The work described in this thesis employs 'dual activation' methodologies and in particular sonovoltammetry to study a variety of electrochemical systems. First, the effect of 20 kHz power ultrasound on the electrochemistry of simple redox systems in both water and acetonitrile is explored and characterised for different cell geometries. A simple Nernst diffusion layer model is validated. Second, the use of insonation for efficient pre-concentration of target species in anodic stripping voltammetry (ASV) is reported. 'Sonotrodes', where the electrodes are incorporated into the ultrasonic horn tips are shown to offer particularly high rates of mass transport and additionally cause ablation of mercury from plated platinum electrodes. The key benefits of sonication are shown to be electrode depassivation and extraction plus rapidity and ease of determination, coupled with the lack of any sample pre-treatment for the detection of lead in both wine and petrol by ASV. Lead levels determined by this method and calibrated by use of standard microaddition are in excellent agreement with those obtained 'blind' by atomic absorption spectroscopy performed at independent laboratories. Third, the novel use of ultrasonically formed emulsions is examined for both analytical and synthetic purposes. The possibility of extracting species both out of an organic phase for analysis and into an organic phase for the synthesis of water-insoluble redox products is realised. Fourth, the sonovoltammetric determination of ascorbic acid in both aqueous solution and the fruit drink Ribena®, is compared with results obtained by laser activated electroanalysis, where low level laser illumination of an electrode is employed to maintain a fresh electrode surface. Small amounts of laser-induced thermal convection at the electrode result in steady-state voltammetry. The level of agreement is excellent between the two methods and also agrees very well with independent chemical analysis. Fifth, laser activated voltammetry (LAV) is further explored and a simple mass transport model verified. Damage caused by high power laser ablation is evidenced by atomic force microscopy (AFM). Applications of the technique for depassivation are illustrated by the reduction of toluidine blue dye and oxidation of ferrocyanide in the presence of blood proteins. The technique is further employed under channel flow conditions to elucidate an unambiguous mechanism for aqueous iodide oxidation at platinum electrodes in the absence of the usual build up of bulk iodine (as evidenced by AFM). Finally, the reduction of methylene green dye at platinum electrodes is used to compare and contrast sonovoltammetry and LAV with thermal and microwave dual activation techniques. The build-up of the passivating reduced form of the dye on the electrode surface, again seen by AFM, is removed by sono-emulsion and laser activation but not by microwave heating. However, greater conductivity is observed at higher temperatures and an electron-hopping mechanism is postulated.

