Electroanalysis with chemically modified electrodes

The feasibility of using electrodes with functionalized polymer films for performing electroanalysis in solution is demonstrated. The proposed approach not only takes the advantages of the favorable aspects of chemically modified electrodes (e.g. sensitivity) but also provides many synthetic variations (and therefore) as well as ways to detect and overcome matrix and saturation effects. The method is based on the use of copolymer films that incorporate both an electroactive center (used for inducing precipitation of the polymer on the electrode) and a coordinating site chosen on the basis of the species. Even though the method is presented in the context of electroanalysis of metal ions in solution, this approach could be extended to be determination of organic functionalities through the appropriate choice of reagents.

Today there is a great need for the development of analytical methods for the selective and quantitative determination of metal ions and organic contaminants at trace level, particularly, in the light of new challenges posed by environmental samples. One field that offers great potential in this respect is that comprised by chemically modified electrodes. Chemically modified electrodes are very suitable for electroanalytical applications since they offer high sensitivity. There have been some reports on the use of chemically modified electrodes for electroanalysis. One of the first examples of the analytical utility of these modified interfaces was represented by Lane and Hubbard. In their work they complexed Fe (III) ions from the aqueous solution using a salicylate ligand that was chemisorbed to a platinum surface via an olefinic group. They furthermore hinted at the possibility of modulating the coordinative properties of the interface through the control of the electrode potential. Cheek and Nelson reported on the determination of Ag (I) from the solution using modified carbon paste electrodes. They reported a truly remarkable detection limit. M. Oyama and Anson reported on the use of polymer modified electrodes capable of incorporating metal complexes either by coordination to pyridine groups in the polymer or electrostatic binding to polycationic or polyanionic polymer films. They reported that they could incorporate ions from solutions as dilute as 5 x 10^-8 M. These studies point to the feasibility of using not only metal/ligand interaction but electrostatic effects for performing electroanalysis.

Cox and Majda incorporated Fe(II) onto a platinum electrode modified with absorbed adenosine 5-monophosphate and subsequently determined the amount of incorporated ions via cyclic voltammetry. Price and Baldwin reported on the use of ferrocene carboxaldehyde for the determination of aromatic amines absorbed on the surface of a platinum electrode. They reported the detection limits that are equal to 10^-7 M. These authors also point out the different aspects (such as saturation) that must be kept in mind when attempting to use these modified interfaces for analytical purposes.

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