The ability to inexpensively and reliably detect organic compounds is important across a multitude of different areas of science. Benzene ring functional groups are found in a wide variety of biological molecules, (such as amino acids, DNA nucleotide bases and blood based components). The qualification and quantification of these compounds in a sample has been achieved by techniques such as high performance liquid chromatography (HPLC), gas chromatography (GC), mass spectrometry (MS) and nuclear magnetic resonance (NMR), amongst others. These techniques, however, often require cumbersome, expensive equipment along with exhaustive sample preparation techniques and are thus not necessarily suitable for portable in-situ analysis of these compounds. This thesis details the fabrication and characterisation of graphene modified electrodes that show an increased sensitivity towards biomolecular compounds such as dopamine, amino acids, and DNA. The graphene was synthesised using a novel semi-automated method which was performed using a bespoke apparatus designed to alleviate the labour involved in synthesising graphene by the sonochemical method. The method involved pumping an aqueous solution of the surfactant into a solution of graphite in water which was under constant sonication. When used in an electrochemical system employing cyclic voltammetry the graphene modified electrodes showed not only a lower limit of detection in all cases, but also a shift in peak position which allowed for simultaneous quantification of mixtures of compounds. This could not be achieved with screen printed carbon electrodes alone as different peaks often occur at similar potentials, making it difficult or impossible to quantify these compounds individually. Slower scan rates can often give rise to separate peaks, however this adds time to the experiment which is not necessary with graphene modification. The binding interactions of novel resorcinarene molecules were also predicted by molecular modelling techniques and then confirmed using NMR binding experiments. The resorcinarene was tested against a range of different analytes and showed a degree of specificity. The interaction between the two surfactant molecules and the graphene surface was also analysed to determine whether or not the resorcinarene molecules could be adsorbed onto graphene to produce a viable, molecularly specific electrode surface.

This thesis describes a study of angular effects in Auger electron emission from solid surfaces using a specially developed instrument, based on a static high resolution electron energy analyser, that allows Auger currents to be measured with almost any combination of incident beam angles and emission angles. The rate of Auger production as a function of depth was first of all examined by measuring the Auger emission angular distributions, from clean non-crystalline surfaces, using a wide variety of incident beam conditions. The rate of Auger production was found to be constant within the escape depth providing 2.5 ≤ E_p/E_c ≤ 24. Further experiments on various surfaces, with overlayers present, showed that the form of the Auger emission angular distributions could be used to determine whether or not the overlayer was uniform, and also to estimate its thickness. The angular variations of each part of the copper M_2,3VV doublet were measured for the first time from a single crystal copper surface. It was shown that the initial state of the Auger electron profoundly affects the emission angular distributions and this provided evidence that band structure effects could not be ignored when describing the initial state of the Auger electron. The lack of structure in the silicon L_2,3VV emission angular distributions was thought to be partly due to Auger electron originating in different types of surface site in the silicon surface. The angular distributions of the high energy Auger signals exhibited pronounced structure, independent of the initial state of the Auger electrons that could be correlated with the Kikuchi patterns end channeling patterns obtained at similar energies. Much of the structure in these signals could be qualitatively understood using the dynamical theory of electron diffraction. Finally these techniques were used to study the growth forms of various evaporated metal films.