The work contained in this thesis demonstrates that the introduction of power ultrasound into electrochemical systems can broaden the scope of techniques such as anodic stripping voltammetry. Analysis is facilitated by the well-documented phenomena associated with ultrasound, cavitation and acoustic streaming. Cavitation is caused by the collapse of voids created by ultrasonic compression and rarefaction of the solution and results in both localised high temperatures and pressures in the bulk solution and microjetting on the surface. Precise mechanistic details are still open to debate but there is evidence to suggest that shear forces at the interface when the electrode is flushed are responsible for removing organic material (particularly large species such as proteins) facilitating continuous cleaning and activation of the surface. Acoustic streaming has been shown to give diffusion layer thicknesses of the order of 1-10 μm depending on solvent and ultrasound power. The increased mass transport at such low diffusion layer thicknesses results in shorter preconcentration periods in electrochemical stripping voltammetry, greater sensitivity and a correspondingly lowered detection limit. Often ultrasound has been applied to highly passivating systems where conventional silent electroanalysis fails with the effect of transforming invisible or tiny voltammetric signals into large and quantitative responses suitable for sensitive and accurate analytical purposes. In Section IIthe relative contributions of acoustic streaming and cavitationally induced microjetting to the sonovoltammetric response is assessed. Chronoamperometry at insonated electrodes of both micro and macro dimensions, and differential pulse voltammetry (DPV) were used to explore the frequency and violence of cavitational events and the nature of the diffusion layer prevailing under steady-state electrolysis. The results lead to a physical model of an insonated electrode which may be described as a steady diffusion layer a few microns thick brought about by acoustic streaming which is occasionally and randomly punctuated by a cavitational event. The frequency and violence of the event is dependent on the solvent and ultrasound power, except at very short electrode-to-horn separation where the cavitational contribution becomes substantial. Section II concentrates on the implementation of the technique with applications to the detection of heavy metals in biofluids. In Chapter 4 sonoelectroanalysis is applied to the detection of copper bound within human blood protein and whole blood. It is shown that the enhancement of square wave anodic stripping peaks observed in ceruloplasmin and whole blood is not simply due to mass transport enhancement and cavitational cleaning effects alone but also the liberation of copper from the active sites in which it is bound prior to preconcentration. The results of a quantitative determination of total copper in two samples of whole blood were 1300 μg L^-1 and 620 μg L^-1, verified by independent blind analysis using atomic absorption spectroscopy (AAS). The need for rapid analysis of environmental samples can also be fulfilled using sonoelectroanalysis. In Chapter 5 fish gill mucus is used as a non-destructive biomarker for the detection of heavy metals by sono-square wave anodic stripping voltammetry (sono-SWASV). A quantitative assessment of copper content yielded values of 16 μgL^-1 and 21 μgL^-1 which compared favourably with independent blind analysis by AAS. The potential of the technique for detection of other heavy metals for example lead, was also demonstrated. Lead poisoning is recognized as a major environmental health risk and in Chapter 6 quantitative analysis of lead in artificial saliva from a realistic sputum volume, 220 μL, introduced to acetate buffer is investigated. An insonated preconcentration obviates the need for lengthy or degradative sample pretreatment by liberating the lead from the glycoproteins and other materials to which it binds in solution. Quantitative depassivation of the electrode surface by cavitational shearing maintained the analytical signal throughout the experiment where under silent conditions the signal diminished to zero with time. The detection limit in the analyte is 0.25 μg L^-1. Following this proof of concept, Chapter 7 goes on to apply the technique to the quantitative determination of lead and cadmium in real human saliva. Close agreement between lead concentration determined by sono-SWASV and independent and blind ICP-MS is reported for human saliva samples with detection limits of 0.5 μg L^-1 lead and 1 μg L^-1 cadmium in saliva. Section IV harnesses the benefits of acoustic emulsification. Power ultrasound is capable of forming droplets of micron dimensions with lower energy consumption than conventional emulsifiers. Chapter 8 acoustic emulsification is employed in the detection of vanillin (4-hydroxy-3-methoxybenzaldehyde) in vanilla essence using ethyl acetoacetate as a novel electrochemical and sonoelectrochemical solvent. Contrasting with silent voltammetry, ultrasound facilitates emulsification and extraction of vanillin in the extract permitting an analytical square wave voltammetric signal to be obtained. Close agreement with a blind analysis of the samples using HPLC-UV is observed with a limit of detection in the biphasic medium of 0.020 mM. In Chapter 9 acoustic emulsification is utilized in the solvent extraction of copper. Ultrasonic emulsification of an aqueous phase containing copper ions with the N-benzoyl-N-phenyl-hydroxylamine ligand in an organic ethyl acetate phase was shown to facilitate the extraction of copper into the organic phase at 25°C. Subsequent emulsification with 1 M acid "back-extracts" or "re-strips" the copper into the aqueous phase prior to analysis via sono-SWASV. The technique necessarily removes contaminants present in the test solution since these will prefer to remain in the initial aqueous phase, or will transfer to the organic phase but are unlikely to be doubly transferred into the "clean" final aqueous phase. In Chapter 10 the technique is applied to the analysis of copper in the soft drink "Ribena® Light" with a detection limit of 2 μg L^-1 and copper in blood with a detection limit of 0.16 μg L^-1. In the latter case the analysis required a sample volume of 100 μL suggesting that a pinprick test may be feasible. Finally in Section V, the analysis of copper in the presence of surfactants is investigated. Surfactant adsorption has been shown to have a passivating effect on the electrode surface during anodic stripping voltammetric measurements. Effluent, both industrial and domestic, is commonly contaminated with surfactant and electroanalysis of heavy metals is frequently precluded. It is therefore desirable to formulate a new analytical strategy in waste water. This is facilitated by controlled experiments with known amounts of anionic, cationic or neutral surfactant which also provides an ideal model system for comparing the techniques introduced in earlier Chapters. "Direct" sonoelectroanalysis in the medium of interest is compared with biphasic sono-solvent double extraction and both are appraised in the light of novel sonotrode technology. This thesis concludes that sonoelectroanalysis is a powerful and versatile analytical tool that can be employed in an expanding range of applications. The examples given herein are pertinent to the major fields of medical diagnosis and the assessment of environmental pollution. They demonstrate that sonoelectroanalysis is a viable alternative to conventional analytical techniques which have the disadvantages of more lengthy sample pretreatment and cost.

