Year

1993

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

The continued advancement of electrochemical sensing is inextricably linked with the development of modified electrodes. New preconcentration schemes, utilising analyteelectrode interactions not normally employed in conventional sensors, open up a number of potential applications for these electrodes. One flexible route to the generation of electrode modifiers is through the use of electrochemically generated polymers to functionalise the electrode surface.

This work has investigated the use of a number of monomers for electrode modification. Monomers studied include pyrrole, thiophene, 3-methylthiophene, 2,2'-bithiophene, Nethyltyramine and 4-vinylpyridine. The electrochemical generation of polymers from these monomers was studied and those found to deposit as reproducible coherent modifier layers were further investigated with a view to practical applications. Of the polymers studied polypyrrole was found to provide the greatest scope for use as an electrode modifier. This was due to the fact that, during the oxidation of the monomer to form the polymer, anions from the polymerisation solution are incorporated into the polymer matrix. As polypyrrole may be generated from either aqueous or acetonitrile solutions of the monomer and supporting electrolyte it is possible to incorporate a number of water soluble and water insoluble anions into the polymer matrix during electrosynthesis. None of the other monomers studied give this degree of flexibility in polymer growth.

The application of polypyrrole modified electrodes for sensing purposes and polypyrrole modified Reticulated Vitreous Carbon for sampling purposes has been the focus of this study. The interaction of mercury(II) with a dithiocarbamate functionalised polypyrrole has formed the basis of a preconcentration device for this cation. Gold has also been preconcentrated onto polypyrrole coated RVC . The mode of interaction in this application appears to be a redox reaction between the polymer and the analyte.

Polypyrrole was found to be unsuitable for sensing applications that required modifiers with a low background signal. In this case polymers formed from either 4-(vinyl pyridine) [gold sensor] or N-Ethyltyramine [methylmercury sensor] were employed. The mode of electrode-analyte interaction with these electrodes was thought to be ionexchange and complexation respectively.

The effect of applied potential on the electrode-analyte interaction was studied and it was found that in some cases it could be used to enhance this interaction.

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