A series of field and laboratory experiments were undertaken to examine the effects of incorporation of plant material on emissions of N<SUB>2</SUB>O from agricultural soils. The overall aim was to increase understanding of that part of the agricultural N cycle, associated with the release of N after incorporation of crop residues and green manures into soil, and subsequent N<SUB>2</SUB>O emissions to the atmosphere. N<SUB>2</SUB>O emissions from growing corps and following addition of various residues and green manures to soil were measured and compared. The effects of crop type, fertiliser application, cultivation techniques, soil type, and climatic conditions, and also of the addition of high C substrate in the form of paper waste, on these emissions were investigated. Emissions of N<SUB>2</SUB>O were increased after cultivation of soil, attributed to increased accessibility of organic matters to soil microbes, and improved gaseous diffusion. Emissions were higher following incorporation of plant material than emissions from bare soil. Generally, fluxes were increased within a few hours or days after cultivation and/or incorporation, but the effect was short-lived. Most of the N<SUB>2</SUB>O was emitted during the first 2 weeks. The magnitude and timing of N<SUB>2</SUB>O released within this period was highly dependent on temperature and rainfall following incorporation, and the cultivation technique employed. The C:N ratio of the incorporated plant material had a considerable effect on rates of decomposition, and on subsequent N<SUB>2</SUB>O production during nitrification and denitrification. Higher emissions were typically measured after incorporation of material with a low C:N ratio, such as legumes, than when material with higher ratios, such as cereal straw, was involved. When material with a high C:N ratio was added, N was immobilised. Nevertheless, the presence of high C:N paper waste increased N<SUB>2</SUB>O emissions from incorporated vegetable crop residues. This was attributed to the creation of more anaerobic sites in the soil. Emissions of N<SUB>2</SUB>O increased within a few days of applying mineral N fertiliser to spring-sown cereal crops. Again, these fluxes were short-lived. Use of <SUP>15</SUP>N-labelling in this experiment showed that approximately 50% of crop N at harvest was derived from applied fertiliser. In other experiments, the presence of a growing crop particularly a legume, increased emissions, compared with those measured from bare soil. The measurements of soil mineral N (the substrate for N<SUB>2</SUB>O) were compared with the amounts predicted by various N models. Practical suggestions were made for ways to lower N<SUB>2</SUB>O emissions from agricultural systems, thereby reducing detrimental effects on the ozone layer and global warming.

PDMPO (2-(4-pyridyl)-5-((4-(2dimethylaminoethylaminocarbamoyl)methoxy)phenyl) oxazole), has unique silica specific fluorescence and is used in biology to understand biosilicification. This ‘silicaphilic’ fluorescence is not well understood nor is the response to local environmental variables like solvent and pH. We investigated PDMPO in a range of environments: using UV-visible and fluorescence spectroscopy supported by computational data, dynamic light scattering and zeta potential measurements to understand the PDMPO-silica interaction. From absorption data, PDMPO exhibited a pKa of 4.20 for (PDMPOH22+ to PDMPOH+). Fluorescence emission measurements revealed large shifts in excited state pKa* values with different behaviour when bound to silica ( pKa* of 10.4). There is size dependent shift in pKa*. pKa* value of 9.60, 10.20, 10.50, 11.40, 11.44 was retrieved for 22 nm, 30 nm,50 nm, 77 nm and 133 nm particles respectively. PDMPO bound to silica particles is located in the Stern layer with the dye exhibiting pH dependent depolarising motion. In aqueous solution, PDMPO showed strong chromaticity with correlation between the maximum emission wavelength for PDMPOH+* and dielectric constant (4.8-80). Chromatic effects were also observed for silica bound dye which allow its use as a direct probe of bulk pH over a range far in excess of what is possible for the dye alone (3-5.2). The unique combination of chromaticity and excited state dynamics allows PDMPO to monitor pH from 3 to 13 while also reporting on surface environment opening a new frontier in the quantitative understanding of (bio)silicification. A linear relationship was observed between PDMPO emission ratio and zeta potential measurements were used to determine charge on the silica nanostructures exhibited by Equisetum arvense and Nitzschia stellate. This thesis also report an optical sectioned planar format assay (OSPFA) using confocal microscopy to study silica biomolecule interaction (amino acids and silica binding peptides ( pep 1) ) using a PDMPO displacement assay.

This work describes the use of laser spectroscopy and ab initio calculations in the investigation of several new electronic transitions in metal-containing free radicals. These free radicals were prepared in a supersonic jet by laser ablation of solid metal samples in the presence of appropriate precursor molecules. The first spectroscopic observation of the Ga-N2 van der Waals cluster is reported. Laser-induced fluorescence (LIF) spectra have revealed two strong band systems in the near ultraviolet correlating with transitions of atomic gallium. Long vibrational progressions due to activity in the van der Waals stretching mode were observed in both systems. Supporting ab initio calculations on the group 13 atom-nitrogen molecule clusters confirm that these clusters are linear in their ground electronic states. New electronic transitions of the CaNC and SrNC free radicals have been identified in the near ultraviolet. These include the D˜ -- X˜ transition of CaNC and the D˜ -- X˜ and E˜ -- X˜ transitions of SrNC. The first jet-cooled investigation of the SrNC C˜ -- X˜ transition was also performed. All the spectra showed complex vibrational structure which has been attributed to activity in the bending mode. This has been used to infer that a non-linear equilibrium geometry is adopted in the upper electronic states, in contrast to the linear ground electronic states. The first observation of the lowest 2Delta state of a strontium-containing free radical is reported, that of SrCCH. This new excited electronic state is accessed by the orbitally-forbidden B˜' 2Delta-X˜ 2Sigma + transition. Spin-orbit and vibrational structure have been seen in spectra of SrCCH and SrCCD and confirmed the assignment. Finally, observation of a new transition in an unidentified gallium-containing molecule is reported. Two progressions corresponding to two different vibrational modes of the molecule are seen in the spectrum. Potential spectral carriers, including Gax clusters and other gallium-containing molecules formed by reaction with impurities, are discussed in an attempt to explain the observed spectrum.