This thesis reports voltammetric and quartz crystal microgravimetric studies of the binding of metal complexes to nucleic acids in solution and immobilised on metal surfaces. Cyclic voltam iet y and steady-state microelectrode voltammetsy were applied to the solution phase interactions between metal complexes and nucleic acids. The binding constants were obtained by the analysis of bound and free metal complex concentrations. The binding of N, N, N-1-propylthyminedimethylaminomethylferrocene (Fc-Th), N, N, Ntrimethylaminomethylferrocene (Fc-NMe3), bis(hexamethybenzene)iron(II), hexamuiiineruthenium( III), tris(1,10-phenantlu-oline)iron(II) and tris-(bipyridyl)iron(II) to DNA and RNA was observed. The application of microelectrode voltammetry for metal complexnucleic acid binding studies has not been reported before and this thesis demonstrates the advantages of the method due to increased signal-to noise ratio and better discrimination between free and nucleic acid-bound metal complex. These voltammetric results showed the binding of Fc-Th to DNA is stronger than the binding of Fc-NMe3 to DNA, indicating that even a single nucleobase can influence the binding. The binding of singly charged feirocenyl derivatives to DNA or RNA is mainly electrostatic plus some non-electrostatic contribution from interaction of the thymine with DNA. Fe(bz)22 binds to DNA electrostatically and the binding is senstive to ionic strength. Ru(NH3)63+ binds more strongly to DNA due to its higher charge. The binding of Fe(phen)32+, a known intercalator, is stronger than the binding of Fe(bipy)32+ to DNA and the measured binding constants were in agreement with previous reports, however more precise data could be obtained using the microelectrode technique devised in this thesis. This thesis also describes a novel modification of gold and platinum surfaces by the adsorption of 4-mercaptopyridine and subsequent methylation with methyliodide to produce a positively charged suface at which DNA adsorbs strongly. Cyclic voltammetry was applied to quantify the binding of Fc-Th, Fc-NMe3 , hexammineruthenium(II), and tris(1,10-phenanthroline) iron(II) to DNA or RNA immobilised on a gold electrode. A detectable binding of Fc-Th, Ru(NH3)63+ to DNA was observed, while no bound. FcNMe3 and Fe(phen)32 were detected using cyclic voltammetry. The difference in binding to immobilised DNA compared to dissolved DNA could be rationalised by the effect of the electrostatic interactions of the metal complexes with the charged pyridinium monolayer. Quartz crystal microfravimetry was used to estimate the surface coverage of DNA, Fc-Th, Ru(NH3)63+ and Fe(phen); '+on gold and platinum crystals modified as above. Crystal admittance measurements showed no significant change on DNA adsorption indicating approximate rigid-layer behaviour. In agreement with the CV studies no binding of Fc- NMe3 was detected. Some binding of Fe(phen)32 was observed and the negative result of the CV experiment may be due to instability of the monolayer at the high potentials required to oxidise Fe(phen)32+. In general, the QCM results showed higher surface coverages than detected by CV. Two factors may be important, the absence of solution phase metal complex in the CV experiment leads to some desorption and the QCM measurements are complicated by the unknown extent of solvation of the metal complexes.

Thesis (M.S.)--West Virginia University, 2004. / Title from document title page. Document formatted into pages; contains xii, 93 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 88-93).

