The development of a simple, semi-reversible, colorimetric oxygen sensor based on the redox chemistry of 2,6-dichloroindophenol in the presence of fructose and tetrabutylammonium hydroxide is described. The sensor is colourless in the absence of oxygen, but gives a strong blue coloration in oxygen at >30 Torr and quantitative analyses are possible between 0 and 50 Torr. The second type of sensor examined is based on the oxygen quenching of luminescence emitted from polymer encapsulated: platinum octaethylporphyrin, palladium octaethylporphyrin or tris(4,7-diphenyl-1,10-phenanthroline) ruthenium (II). Several means of collecting data from such sensors are evaluated. Gated fluorimeters can give erroneous data unless the natural and quenched lifetimes of the lumophores lie in the range 200 μs - 4ms. Several factors affect the oxygen sensitivity of these films including humidity, which depresses the sensitivity by 42% when using ethyl cellulose as the encapsulating matrix and by 14% when using cellulose acetate butyrate. No significant humidity effect is observed when using silicones, polyvinylchloride or polystyrene. The non-linear relationship between quenching efficiency (I<SUB>0</SUB>/I or τ<SUB>0</SUB>/τ) and partial pressure of oxygen observed in these films was examined and a simple Freuchlich power law shown to fit response data from six sensors which show a 600 fold variation in oxygen sensitivity. The non-linearity is a result of a site distribution in the sensor film and this has been further investigated using initial rate studies and distribution modelling. Such studies indicate that simulated data from a simple uniform distribution in the quenching rate constant (and/or oxygen solubility) gives good fits to experimental decay curves from the six different sensing systems examined. The required model parameters are easily accessible from experimental data and consistent with those calculated for diffusion controlled quenching by oxygen.

An instrument has been developed to determine the viscosity of liquid samples. It is in effect a modified Ostwald viscometer. A sample aliquot is injected into a carrier stream of similar viscosity to the sample, flowing along a tube of 0.086cm i.d. The passage of the sample is detected at a suitable point down stream and the viscosity of the sample may be determined from the sample velocity or alternatively under "Taylorian" conditions of slow flow rates, a relationship between peak height and (t/+i)9s has been found to exist. Chemical interaction between the sample and carrier, most probably in the form of hydrogen bonding has been found to cause deviations from linearity whereas in systems where no interaction can occur linear relationships have been found to exist for both relationships. The use of calibration curves based on standards of similar composition to the unknown sample should take into account any anomolies occuring in the system, thus enabling the viscosity of the sample to be determined. The instrument is microcomputer controlled, this includes the sample injection, maintenance of a constant temperature throughout the whole flow system via a thermostated water bath and water jacket housing thermistors which relay the temperature to the microcomputer, data collection from the detectors, processing and displaying results to the user, and balancing detector circuits. Two microcomputers have been used, MOUSE developed at AERE, Harwell, and a Commodore 32K PET. The MOUSE collects all the data prior to transmitting it to the PET for the data processing. This distributed computing approach has ensured rapid data collection and ability to perform complicated data processing routines on the data. Precisions of 0.2 to 0.3% have been obtained for selected systems, when the sample volume is 3071 and the time of determination 10-20 sec. In addition the thesis is concerned with automating FIA by microcomputer; several measurements of diffusion coefficents have been made by this method.

The analysis of photographic developing solutions presents an interesting and challenging problem for the analytical chemist. The developing agents themselves contain a wide range of components of various different chemistries, both inorganic and organic components are present at a wide range of concentrations. The developing agents as well has having a complex chemistry of their own, on use, are further complicated by the formation of products which can further affect the developing solutions performance. This work uses a variety of chromatographic and mass spectrometric techniques to examine a range of compounds present in the black and white Kodak developer RA2000. Emphasis is given to the application of these techniques to solving the analytical problem. The first chapter gives a theoretical introduction to mass spectrometry and liquid chromatography, with a discussion on the general principles in interfacing the two techniques. Chapter two gives a theoretical introduction to photography as well as an in depth discussion of developing solutions, specifically the RA2000 black and white developing solution. Analysis of RA2000 by liquid chromatography and capillary electrophoresis is also described. Chapter three provides an in depth discussion of solid phase extraction techniques as an alternative sample preparation method to liquid / liquid solvent extraction. Analysis of RA2000 by solid phase extraction and liquid chromatography was carried out in an attempt to concentrate the components formed after use, as well as to try and separate out the heavily concentrated compounds. Chapter four describes the analysis of RA2000 by liquid chromatography-thermospray-mass spectrometry and liquid chromatography-particle beam-mass spectrometry. An in depth discussion of both techniques is given. A column switching arrangement was used to allow analysis of the lower concentration components.

No description available.

