Evaluation of protonation constants of binary complexes of diethylene triamine pentaacetic acid as ligands

Potentiometric studies have been carried out on H3ML and H2ML complexes where 'M' represents Mn(II), Zn(II), Pb(II), Hg(II), La(III), Ce(III), Pr(III) and Nd(III)and'L'represents diethylene triamine pentaacetic acid (DTPA) using Bjerrum-Calvin pH- titration technique. The Protonation constants of these complexes in solution (aqueous) have been determined at an ionic strength x = 0.1M KNO3 and temperatures 20°C and 40oC. The values of overall changes in free energy (?G), enthalpy (?H) and entropy (?S) accompanying complex formation have also been evaluated.