Analytical Sciences

Preconcentration and Determination of Mercury(II) at a Chemically Modified Electrode Containing 3-(2-Thioimidazolyl)propyl Silica Gel

Newton L. Dias FILHO,* Devaney R. do CARMO,* Laércio CAETANO,* and André H. ROSA**

*Departamento de Física e Química, Universidade Estadual Paulista (UNESP), Cx. Postal 31, CEP 15385-000, Ilha Solteira, SP Brazil
**Departamento de Engenharia Ambiental, Universidade Estadual Paulista (UNESP), CEP 18087-180, Sorocaba, SP Brazil

A mercury-sensitive chemically modified graphite paste electrode was constructed by incorporating modified silica gel into a conventional graphite paste electrode. The functional group attached to the (3-chloropropyl) silica gel surface was 2-mercaptoimidazole, giving a new product denoted by 3-(2-thioimidazolyl)propyl silica gel, which is able to complex mercury ions. Mercury was chemically adsorbed on the modified graphite paste electrode containing 3-(2-thioimidazolyl)propyl silica (TIPSG GPE) by immersion in a Hg(II) solution, and the resultant surface was characterized by cyclic and differential pulse anodic stripping voltammetry. One cathodic peak at 0.1 V and other anodic peak at 0.34 V were observed on scanning the potential from -0.1 to 0.8 V (0.01 M KNO₃; v = 2.0 mV s^-1 vs. Ag/AgCl). The anodic peak at 0.34 V show an excellent sensitivity for Hg(II) ions in the presence of several foreign ions. A calibration graph covering the concentration range from 0.02 to 2 mg L^-1 was obtained. The detection limit was estimated to be 5 µg L^-1. The precision for six determinations of 0.05 and 0.26 mg L^-1 Hg(II) was 3.0 and 2.5% (relative standard deviation), respectively. The method can be used to determine the concentration of mercury(II) in natural waters contaminated by this metal.

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