrophotometric procedures for determining its trace amounts in complex natural samples are developed. In an acidic medium, iron(III) with reagent R in the presence of diantipyrylmethane and its homologues forms mixed-ligand complexes Fe(III)-R-DAM, Fe(III)-R-DAPM and Fe(III)-R-DAPhM with a component ratio of 1 : 1 : 1, while bathochromic shifts and hyperchromic effects are observed in the absorption spectra, as well as a shift of the yield maximum to a more acidic medium compared to the homogeneous-ligand complex Fe(III)-R. The yield of the Fe(III)-R-DAM complex is maximum at pH 1.5–2.0, and of the Fe(III)-R-DAPM and Fe(III)-R-DAPhM complexes at pH 2.0–2.5. The influence of the concentration of reactants, temperature and time on the formation of the complexes is studied. The stability constants of the complexes are determined and it is found that in the presence of diantipyrylmethane and its homologues, the stability of the complexes increases by more than three orders of magnitude. Astakhov’s method is used to elucidate the chemistry of the formation of homogeneous and mixed-ligand iron(III) complexes. The calibration curves for determining iron(III) as homogeneous and mixed-ligand complexes are linear. A study of the effect of foreign ions on the determination of iron(III) revealed that the presence of diantipyrylmethane and its homologues significantly increases the selectivity of the reaction. The determination of iron(III) in the form of mixed-ligand complexes Fe(III)-R-DAM, Fe(III)-R-DAPM, and Fe(III)-R-DAPhM is not interfered with by more than 1000-fold amounts of Ca(II), Ba(II), Mg(II), Co(II), Ni(II), Zn(II), Mn(II), Cd(II), and other ions. The developed procedures are tested in the determination of trace amounts of iron in champignon mushrooms grown in the village of Zire, Baku, in cherries, and in water sampled from the Caspian Sea near the village of Turkan, Baku.