The adaptation of two clinical instruments for the <i>in vivo</i> measurement of hepatic levels of copper and iron using neutron activation is described. The neutron activation instrument is based on a 4 GBq <SUP>252</SUP>Cf neutron source which can deliver different intensities and dose-rates, while the whole body counting facility, located in the adjacent laboratory, comprises of four NaI(Tl) crystals heavily shielded by lead. Due to the close proximity of the two instruments, during a neutron irradiation procedure, the background counts in the detectors in the next room are raised primarily because of iodine activation. Trials of various neutron shielding material have shown that one of the most effective and easily incorporated shields is cadmium placed all around the crystals. The feasibility of measuring the extent of liver copper burden has been established via two different thermal neutron capture reactions employing conventional and cyclic activation. The detection limits (2 standard deviations of the net peak counts) obtained for hepatic copper are 160mg and 200mg for an incident dose equivalent of 30mSv and 39mSv, for the conventional and cyclic methods respectively. Repeated irradiations of liver phantoms containing iron solution have shown that using the delayed, fast neutron reaction, iron can be measured with a reproducibility of 7.3% for a radiation dose equivalent of 36mSv. This relates to a detection limit of 1.2g iron for the liver. The two instruments have been calibrated for the <i>in vivo</i> measurement of copper and iron, and the potential for measurements of chlorine, manganese and magnesium highlighted.

No description available.

No description available.

No description available.

The main objective of this thesis was to contribute to the optimisation of the biosensing of two species that play an important role in living organisms, i.e., protons (H+) and nitric oxide (NO). The intracellular imaging and quantification of these species was achieved using fluorescence based nanoparticles and fluorescent molecular probes in combination with confocallaser scanning microscopy (CLSM). A novel photoinduced electron transfer (PET) based pH nanosensor was reported to improve the signalling of acidic organelles in cells. A PET-based pH ligand incorporating a thiolated moiety was synthesised and used to stabilise gold nanoparticles. The free ligand and the PET-nanosensor were unambiguously characterised and their fluorescence emissions were recorded in acidic and basic media. The fluorescence emission of the free ligand was quenched in alkaline conditions and enhanced in an acidic environment. The PET- nanosensor afforded a similar ON-OFF switching process in acid and basic environments. The PET-nanosensor was used for intracellular imaging of acidic environments in Chinese hamster ovary (CHO) cells by CLSM. The internalisation of the nanoparticles by the cells was confirmed recording images and fluorescence emission spectra of the PET-nanosensor from within the cells using CLSM. To determine the pH of individual regions within the intracellular environment, a ratiometric PET-based nanosensor (ratiometric pH nanosensor) was synthesised. The PET based pH- sensitive ligand and a synthetic rhodamine derivative ligand were used to stabilise gold nanoparticles yielding the ratiometric pH nanosensor. The fluorescence emission of the ratiometric pH nanosensor was recorded in acidic and basic media using a single excitation wavelength. The variation of the fluorescence signals of the ratiometric pH nanosensor enabled ratiometric fluorescence measurements of pH between 3.5 and 6.5. The ratiometric pH nanosensor was used for intracellular imaging of living CHO cells using CLSM. The fluorescence emission spectrum within CHO cells confirmed the internalisation of the ratiometric pH nanosensor since the spectrum was composed of the characteristic bands of both ligands. Cc-localisation experiments using a known marker of acidic organelles strongly suggested that the ratiometric pH nanosensor accumulated in the acidic organelles within the CHO cells. The ratiometric pH nanosensor was utilised to determine the pH of different regions in live cells. The fluorescence emission spectra of the regions where the pH nanosensor was accumulated within the cell were acquired and the pH of those different regions within the CHO cells was calculated. The estimated values of pH were in agreement with the values of pH reported in the literature for acidic organelles. The chemical reactivity of l,2-diaminoanthraquinone (DAA), a fluorescent probe for NO, when used for intracellular measurements was studied. DAA is an ortho-diamino compound and is postulated to react with NO in an oxygenated medium leading to the formation of a l,2,3-benzotriazole derivative (DAA-TZ). The formation of DAA-TZ when DAA reacts with NOj02 within cells has not been demonstrated previously. The objective of this part of the thesis was to confirm that DAA-TZ is the species formed intracellularly when OM reacts with NO/02. Independent intracellular evaluations of DAA and DAA-TZ were performed. RAW 264.7 macrophage cells were loaded with DAA-TZ and DAA under conditions of unstimulation and stimulation with interferon-y and lipopolysaccharide to induce the production of NO. CLSM was used for the intracellular studies providing images and fluorescence emission spectra of the cells. The results presented confirmed the intracellular production of DAA-TZ when DAA reacts with NO in the biological environment.

No description available.