Metal Displacement at the Zinc-Diethyldithiocarbamate-Modified Carbon Paste Electrode for the Selective Preconcentration and Stripping Analysis of Mercury(II)

Abstract

A carbon paste electrode modified with zinc diethyldithiocarbamate was used for the selective accumulation of mercury(II) based on the metal displacement principle. Selectivity was achieved by exploiting differences in conditional extraction constants. After accumulation, medium exchange was performed. The accumulated HgII was then reduced to metallic mercury in 0.10 M KSCN - 0.010 M HClO4 followed by differential pulse anodic stripping voltammetry in the same medium. Factors affecting the accumulation, reduction and stripping steps were systematically investigated. An optimized procedure was then developed for the determination of HgII. Under optimum conditions, a detection limit of 8.0 × 10-10 M Hg(II) was obtained for a 15 min accumulation. For 6 determinations each of 1.00 × 10-7 M and 5.00 × 10-8 M HgII, relative standard deviations were 1.5% and 3.3%, respectively. The presence of selected metal ions and other organic and inorganic substances gave no observable interferences. However, interferences were observed when 1.00 × 10-3 M NH4SCN, Na2EDTA and NH4Br were present. These interferences can be readily overcome by digesting the samples with oxidizing agents. The developed method was applied to the analysis of mercury in a U.S. Environmental Protection Agency water quality control sample and also in a human urine sample.