DETERMINATION OF COPPER AT ELECTRODES MODIFIED WITH LIGANDS OF VARYING COORDINATION STRENGTH - A PREAMBLE TO SPECIATION STUDIES

Electrodes modified with seven different ligands (incorporated by ion exchange Into a połycationic film of eiectropolymerized [Ru(v-bpy)3]2+) (v-bpy, 4-vinyl-4′-methyl-2,2′-bipyridyl)) whose formation constants for copper vary over a very broad range, have been employed in the determination of copper in solution in an effort to ascertain the utility of chemically modified electrodes to carry out speciation studies. The redox response of the surface Immobilized copper/ligand complex was used as the analytical signal. in all cases, calibration curves (log of the surface coverage-normalized redox response vs tog [Cu]) exhibited an excellent correlation (r ≥ 0.98) for copper concentrations ranging from 5 × 10−8 to 1 × 10−3 M. More Importantly, when the solution concentration of copper is kept constant, we find an excellent correlation between the log of the normalized current (current/surface coverage) for the surface Immobilized copper complex (employing the various ligands) and the log of the formation constants, indicating that the relative strength of coordination exhibited in solution is retained for the surface-immobilized ligands. The effects of having present other competing ligands including chloride, bromide, oxalate, ammonia and humic acid on the uptake of copper by the modified electrodes have also been studied. We find that the presence of competing ligands causes a diminution in the analytical signal due to copper incorporation and that the magnitude of this effect is dependent on the relative strength of coordination of the other competing ligands for copper Ions as well as on their concentration. The relevance of this work to speciation studies is discussed. © 1990, American Chemical Society. All rights reserved.