Square Wave Voltammetry Measurements of Low Concentrations of Nitrate Using Au/AgNPs Electrode in Chloride Solutions

The aim of this work is to highlight the potential of using a modified gold electrode with controlled quantity of silver nanoparticles as a working electrode to detect low concentrations of nitrate in chloride solutions. Optimal charge for silver deposition has been determined to obtain the highest signal for the nitrate reduction as the electrocatalytic properties of the bimetallic electrode were directly influenced by its composition. According to the Volcano plot obtained the charge chosen was −52 μC for a 3 mm diameter electrode, corresponding to 4.6×10 15 Ag atoms cm −2 . It has been shown that dioxygen did not participate to the nitrate reduction mechanism. In order to decrease the limit of quantification, square wave voltammetry was preferred to less sensitive cyclic voltammetry. Nitrate was quantified in chloride solutions in the concentration range found in the open ocean, i. e. 0.39–50 μmol L −1 with a good linear regression (R 2 =0.9969). The stability of the bimetallic Au−Ag systems has been evaluated and showed almost no difference on the signal recorded over a 26 days period which is suitable to consider an in situ sensor development for marine applications.