EQUILIBRIUM DIALYSIS-LIGAND EXCHANGE - A NOVEL METHOD FOR DETERMINING CONDITIONAL STABILITY-CONSTANTS OF RADIONUCLIDE-HUMIC ACID COMPLEXES

The equilibrium dialysis-ligand exchange technique (EDLE) is a combination of two classical techniques and is designed to measure the conditional stability constants of radionuclide-humic acid complexes over broad pH and ionic strength ranges. The use of a reference ligand hinders the hydrolysis of the radionuclide and enables the stability constant to be determined under neutral and alkaline conditions. By measuring the distribution of the radionuclide between the reference ligand and the humic acid, the conditional stability constant can be calculated. The technique was tested with Co-60(2+) and a commercial humic acid (HA) (Aldrich). It was possible to measure the conditional stability constants for the Co-HA complex for pH values between 5 and 10 in an ionic strength range between 0.02 and 0.2 M. The conditional stability constant increases non-linearly with increasing pH and decreases with increasing ionic strength.