Transmetallation of Gd-DTPA by Fe3+, Cu2+ and Zn2+ in water: batch experiments and coagulation-flocculation simulations.

The study investigates the stability of gadolinium-DTPA complex in presence of competing metallic ions, Fe(3+), Cu(2+) and Zn(2+) using batch experiments and coagulation-flocculation simulations. High performance liquid chromatography with fluorescence detection was used for simultaneous analysis of chelate gadolinium (Gd-DTPA) and free Gd(III) ion in water. It was shown that Cu(2+) has a strong affinity for DTPA and could lead to a complete release of Gd(3+). Fe(3+) appeared also to compete strongly with Gd(3+) for DTPA binding since up to 80% of Gd-complex was dissociated under iron excess condition. Finally, zinc had a lower influence on Gd speciation: only 15% of Gd(3+) was released with addition of a 5-fold excess of Zn(2+). During coagulation-flocculation simulation, Fe(3+) was able to displace about 27% of Gd-DTPA, and no adsorption was observed onto flocs.