Masters Theses
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Browsing Masters Theses by Department "Analytical Chemistry"
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- The analysis of the gaseous portions of the volatile matter of Virginia coals given off or released at several different temperaturesPrice, Nelson O. (Virginia Agricultural and Mechanical College and Polytechnic Institute, 1931)Due to many unexpected difficulties which developed as the method was being worked out, all of the desired information on these coals was not obtained. Therefore, most of the allotted time has to be devoted to the standardizing of the apparatus. Many of the small but important points of technique, which gave trouble, have been overcome.
- The evaluation of a low powered microwave induced plasma as an atom cell for atomic spectrometryPerkins, Larry D. (Virginia Tech, 1987-05-15)The range of plasma spectroscopy tends to increase with the introduction of more efficient plasma excitation sources. In this thesis the use of one such plasma excitation source, the microwave induced plasma is evaluated as an atom cell for atomic spectrometry. The modes of spectrometry evaluated are atomic emission and atomic fluoresence. Analytical merits of the microwave induced plasma using detection limits and studies of interelement effects (i.e. vaporization, ionizationâ and scatter interferences) are also presented.
- LC - ¹³C NMR utilizing dynamic nuclear polarization (DNP) for signal enhancementStevenson, Steven A. (Virginia Tech, 1992-06-05)The primary difficulty for successful LC - ¹³C NMR (whether ¹H or ¹³C) is overcoming the relatively low sensitivity of NHR as a chromatographic detector. For the ¹H nuclide this is much less of a problem; the sensitivity ;s approximately 6000 times more sensitive than that of ¹³C nuclei. For this reason, much of the literature focuses on LC - ¹H NMR. To ever successfully realize LC - ¹³C NMR, it is mandatory that an augmentation of ¹³C signal intensity must be effectuated to overcome this sensitivity deficit (~ three orders of magnitude). To satisfy this requirement, our laboratory has utilized dynamic nuclear polarization (DNP) to ameliorate these otherwise weak or non-existent signals. For favorable molecules, sensitivity recoveries of up to two orders of magnitude have been developed. This improvement (relative to 'H) narrows the sensitivity gap between 'H and ¹³C NMR detection of chromatographically separated analytes. Despite the fact that relatively large injection volumes were required in most LC experiments, the wealth of structural information inherent to ¹³C NMR justifies any attempt to successfully couple nuclear magnetic resonance to liquid chromatography. In addition, DNP was utilized in a series of SLIT and LLIT experiments where a test mixture was recycled through a NMR spectrometer. Results indicate that ¹³C spectra were obtained with a significantly higher signal-to-noise ratio in a shorter amount of analysis time relative to experiments where DNP was not employed for signal enhancement.
- Quantitative analysis of rocket propellant by capillary gas chromatographySotack, Gregg S. (Virginia Tech, 1988)The analysis of nitrate-ester propellants and explosives has been performed extensively by gas chromatography for the past decade. As capillary GC technology has advanced, new opportunities for the improvement of existing methods have developed. This investigation probes several of these possibilities. The effect on quantitation of: the solvent, the analysis time, and the use of splitless injection were investigated. Precision was shown to be improved by: 1. using a non-volatile solvent (toluene) rather than CH₂Cl₂, 2. using the most time-efficient method that will allow adequate resolution of the components, 3. using splitless injection (0.80 min. splitless time). After these potential improvements of method were investigated, the mechanism employed in splitless injection was investigated. This mechanism is known as the SOLVENT EFFECT. The investigation showed that: 1. non-volatile components required less splitless time to achieve 100% sample transfer to the column; 2. using splitless injection improved precision over split injection; 3. injector liner design had no effect on precision; 4. column overload did not hurt precision, as long as all peaks remain baseline-resolved; 5. the initial column temperature must be below the boiling point of the solvent (how far below did not appear to be very significant); 6. quantitation is improved by using a solvent that is as non-volatile as possible; 7. varying the split ratio after the split vent has reopened (within the range of 20:1 to 500:1) has no effect on resolving peaks that occur extremely close to the solvent peak.
- The use of a microchannel plate in the development of a chemical sensorSchechter, Michael L. (Virginia Tech, 1991)The use of a microchannel plate as an optical encoding device has many advantages. These include large surface area and large-scale signal averaging. This instrument was designed to obtain and interpret the information generated by the optical transform of a microchannel plate. It will be shown that a large amount of information about solution interactions and properties can be obtained from such an instrument.