Speciation Studies of Iron (III) with (Poly)phosphonate Ligands: The Case of EDTMP (EthylenediamineTetramethylene Phosphonic Acid)

The complex formation equilibrium of ethylenediaminetetramethylenephosphonic acid (EDTMP, H₈L) with iron (III) has been studied potentiometrically at 25°C and an ionic strength of 0.2 M (NaCl). The successive protonation constants of ligand EDTMP and the complex formation constants were determined with the PSEQUAD program. Keeping in view the biological studies, the speciation in the system Fe (III)—EDTMP was calculated and drawn with the HySS computer program, and pFe values are compared.

Keywords:

• EDTMP
• Fe (III)
• HySS
• potentiometry
• PSEQUAD
• speciation

Notes

^a n represents the number of experimental observations in each titration.

^a Fitting (average difference between experimental and calculated titration curves expressed in cm³ of titrant) 0.0148; number of points 93; values in parenthesis are standard deviations in the last significant digit.

^b 25°C, I = 0.1 M (KNO₃).

^c 25°C, I = 0.1 M (KCl).

^d 25°C, I = 0.15 M (NaCl).

^a Fitting 0.0233; number of points 114; values in parenthesis are standard deviations in the last significant digit.

^b 25°C, I = 0.1 M (KNO₃).

^a pFe values were calculated at physiological pH (7.4).

^a Values from. ²²

^b pM values were calculated at physiological pH (7.4).