Graphite electrodes modified with gold-polymer compound for mercury determination by stripping voltammetry

The method of stripping voltammetry has high sensitivity, accuracy and low limits of detection. But metrological characteristics of analysis methods are mostly determined by the type of electrode systems, which are used in them. One of the main trends of modern electrochemical analysis is modification of electrodes with different components which could increase sensitivity of detection and reduce interference. The usage of polymers composition is a perspective direction in creating of new electrodes. This composition consists of polymer matrix with a modifier, which mediates electrode processes. Thus, in mercury analysis chemists often use gold which decreases the energy of a new phase generation and helps to decrease the limit of detection. We offer to form gold nanoparticles in polymer film, which is applied to the surface of graphite substrate. Polymer stabilizes the system and allows uniform distribution of particles in polymer matrix. Composite materials based on acrylic copolymer were investigated in current work. These polymers contain carboxyl groups of methacrylic acid, which provide ion transport, and methyl methacrylate, acting as a builder. During electrolysis of AuCl , ions that are embedded in a polymer matrix are reduced to elemental gold, forming metallic gold clusters on the surface of graphite. These clusters are isolated one from another by polymer composition. In order to increase electrical conductivity of composition and to improve ion transport we suggested to form gold-polymer film with polyethylene glycol addition. When this electrode is immersed in an aqueous solution, polyethylene glycol is washed away, resulting in formation of pores through which ions diffuse defined by the centers of metallic gold. Influence of the polymer solution composition and method of graphite electrode modification on mercury recovery were estimated. Optimal ratio for the formation of Au-polymer electrode ''methacrylate: methacrylic acid : polyethylene glycol'' is equal to 6:1:2, the gold content is 0.025 mM/kg of the polymer. The ratio of the copolymer (ul) to the electrode surface (mm ) is 2:1, potential of pre-electrolysis is -0.7 V. Comparative surface analysis of Au-carbon polymer electrode (Au-CPE) and Au-carbon electrode (Au-CE) were conducted using by electron microscopy. It can be concluded that Au-carbon polymer electrode (Au-CPE) provides equal to Au-CE sensitivity in mercury detection at ten times less number of active sites on the surface. Tests of the developed electrode were carried out on the samples of natural water, biological objects and food. Analysis results are in good agreement with those obtained by atomic absorption spectrophotometry (AAS).

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