Thesis (Ph. D.)--University of Hong Kong, 1996. / Includes bibliographical references (leaf 487-524).

Thesis--University of Wisconsin--Madison. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 223-228).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1985. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 292-307).

Philosophiae Doctor - PhD / Organic noncyclic compounds were used in the development of immunosensor for rapid fish species detection. Flourene derivatives show unique chemical and physical properties because they contain a rigid planar biphenyl unit, and the facile substitution at C9 position of the flourene can improve the solubility and processability of materials containing flourene without significantly increasing of steric interactions in the compounds backbone. 9-(4- methoxyphenyl)-9H-xanthen-9-ol is bulky, rigid and has an hydroxyl moiety that may act as a hydrogen – bond donor, as well as a pyranyl oxygen which is a potential hydrogen –bond acceptor. We have successfully synthesised 9,9’-(ethyne1,2-diyl)bis(flouren-9-ol) by reflux method and 9-(4-methoxyphenyl)-9H-xanthen-9-ol through stirring at room temperature. The products were characterised using spectroscopic methods and were found to be both UV/Vis active (λmax = 400 nm flourene derivative and λmax = 337 nm xanthene derivative ) and fluorescent (440nm and 467nm flourene derivative and 344 and 380 xanthene derivative). These compounds were drop coated onto commercial glassy carbon electrode (GCE) to produce thin films. Scan rate dependent cyclic voltammetry (CV) confirmed the electrodynamics of the thin films to be consistent with monolayer diffusion (De = 1.37x10-21 cm2/s flourene derivative and De = 9.79x10-21 cm2/s xanthene derivative). Surface concentration was estimated to be 1.55x10-13 mol cm-2 flourene derivative and 2.00x10-13 mol cm-2. These compounds were used for the inclusion of parvalbumin antibodies immobilised onto clathrate platform by incubation and were evaluated as immunosensors for fish species identification. The antibody/antigen binding event was evaluated using UV/Vis spectroscopy, electrochemical impedance spectroscopy (EIS) and atomic force microscopy (AFM). The immunosensor response to parvalbumin in real samples of snoek (an indigenous fish species), tuna, fish paste, eyeshadow, lipstick, omega 3&6 and Scott's emulsion was evaluated. The sensitivity as calculated from EIS for each immunosensor was found to be 5.36x104 flourene derivative immunosensor and 4,11x104 xanthene derivative immunosensor and the detection limit of 1.50 pg/ml flourene derivative immunosensor and 2.42 pg/ml xanthene derivative immunosensor. The antibody/antigen binding was monitored as decrease in charge transfer resistance and increase in capacitance by EIS. The interfacial kinetics of the immunosensors were modelled as equivalent electrical circuit based on EIS data. The UV/Vis spectroscopy was used to confirm the binding of the antibody/antigen in solution by monitoring the intensity of the absorption peak.

When metal pollutants exist in natural water, their toxicity is dramatically dependent on the chemical species. Numerous sophisticated techniques and instruments have been developed to detect metal pollutants at very low concentration levels. However, one important factor is often ignored, i.e., rarely is species determination required. Electrochemical (EC) methods have the particular advantage of being, in principle, a species-sensitive method rather than an element-sensitive method for the study of metal speciation in natural waters. The goal of this research was to develop an instrument using the EC technique for speciation and general voltammetric studies. It was accomplished by designing a flow-through EC cell containing multi-electrodes to which various fixed potentials over a selected range were applied. A special potentiostat was designed to supply a selected potential to each electrode in the cell. Potential control was provided by placing a combined counter-reference electrode at circuit ground and connecting each working electrode to the inverting input of a current follower which had a potential applied to its non-inverting input from two digital-to-analog converters and a resistor network. Integrating current followers were used for measuring signal currents generated by the electrolytes samples on each electrode. A multiplexing circuit, including an analog-to-digital converter, was used to fulfill data acquisition. These circuits were interfaced to a computer and the readout was a pseudo-voltammogram which is a plot of amperometric currents versus various applied fixed potentials on each electrode. Details of the instrumentation, software, and some initial results are described.

No description available.