Determination of Nanomolar Mercury(II) Concentration by Anodic-Stripping Voltammetry at a Carbon Paste Electrode Modified with Functionalized Nanoporous Silica Gel

The aim of this study involves the determination of mercury ions at nanomolar level with the employment of the dipyridyl functionalized nanoporous silica gel-chemically modified carbon paste electrode (DPSG-CPE) by anodic stripping voltammetry. The experiments were conducted with a certain electrode composition of 25% paraffin oil, 60% high purity graphite powder and 15% DPSG as well as the usage of 0.20 M KNO3 as supporting medium. The reduction potential and time were set at, -200 mV and 450 s, respectively, and the scan rate at 100 mV s(-1) in the scan range of 200 to 500 mV. The analytical performance of the modified electrode was evaluated with respect to the carbon paste composition, the solution pH at the accumulation step, the preconcentration time, the mercury concentration, the possible interferences and other variables. On this modified electrode, the anodic stripping voltammetric mercury determination at nanomolar level concentrations was successfully attempted. The resulting electrode demonstrated linear response across a wide mercury(II) concentration range (20-100 nM) with a detection limit value of 8 nM, on the basis of a signal to noise ratio of 3. The precision for six determinations (n=6) of 40 and 75 nM mercury(II) was 5.0% and 2.8% (relative standard deviation), respectively. After studying the influence of the potential interfering ions, it was found that the proposed procedure was free from most interference. To testify the accuracy of this method, comparative determination of mercury(II) in wastewater samples by the proposed method and cold vapor AAS method were done and a sufficient sensitivity for the practical analysis of the environmental samples was attained.