Pseudopolarographic Determination of Cd super(2+) Complexation in Freshwater

Pseudopolarography to detect Cd[2d+] complexes in samples collected at several locations along the Potomac River in June and September, 2004 was used. Irrespective of site and sampling time, no weak inorganic Cd[2d+] species were present. A Cd[2d+] chelate scale, generated from model ligands, was used to estimate the thermodynamic stability constants of the unknown complexes, which ranged from log K[THERM] = 21.5-32.0. This was partly attributed to highly stable Cd-sulfide species owing to the presence of acid volatile sulfide at concentrations greater than total dissolved Cd[2d+]. It was found that these electrochemically inert species may be multinuclear Cd-sulfide clusters and/or nanoparticles with K[THERM] values that exceed the detection window of pseudopolarography.