No description available.

No description available.

Non-methane hydrocarbons (NMHCs) have been measured in the boundary layer and free troposphere to investigate their behaviour under different atmospheric chemical regimes. Ambient air samples were collected using the Whole Air Sampling (WAS) system aboard the UK atmospheric research aircraft - FAAM BAe 146 - and analysed using a dual-channel gas chromatograph coupled with the flame ionization detectors (FID). Hydrocarbon ratios were used to determine the presence of nitrate radicals in the atmosphere during summer, winter and autumn phases of the ROle of Nightime chemistry in controlling the Oxidizing Capacity of the AtmOsphere (RONOCO) campaign. The extensive data set showed that the pentane n – iso isomer pair were particularly useful when diagnosing the presence of different oxidants during day, night, dusk and dawn. A hydrocarbon variability versus lifetime approach applied to the entire winter and summer datasets proved useful in determining the presence or absence of the nitrate radical. Free tropospheric NMHC measurements were made over the period January 2009 - January 2011 above the UK. These data provided a rare description of the seasonal variations in this region of the atmosphere. A comparison of this work with earlier UK free troposphere studies made twenty years ago, revealed a decline in the amplitude of the seasonal cycle by a factor of approximately two for acetylene, benzene and toluene. Airborne measurements of NMHCs have also been made in boreal forest fire plumes over Canada between 12th July 2010 and 2nd August 2010 as a part of the research project - Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS). The fire emission ratios for 29 different organic species relative to emission of CO have been derived. The comparison between observationally derived emission ratios and the GEOS-Chem Chemical Transport Model highlighted the influence of biomass burning as a large contributor to benzene, toluene, ethene and propene levels in many global locations.

This thesis presents the development of a portable lab-on-a-chip two dimensional gas chromatograph (GCxGC). A planar microfabricated system was designed and fitted within a modular built-for-purpose housing unit. The lab-on-a-chip device used acid etched borosilicate glass as the working substrate. The cost and ease of glass fabrication in this manner is attractive when compared to silicon, allowing for the formation of two capillary columns separated by channels designed to allow modulation of the eluent from the first (primary) column to the secondary. Not only were these channels circular in shape, but they also boasted similar dimensions to modern, commercially available fused silica GC columns. All working components needed to make field volatile organic compound (VOC) measurements, i.e. injector, columns, interfaces and detector, were, thus, encapsulated in a single ultra-portable microfabricated glass unit. The use of a miniaturised photoionization detector(PID) in conjunction with the glass chip is reported. The overall system had an attractive peak capacity and detection limit for VOCs, low power demand and an operating temperature range of 0 to 200 °C without cryogens. The miniaturised instrument, which offers a novel and alternative route to enabling microfabricated gas chromatography (GC) systems, is intended to be used in the first instance for atmospheric chemistry and air quality observations in relation to the work of the Atmospheric Chemistry research group at the University of York. It is envisaged that, if produced on a commercial scale, it could be used for a range of analyses where a field portable but highly sensitive and selective gas chromatograph capable of performing high-speed separations is required.

Whilst the capabilities of analytical techniques are ever-increasing, individual methods can provide only a limited quantity of information about the composition of a complex mixture. Interrogation of samples by multiple techniques may permit for complementary information to be acquired, and suitable data fusion strategies are required in order to optimally exploit such complementary information. A novel mid-level data fusion strategy has been implemented which uses two-stage genetic programming for feature selection and canonical correlation analysis such that highly discriminatory variables can be related together in a multivariate fashion. The approach offers an intuitive way to visualise variable interaction and their contributions to experimental trends.