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Reference: Moorcroft, Matthew James., (2002). Electroanalysis at activated electrodes. DPhil. University of Oxford.Citable link to this page:

 

Electroanalysis at activated electrodes

Abstract: This thesis details advances made within the field of electroanalytical chemistry throughthe use of working electrodes that have been activated through application of ultrasound,heat, geometry, chemical modification or composition.Initially the thesis reports the enhanced analytical utility of chemically andcompositionally modified working electrodes when directed towards the detection anddetermination of NO3¯ and NO2¯ anions in environmental samples. This has beenachieved through the use of electrodes that have been a) modified with a Cu deposit andb) fashioned from a Cu-Ni alloy. Nitrate and nitrite anions have been successfullydetermined in a variety of passivating matrices, at analytically relevant detection limits ofthe order of 10-6 M with a dynamic linear range extending from 10 to 200 μM. Themethods presented have been shown to surpass existing electrochemical techniques interms of nitrate/nitrite speciation through separation of the voltammetric signals, whereexisting analyses have reported the intereference of both species when present in thesame solution. The use of ultrasound as a further enhancement to the sensitivity andversatility of the electrochemical detection of nitrate at a chemically modified electrodeis then presented. The influence of ultrasound is shown to remove a portion of thedeposited copper, but a significant catalytic layer remains, resulting in greater sensitivityduring insonation.The effect of temperature on electrochemical systems involving one- and two-electronredox reactions of K4Fe(CN)6, Ru(NH3)6Cl3, Fe(C5H5)2,N,N,N',N'tetramethylphenylenediamine, N,N'dimethylphenylenediamine and tris(4-bromophenyl)amine have been studied under hydrothermal conditions using a novelhydrodynamic method based on a conventional channel flow cell where the workingelectrode is heated by radio frequency radiation. The diffusion activation parametersobtained with the radio frequency channel cell and computer simulation were comparedwith independent data from microelectrode high temperature experiments. Theapplication of the heated flow cell as a tool for mechanistic studies is discussed with theinvestigation of the well characterised ECE reaction of m-iodo-nitrobenzene inacetonitrile, giving a value of 80 ± 5 kJ mol-1 for the activation energy of the rateconstant for the decomposition of the m-iodo-nitrobenzene radical anion. This representsthe first observation of an ECE or mechanistically complex reaction at a locally heatedelectrode.The work presented in the final two chapters of this thesis examines the enhancedactivation achieved from modification of the electrode geometry, and in particular theapplication of microelectrodes to the development of electroanalytical techniques. Theelectrochemical reduction of the inhalation anaesthetic agent enflurane (2-chloro-1,1,2-trifluoroethyl difluoromethyl ether) is reported at a variety of microelectrode substrates(Au, Ag, Cu, Pt and glassy carbon) with electrode dimensions varying from 5 to 60 μm.The solvents water, dimethylsulfoxide and acetonitrile were investigated along with thesupporting electrolytes potassium chloride, tetrabutylammonium hexafluorophosphateand various tetraalkylammonium perchlorates. The use of a gold microelectrode withdimethyl sulfoxide solvent and tetraethylammonium perchlorate as the supportingelectrolyte was found to give well-defined voltammetry. Linear calibration curves wereobtained between 0 and 2 % v/v (gaseous additions) or up to 135 mM (gravimetricadditions), offering scope for the development of a rapid, inexpensive electrochemicalgas sensor. The analytical utility of the system has been investigated in the presence ofoxygen and nitrous oxide in DMSO solvent. The superoxide anion radical, formed fromthe electro-reduction of dissolved oxygen, is shown to react with enflurane complicatingtheir simultaneous detection. The kinetics of the enflurane / superoxide reaction arefound to be first order with respect to both superoxide and enflurane with a rate constantof 0.25 M-1 s-1 determined by three independent methods: steady-state voltammetry,digital simulation of cyclic voltammetric data and UV/Vis spectroscopic analysis.

Type of Award:DPhil Level of Award:Doctoral Awarding Institution: University of Oxford Notes:This thesis was digitised thanks to the generosity of Dr Leonard Polonsky

Contributors

Compton, R. G.More by this contributor

RoleSupervisor

 

Richard ComptonMore by this contributor

RoleSupervisor

 Bibliographic Details

Issue Date: 2002Identifiers

Urn: uuid:6089e63c-3db2-4627-90e7-13763efcbd07

Source identifier: 603851699 Item Description

Type: Thesis;

Language: eng Subjects: Ultrasonics Nitrates Analysis Nitrites Tiny URL: td:603851699

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Author: Moorcroft, Matthew James. - institutionUniversity of Oxford facultyMathematical and Physical Sciences Division - - - - Contributo

Source: https://ora.ox.ac.uk/objects/uuid:6089e63c-3db2-4627-90e7-13763efcbd07



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