Electrochemical generation-collection devices have potential for application in a wide range of analytical devices, both as free standing sensor systems and as components in analytical systems such as high performance liquid chromatography (HPLC) or flow injection analysis (FIA). The underlying principle is that an electrochemical reaction on one element is used to generate some chemical species which is then transported by diffusion or diffusion and convection to a second electrode where the electrochemical reaction is reversed. The fraction collected is a function of device geometry, operating conditions, any reaction of the generated species in bulk solution and mass transport.
This thesis describes the construction of generation-collection sensors comprising coplanar inlaid microelectrodes of different size and shape: ring-disc and disc-disc in sizes ranging from 10 m to 100 m. Fabrication techniques including sputter-coating and embedding of wires were developed and are described.
The sensors were characterised using scanning electron microscopy and their electrochemical characterisation was achieved using reversible outer sphere redox couples including ferrocene derivatives, ruthenium hexaammine (III/II) and ferro/ferricyanide. Experimental data are given for the effects of geometry, size and generator current density, particularly where this would affect the uniformity of the flux. Tests were also undertaken in specially built flow cells to assess their viability for application in FIA and LC detection. Where possible, performance in both the steady state and transient mode were compared with numerical and analytical models.
Three specific bioanalytical applications were investigated and are described: (i) detection of peptides and amino acids using electrochemically generated bromine/ hypobromite (ii) electrochemical biuret detection and (iii) determination of titratable acidity and alkalinity (buffer capacity). Results for (i) showed more complex behaviour with the Pt-Pt dual microelectrode than that has been reported for macroelectrodes under similar system. Voltammetric results are reported. Electrochemical biuret systems showed less improvement in sensitivity with the generation-collection mode to
small peptide molecules. For the buffer capacity sensor, both disc-disc and ring-disc geometries were investigated in a range of sizes 25 to 75 m for the disc and approximately 1 m for the ring. A pH sensitive surface was prepared by the deposition of hydrated iridium oxide on gold. Local pH changes were effect by electrolysis of the buffer solution. Experimental works emphasised the importance of controlling the current density to ensure that buffer capacity was not exceeded. An analytical model was of great use in optimising the device. Results are reported for various buffer systems comparing experiments with steady-state theory.