The Use of thin mercury film electrodes modified with polymers for the voltammetric analysis of trace metals in biological and environmental samples

The objective of this study is to develop polymer coated thin mercury film electrodes that will show selectivity towards one or more of the Cu, Pb and Cd ions, and to utilize these electrodes, without any sample pretreatment except dilution and pH adjustment, for the voltammetric stripping determination of these metallic species in biological and environmental samples. Thin mercury films (TMFE) were grown by time-controlled bulk electrolysis on voltammetric glassy carbon electrodes at a constant potential of -0.7 V vs. Ag/AgCl in a KNO3 supporting electrolyte solution (pH=l) containing 5xlO"5M Hg(N03>2. Polyindoline coated glassy carbon electrodes (ICGCE) were prepared by charge- controlled electrolysis at a constant potential of +05 V vs. Ag/AgCl in a 0.1 M a KNO3 supporting electrolyte solution (pH=5.58) containing 20 mM indoline. Polyindoline coated mercury film electrodes (ICMFE) were prepared by growing mercury films on ICGCE's in a medium containing lxlO"4 M Hg(NOs)2. Polyindoline electrodes showed no voltammetric stripping signal for Cu, Pb and Cd ions. Responses of TMFE and ICMFE were studied employing synthetic solutions containing the three ions and the parameters affecting the differential pulse stripping voltammetric (DPSV) response such as type of supporting electrolyte, thickness of mercury film, thickness of polymer film and deposition time were systematically investigated and optimal analysis conditions were determined. The optimized electrodes were then used for the analysis of Cu, Pb and Cd in urine samples, either decomposed by hot HNO3 or untreated except for dilution and pH adjustment. DPSV responses of these three ions obtained in untreated urine samples employing ICMFE were then compared with those obtained by using TMFE, and it was seen that polymer coated mercury film electrodes at concentrations as high as 100-150 ppb showed no response for Cd, and the electrode could be classified as negative- selective for the said ion. In decomposed samples situation was different, a response for Cd, although small, was seen. f * Ilk KEY WORDS: mercury film electrode, modified electrode, copper, lead, cadmium^ differential pulse anodic stripping voltammetry.