Call number: LD2668 .T4 1956 H38 / Master of Science

Call number: LD2668 .T4 1953 C69 / Master of Science

The research described in this dissertation conclusively demonstrates the superior qualitative and quantitative performance of spectroscopic systems which employ a new class of optical detectors--charge transfer device (CTD) detectors. An overview of the operation and characteristics of these detectors, as well as theoretical models predicting their performance are presented. The evaluation of a unique prototype single element CID detector, a commercially available linear CCD detector, and a prototype two-dimensional CCD detector are described. Outstanding characteristics include the ability of the single element CID to quantitate photon fluxes ranging over eleven orders of magnitude, a quantum efficiency of the linear CCD in excess of 90%, and a read noise of the two-dimensional CCD of under 5 electrons. In addition, the use of the linear CCD for molecular fluorescence spectroscopy is demonstrated. A direct comparison of CCD and CID detection for atomic emission spectroscopy using a custom echelle system is described. The second part of these investigations focus on the design of spectrometers compatible with the format of these multichannel detectors. While a large number of spectrometer designs exist, the spectrometer and detector combination which produces the highest possible signal-to-noise ratio (SNR) spectra for a given experimental system is almost always desired. The investigations into optimum spectrometer design have led to the use of a unique spatial interferometer system. The performance of a common path interferometer using a linear charge-coupled device detectors is presented and compared to conventional dispersive systems. The throughput, resolution, and other practical factors are discussed. The common path system has a much larger light gathering ability compared to dispersive systems; however, spatial interferometry suffers from the multiplex disadvantages encountered with other forms of UV/Vis interferometry. A unique crossed interferometric dispersive arrangement allows the simultaneous acquisition of the spectral information while greatly reducing these multiplex disadvantages. Preliminary work on the crossed interferometric system is presented demonstrating significant reduction of these multiplex disadvantages.

Mass spectrometry is a widely used technique for the performance of elemental analysis: not only does it provides excellent limits of detection for a large number of elements, but it is also able to provide information about the isotopic distribution of the analyte. The radio-frequency quadrupole ion trap is a relatively new design of mass spectrometer, which offers the ability to confine charged particles for extended periods of time in a well defined volume by applying a radio-frequency oscillating voltage to an arrangement of three electrodes. A mass analysis of the trapped ions can be obtained by selectively extracting the ions from the cavity of the trap, where they can be detected by an electron multiplier. Despite its unique capabilities, to date the applications of the ion trap mass spectrometer have mostly been restricted to gas chromatography detection. Until recently, there have been very few attempts to use it for any other types of routine analysis. Our interest lies in the development of an instrument capable of performing a complete mass spectrometric elemental analysis of small volume liquid samples (a few (μL) at trace or ultra-trace concentration levels. The ability of the ion trap to accumulate ions in its cavity and to provide an entire mass spectrum of these ions in a single scan of the radio-frequency oscillating voltage applied between the electrodes, makes it a very interesting candidate for the ultra-trace analysis of small size samples. However, to perform an analysis on a sample with the ion trap the sample must first be vaporized; and if an elemental analysis is required, the sample will also have to be atomized. The graphite furnace atomizer used in atomic absorption spectroscopy offers a number of advantages which make it potentially useful for this purpose: it has a high transport efficiency of the analyte from liquid or solid state to the vapour phase, the ionization of the analyte in the furnace is very low (as required by the ion trap) and it handles small volume samples very well. A graphite furnace ion trap mass spectrometer was designed to fulfil the need of having instrumentation capable of multielemental mass spectrometric analysis of small volume samples containing traces of the analytes of interest. This document contains a description of the principles of operation of the ion trap as well as a detailed description of the instrument actually built. Data are presented in order to assess the capabilities of the instrument, as well as some of the problems encountered with it. The results obtained with the graphite furnace ion trap mass spectrometer allow us to conclude that the proposed design is not appropriate for the performance of elemental analysis, but is appropriate for mass spectrometric study of low boiling point compounds which can interfere with atomic absorption analysis: it is calculated that these compounds could be analysed at the ppm level. Promising results obtained with a set up in which the analyte is vaporized directly into the cavity of the ion trap through laser ablation are also presented. These limited results show the potential of this methodology for direct elemental analysis of solid samples. / Science, Faculty of / Chemistry, Department of / Graduate

Field and laboratory spectroscopy are sub-fields of remote sensing, where the radiometric data of materials are individually measured either where the materials occur in situ or in a controlled laboratory environment. Both applications require the use of a spectroradiometer to record this reflected electromagnetic radiation. The spectral properties of rocks from the Mambulu Complex in the Natal Belt have not been studied previously. Four dominant rock types, namely, massif-type anorthosite, leuco-gabbro, pyroxenite and magnetitite were sampled from the Mambulu Complex and their spectral reflectances measured. Absorption features were determined after continuum removal was applied to the spectra. Anorthosite showed absorption features at 480-490, 592, 603, 608, 627-726, 765, 1410, 1905-1955, 2200, 2250 and 2330nm. For leuco-gabbro absorption features were observed at 481, 950-1010, 1407, 1917, 2206, 2252, and 2300-2340nm. Magnetitite displayed absorption features at 414, 460-515, 620-715, 982, 1380-1480, 1800, 1905-1930 and 2145-2330nm. For medium-grained pyroxenite absorption features were present at 410-420, 483, 680, 977-993, 1410-1415, 1800, 1920, 2205, 2250, 2307, 2400 and 2430nm. Coarse-grained pyroxenite showed absorption features at 460-727, 979, 1000, 1401, 1422, 1800, 1913, 1930, 2203, 2258, 2321, 2388 and 2421nm. ANOVAs and Bonferroni tests were applied to the spectral data to calculate significant spectral differences and between which pairs of rocks these significant differences occurred. Results showed that there were significant spectral differences between all the rock types of the Mambulu Complex. The variability of spectral characteristics within rock species was attributed to the difference in composition of fresh and weathered surfaces; and the significant spectral differences between rock samples can be attributed primarily to differences in mineral composition. / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2012.

