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Graduation date: 1999

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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

The application of flow injection analysis into the simultaneous determination of two or more components has been challenging for many years. Various detectors such as ultraviolet/visible absorption, fluorescence, and electrochemical detectors, have been used individually or in combination with each other. Combining two optical detectors such as fluorescence and ultraviolet/visible absorbance, however, has always been challenging due to their incompatibilities. However, the recent developments in fibre optics, solid-state light sources and miniaturised charged coupled devices (CCD), allow novel designs and most of the incompatibilities be circumvented. A flow injection manifold can now be adapted so that only one flow cell is used along with a diode array CCD detector that can detect both fluorescence and absorbance simultaneously. The initial development and testing of such dual detection system is described in this thesis.

Thesis (doctoral)--Lund University, 1994.

Thesis (doctoral)--Lund University, 1994.

The applicability of the technique of inductively coupled plasma mass spectrometry to the analysis of geological samples was investigated using a variety of sample introduction techniques including: solution nebulisation; slurry nebulisation; flow injection; electrothermal vaporisation; and laser ablation, Solution sample introduction is limited by the amount of time required to prepare the sample, and the relative intolerance of the technique to high concentrations of sample matrix. The maximum level of dissolved solids for a refractory matrix such as a digested igneous rock was found to be 0.2% w/v. Good accuracy and precision are achievable. Acceptable results can be obtained using slurry nebulisation. However, standardisation is a problem due to the difference in response for aqueous and slurried analytes. Calibration against aqueous standards and the use of an internal standard is therefore precluded. In addition, the preparation of stable slurries is a highly skilled and time consuming task. Flow injection analysis offers the most benefit to the geochemical analyst. Flow injection was found to increase sample throughput and, more important, to improve matrix tolerance by a factor of l0x, thus allowing the direct determination of the platinum group elements and gold in geological samples without pretreatment. Small samples, such as fluid inclusion leachates can also be analysed without dilution and the matrix effects experienced when analysing samples containing high salt concentrations can be reduced by careful control of dispersion. The potential for increased detection limits by electrothermal vaporisation was not proved for geological materials due to the same matrix tolerance problems which limit detection limits in solution work. Laser ablation sampling allows direct analysis of the solid but quantitation requires matrix matched standards or independent variable internal standardisation, limiting the applicability of the technique for bulk screening. The use of laser ablation to analyse trace element concentrations in individual mineral grains has been investigated and partition coefficients for trace elements, including the rare earths in a large zoned pyroxene crystal, were determined.

As ~ 50% of global photosynthesis occurs in marine environments, the factors regulating this process e.g. trace metal availability, have an impact on the global carbon cycle. The key cyanobacteria genera Prochlorococcus and Synechococcus have an absolute requirement for Co. Dissolved cobalt (dCo) concentrations in the open ocean are extremely low (5–120 pM). A sensitive flow injection technique using chemiluminescence detection (FI-CL) was developed (detection limit 4.5 pM dCo, RSD ≤ 4%). Seawater samples must be UV-irradiated prior to analysis, in order to liberate organically-bound Co. A field study in the Sargasso Sea, demonstrated that aerosol Co was significantly more soluble than aerosol Fe over a range of aerosol dust deposition fluxes (1–1040 μg Fe m-2 d-1) (8-100% for Co versus 0.44-45% for Fe). The dry deposition flux of aerosol Co was of the same order of magnitude as the advective upwelling flux (47-1540 pmol m-2 d-1 and 1.7-1430 pmol m-2 d-1 respectively). Wet deposition, dominated the total aerosol flux (~ 85%). The vertical distribution of dCo influenced Prochlorococcus abundance. A regional study in the eastern North Atlantic gyre demonstrated that the highest rates of N2 fixation occurred with the highest dFe concentrations (9.8 nM N L-1 h-1, 0.6 nM respectively). No increase in primary production following additions of trace metals (Co, Cu, Fe, Zn) was observed. The addition of N resulted in an increase in primary production. However, there was no synergistic effect of trace metal plus N addition, suggesting that alleviation of N-limitation shifted the system to P-limitation. On a meridional transect from ~ 50°N–50°S in the Atlantic Ocean, the highest concentrations of dCo (> 80 pM) coincided with low-O2 (< 150 μM) upwelled water. The lowest dCo (< 20 pM) was observed in the eastern North Atlantic gyre. Lateral advection of continental Co and upwelling were identified as important sources of Co. The highly efficient recycling of Co in the euphotic zone is an important additional source.

Hydrothermal fluids near and above the critical point of water have unique and potentially very useful thermophysical properties. At present, the lack of knowledge of supercritical water chemistry hinders implementation of innovative hydrothermal technologies. The development of new experimental methods and application of molecular modeling tools is clearly warranted to provide a better understanding of the complex properties of aqueous systems at elevated temperatures and pressures. The thermodynamic, dielectric and transport properties of hydrothermal fluids are investigated using Molecular Dynamics (MD) simulation and flow injection techniques. The spatial hydration structures and self-diffusion coefficients of phenol, aniline and naphthalene in aqueous infinitely dilute solution are examined from ambient to supercritical conditions by means of MD simulations. It is shown that the solvation shell around aromatic molecules undergoes significant changes along the liquid-vapour coexistence curve and, essentially, disappears at supercritical conditions. The changes in hydration structures are reflected in the values of the self-diffusion coefficients which dramatically increase near the critical point of water. The thermodynamic and dielectric properties of the Simple Point Charge Extended (SPC/E) water model are examined over a broad range of sub- and supercritical states. Accurate thermodynamic and dielectric equations of state (EOS) for the SPC/E water model are presented. The parameterizations provide the most accurate, up-to-date description of the properties of high-temperature SPC/E water, thus enabling for the direct comparison of molecular simulation results with experimental data via the corresponding states principle. The experimental methodology for the study of aqueous fluids at extreme conditions by using the ex situ flow injection technique is presented. The methodology significantly simplifies the technical aspects of flow injection analysis in hydrothermal fluids as sample injection and detection are performed at ambient temperature, thus allowing the use of standard on-line detection methods. The proposed ex situ experimental technique is applied to the examination of the hydrodynamic regime of a flow-through tubular reactor from ambient to supercritical water conditions. Application of the ex situ Taylor dispersion technique to measurements of the binary diffusion coefficients in hot compressed water is also presented. The ex situ flow injection methodology provides a basis for further development of flow injection analysis techniques at supercritical water conditions. / Thesis (Ph.D, Chemistry) -- Queen's University, 2009-03-05 17:39:30.197