DETERMINATION OF MERCURY AT ELECTRODES MODIFIED WITH POLYMERIC FILMS OF [RU(V-BPY)3](2+) INCORPORATING AMINO-ACIDS

Electrodes modified with tryptophan, 6-amino-hexanoic acid, 4-aminobutyric acid, picolinic acid, and nicotinic acid as ligands (incorporated by ion exchange into a polycationic film of electropolymerized [Ru(v-bpy)3]2+) have been employed in the determination of mercury in solution. These ligands were chosen as representative of various types of amino acids, and the interest was to determine whether their affinity for mercury (which is related to mercury toxicity) is reflected in the analytical response. The redox response of the surface-immobilized mercury/ligand complex was used as the analytical signal. In all cases, calibration curves (log of the surface coverage-normalized redox response vs log [Hg]) exhibited an excellent correlation (r greater-than-or-equal-to 0.99) for mercury concentrations ranging from about 1 X 10(-8) to 1 X 10(-2) M and a relative standard deviation of 5-10%. More importantly, when the solution concentration of mercury was kept constant, we found a good correlation (r = 0.985) between the log of the normalized current (current/surface coverage) for the surface-immobilized mercury complex (employing the various ligands) and the log of the formation constants, indicating that the relative strength of coordination exhibited in solution was retained for the surface-immobilized ligands. The potential relevance of this work to speciation studies is discussed.