Complexation of Iron (III) With Citrate and Tartarate Anions in Perturbed Aqueous Solutions Using Potentiometry and Difference UV/Vis. and IR Spectrophotometric Methods

Saeed Samavat1, Nader Gholami2 and Khodadad Nazari2,3*
1 Soil & Water Research Institute, Tehran/Iran
2 Chemistry & Petrochemical Division, Research Institute of Petroleum Industry, P. O. Box: 18745/4163, Tehran/Iran
  Tel: +98 21 44438526; Fax: +98 21 55932428
3 Institute of Biochemistrz & Biophysics, University of Tehran, Tehran/Iran

Complexation of iron (III) with citrate (Cit) and tartarate (Tar) anions was investigated in perturbed aqueous solutions using potentiometry, conductometry, UV/Vis. and infrared (FT-IR) spectrophotometric methods. Experiments were performed at 25 C in 0.1M sodium chloride solutions as the electrolyte. Stepwise equilibrium formation constants and the number of moles of ligand bound to Fe (III) were obtained from potentiometric titration data. Also UV/Vis. spectrophotometric results were used to determine the pH range of complex formation. Electrical conductivity of the Fe (III)/glucose (Glu) system showed that Glu is not bound to the iron. Potentiometric results could be used to estimate intrinsic association constants of the complexes. In the case of Fe (III)-Cit complex, two moles of Cit were bound to one mole of Fe (III) ion as determined by pH-titration and molar conductivity methods. Hill and Scatchard analysis of the Fe (III)-Cit. binding data indicated one set of binding sites, with positive cooperativity observed for the system. In the case of Fe-Tar, a complex in form of Fe (Tar)3 was formed over the pH range of 3 to 6. Hill and Scatchard analysis of the Fe (III)-Tar. data indicated that there are two unidentical and dependent sets of binding sites, and interaction between binding sites was of positive cooperativity type. FT-IR data of both complexes showed that complexation occurs by binding of carboxyl oxygen to the Fe (III) ion.

Keywords: Complexation, citrate, tartarate, pH-titration, Spectrophotometry, iron.