Year

1990

Degree Name

Doctor of Philosophy

Department

Department of Chemistry

Abstract

Derivatisation methods for improved electrochemical detection in flowing solutions have been developed and applied to the determination of various compounds. The schemes described are based on chemical or photochemical reactions and are applicable to flow injection analysis and to high performance liquid chromatography.

Photochemical derivatisation and subsequent electrochemical detection have been carried out using the photoelectrochemical (PEC) approach in which photolysis of the analyte and detection of the photoproduct take place within the detector cell. Three modes of irradiation that differ in the position of the irradiation point with respect to the position of the working electrode are described.

Implementation of these irradiation modes has been achieved by designing PEC flow cells employing either the thin-layer or the wall-jet geometry. Electrochemical and PEC parameters describing the analytical performance and efficiency of the PEC cells have been evaluated. A method for determining the amount of light absorbed inside PEC cells has been developed.

In one irradiation mode the light is introduced into the cell through an optically transparent working electrode, a number of which have been characterised. Irradiation of the electrode surface has been shown to produce background photocurrents resulting from surface photoeffects. To minimise these effects, a detection technique utilising pulsed irradiation and current sampling techniques has been investigated.

Enhancement of detection of some analytes has been achieved by use of chemically modified electrodes with electrocatalytic properties. Electropolymerised films containing ruthenium centres have been found to produce the best results.

The practical application of PEC detection has been demonstrated with the determination of nitrosamines, explosives, alcohols, sugars as well as the speciation of thallium ions and online removal of dissolved oxygen for anodic stripping voltammetric analysis.

Conventional chemical derivatisation has been employed to detect metals by an indirect amperometric method. The method is based on the postcolumn reaction of a dithiocarbamate ligand with the metal ions.

The addition of derivatising solutions through a porous membrane located in the vicinity of the working electrode has been investigated. Electrochemical control of the porosity of conducting membranes has been utilised to control the transport of various reagents.

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