A Charge Injection Device (CID) detector has been evaluated as a detector for simultaneous multielement atomic emission spectroscopy. The CID was incorporated into a special liquid nitrogen cooled, computer controlled camera system. Electro-optical characterization of the CID and camera system included determination of readout noise, quantum efficiency, spatial crosstalk, temporal hysteresis, spatial response uniformity, and linear dynamic range. The CID was used as a spectroscopic detector for an echelle grating spectrometer equipped with a direct current plasma emission source. The spectrometer was a standard commercial instrument modified to provide a reduced image format more suitable for use with the CID detector. The optical characteristics of this spectrometer, including wavelength coverage, and optical aberrations are described. The spectroscopic system was evaluated with respect to detection limits, linear dynamic range, and accuracy in both single element and simultaneous multielement modes. Detection limits compared well to literature values reported for photomultiplier tube detector based systems under similar conditions. CID detection limits were superior in the near infrared and visible wavelength region, comparable in the middle UV, and higher in the far UV. The detection limits were determined to be limited by background radiation shot noise. Several elements of a certified standard reference material were simultaneously determined in order to assess the accuracy of the spectroscopic system. The results were highly accurate, even when operating near or below the 3σ limits of detection. Spectral interferences for elements were avoided by using several analytical lines for each element. The results of these investigations indicate that the CID is a superior multichannel detector for analytical atomic emission spectrometry. The capability to simultaneously monitor a wide, continuous spectral range with high spatial resolution, high dynamic range, low readout noise, and insignificant signal crosstalk is now possible. Many analytical benefits of this approach, such as the potential capability to perform rapid qualitative and semiquantitative analysis and the ability to select the optimum spectral lines for highly accurate quantitative analysis are now readily achievable.

<p align="justify">L'étude des phénomènes physico-chimiques de l'atmosphère nécessite la connaissance préalable des caractéristiques de chacun de ses constituants, ainsi que de leurs distributions spatiales et temporelles. Les méthodes spectroscopiques permettent la détection simultanée de nombreux constituants atmosphériques par la mesure quantitative de leurs absorptions. Dans le domaine UV-visible, ces techniques se basent sur la loi de Beer-Lambert, dont l'application nécessite la connaissance d'un spectre de référence exempt d'absorption. Il est impossible d'obtenir un tel spectre dans le cas des mesures atmosphériques. On a alors recourt à la technique dite de spectroscopie d'absorption différentielle (Differential Optical Absorption Spectroscopy) qui analyse les composantes des absorptions variant rapidement en fonction de la longueur d'onde.</p><p><p align="justify">Trois instruments ont été développés dans le cadre de ce travail pour la mesure par spectroscopie d'absorption différentielle dans le domaine UV-visible. Le premier utilise un spectromètre par transformée de Fourier, les deux autres des spectromètres à réseau associés soit à une barrette de photodiodes soit à un détecteur de type CCD. Ces instruments ont été conçus dans le but de fournir des mesures de divers constituants (03, SO2, NO2, HNO2, H2CO, toluène, benzène) de manière automatique et en utilisant des trajets d'absorption courts ( < 1 km). Les performances de chacun de ces instruments ont été évaluées au cours de différentes campagnes de mesure. Le spectromètre par transformée de Fourier s'avère être un outil performant pour de telles mesures, son principal avantage étant de posséder une calibration en longueur d'onde interne, précise et reproductible. Les instruments utilisant un spectromètre à réseau associé à un détecteur multi-éléments présentent un certain nombre d'inconvénients rendant peu aisées les mesures troposphériques sur de courtes distances. Ces inconvénients sont liés soit au spectromètre ( calibration en longueur d'onde externe, modification de celle-ci au cours du temps) ou aux détecteurs ( gains différents pour chacun des éléments sensibles du détecteur, phénomènes d'interférence au niveau des fenêtres de protection). Ces problèmes augmentent la complexité de l'analyse des spectres atmosphériques.</p><p><p align="justify">Un paramètre d'importance primordiale pour la détection d'un polluant, est sa section efficace d'absorption. Nous avons mesuré la section efficace de trois molécules d'intérêt atmosphérique, SO2, CS2 et NO2. Ces spectres ont été obtenus à l'aide d'un spectromètre par transformée de Fourier, aux résolutions de 2 et 16 cm-1. La dépendance vis-à-vis de la température a été confirmée dans le cas du NO2. Pour cette molécule, un effet de pression a en outre été observé pour la première fois dans le domaine spectral 12000 20000 cm-1 (500-830 nm). Cet effet est important et peut engendrer des variations de 45% de l'intensité de la section efficace lorsque la pression partielle de NO2 varie de 0.02 à 1.0 torr. L'influence du choix des sections efficaces sur les mesures stratosphériques de NO2 a également été mise en évidence. L'utilisation de sections efficaces obtenue à basse température (220 K) implique une diminution de 20% de la quantité de NO2 mesurée mais également une diminution de l'erreur sur cette mesure. Ceci indique la nécessité de tenir compte de la dépendance des sections efficaces de NO2 à la température lors de l'analyse de spectres stratosphériques.</p><p><p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished