| The principle of Donnan membrane equilibrium is used to quantitatively separate the cationic forms of the trace metals cooper, zinc, and cadmium from their complexes by the selective diffusion of the cations across a strong acid cation exchange membrane (SACEM) without disturbing the solution equilibria. The concentrations of the cations are then determined by electrothermal atomization atomic absorption spectrophotometry (GFAA). An 0.01M alkali earth metal nitrate solution containing the trace metals (the donor solution) is circulated through one-half of an exchange cell. The donor solution is separated from an acceptor solution (0.200 ml of 0.01M Sr(NO(,3))(,2)) by the SACEM. Equilibrium of cations with a +2 charge is obtained in 60 minutes. Cations with a +1 charge diffuse at a much slower rate, and their concentration in the acceptor solution is 10% of the donor solution concentration after 60 minutes. The diffusion of negatively charged complexes is not detected.; The diffusion process is shown to conform to current theories of trace cation diffusion across cation exchange membranes. The diffusion-time profiles for trace cation diffusion calculated from equilibrium and non-steady state data describe the experimentally determined profiles.; Detection limits for the method are determined by the GFAA analysis, and are 10('-8)M for copper and 10('-9)M for zinc and cadmium. The method is not subject to the interferences that prevent electrochemical techniques from being applied to natural systems. The procedure is used to determine the cation activities of copper, zinc, and cadmium in 0.01M Sr(NO(,3))(,2) extracts of soils and sewage sludge. The result is an analytical procedure that is specific and sensitive to cationic forms of trace metals in soil extracts and natural waters. |
