Full Paper Nafion Coated Silver Amalgam Electrode for Determination of Trace Metals by Anodic Stripping Voltammetry Kristina Strasunske, a Øyvind Mikkelsen, a * Gabriel Billon b a Norwegian University of Science and Technology, Department of Chemistry, N-7491 Trondheim, Norway b University of Lille I, Laboratory Ge ´ osyste `mes (UMR CNRS 8157), 59655 Villeneuve dAscq, France *e-mail: oyvind.mikkelsen@chem.ntnu.no Received: September 15, 2009 Accepted: November 21, 2009 Abstract This paper describes characterization and application of Nafion coated solid silver amalgam electrodes to prevent surface fouling of surfactants in determination of trace metals by differential pulse anodic stripping voltammetry (DPASV). Polymer films of different thickness were tested using Nafion solutions in the range 0.25%– 1%. Optimum thickness was archived using a 0.5% Nafion solution, resulting in both increased response and stability over time compared to uncoated electrodes. The influence of model surface active macromolecules was studied using triton X- 100, sodium dodecyl sulfate, dodecyl pyridinium chloride and bovine serum albumin as representatives for surfactants. The resistance to surfactants makes the studied Nafion coated solid silver amalgam electrodes an interesting alternative for practical use in environmental monitoring. Keywords: Stripping voltammetry, Solid electrodes, Nafion modified electrodes, Trace metals, Surfactants, Amalgams DOI: 10.1002/elan.200900462 1. Introduction Differential pulse anodic stripping voltammetry (DPASV) is a highly sensitive electroanalytical technique for measur- ing trace metals and one of few techniques suitable for online environmental monitoring. However, a problem in direct determination of trace metals by voltammetry in real samples is the possible presence of surface active com- pounds [1 – 2]. Actually, this is one of the most serious interferences in practical application of DPASV because adsorption of surface active compounds on the electrode surface causes fouling and may result in both loss of sensitivity, broadening, shifts and undefined peak signals [3 – 6]. In voltammetric systems made for long time surveil- lance, like in field stations which are not maintained on a regular basis, surface fouling is an important factor to take into account. This is especially important in sample matrices containing significant amounts of surface active compounds. Modification of the electrode surface by e.g. applying a protective polymer film layer might however partly prevent adsorption of surface active compounds. A polymer film will mechanically block the surfactant species from reaching the electrode surface, while small metal cations can diffuse through the film and reach the electrode surface. Several compounds have been tested for this purpose. Agarose gel has been widely used in the purpose of in situ trace metal monitoring [7]. However, one of the main problems with agarose is the thickness of the gel layer, which is in the order of several hundreds of micrometers and its lack of adherence on electrode surface. Consequently, before measurement a period is needed permitting the species to diffuse in the gel. In addition, as the convection cannot be established near the surface of the electrode, agarose is mainly reserved to microelectrodes. Cellulose acetate membrane has also been used and reported to obtain good resistance towards organic interferences [8], but the electrode modification procedure is complicated and therefore inconvenient for practical use. Nafion film is a widely and easy to use electrode modifier with good stability. A film, formed by Nafion on the electrode surface is electro inactive, chemically inert and hydrophilic. It has exceptional properties of super selectiv- ity and facile cation transport. Moreover, it can pre- concentrate a wide variety of cations while rejecting anionic interferences. These properties are due to the microstruc- ture of Nafion that looks like segregated domains of fluorocarbon and clusters of hydrated sulfonate sites where cations can travel across the membrane through intercon- nected hydrated domains [9, 10]. Nafion coatings to prevent fouling has been studied in combination with several different types of electrodes like carbon and glassy carbon electrodes modified with or without bismuth film [6, 11 – 18], and mercury film electrodes [19 – 27] for practical applica- tions in tap water and white wine [13, 17], plant extracts [15], vegetable [16], body fluids [19, 20], wastewater [23, 25], estuarine water [27]. In most of these contributions an increased electrode sensitivity and better resistance to surface active compounds [11 – 17, 19 – 27] is reported. Solid silver amalgam electrode [28 – 30] retain many desirable features of mercury (e.g., high hydrogen over- potentials), and has been proven to be an interesting Full Paper Electroanalysis 2010, 22, No. 5, 501 – 507  2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 501