A silver disk electrode (diameter 0.2 mm) and composite silver electrode prepared from a mixture of silver, graphite powder and methacrylate resin (20 % Ag, 20 % graphite, 60 % methacrylate resin) are described. The electrodes prepared were used for the voltammetric determination of nitrate ions in samples of natural and wastewater (detection limit 7 mg L 71). The activation of the electrode surface before each measurement by a time-de®ned polarization ensures the reproducibility of the results of the voltammetric analysis. For the realization of such activation process the use of a computer-controlled instrument is necessary. For the electroanalytical measurement the advantages of the composite electrodes compared to solid silver electrodes includes simple preparation, low cost and electrochemical behavior typical to microelectrode arrays.

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The connection between the electrosorption and the voltammetric behavior of S 2 O 3 2¹ is demonstrated. The electrosorption of thiosulfate on mercury electrode in 0.1 M acetate buffer (pH 4.4), especially at potentials between 0.0 V and ¹0.35 V (vs. SCE) has been studied using an electrocapillary controlled convection drop-time technique. Strong adsorption of S 2 O 3 2¹ was confirmed exhibiting maximum changes of the surface tension of mercury around the potential E max ¼ ¹60 mV, where the adsorption coefficient b amounted to 105.2 m 3 mol ¹1 . The fitting of experimental results with the Frumkin adsorption isotherm was carried out and the resulting adsorption and interaction parameters were evaluated. The strong adsorptivity of S 2 O 3 2¹ was in agreement with marked increase of the voltammetric peak with accumulation time and it confirmed its combined faradaic electrosorption origin.