+publisher:"Virginia Tech" +contributor:("Glanville, James O.")

Virginia Tech

1. Brannegan, Daniel Robert. Analysis of Ethoxyquin and its Oxidation Products using Supercritical Fluid Extraction and High Performance Liquid Chromatography with Chemiluminescent Nitrogen Detection.

Degree: MS, Chemistry, 2000, Virginia Tech

URL: http://hdl.handle.net/10919/31575

► Ethoxyquin is an antioxidant commonly used to preserve vitamins and lipids in various food products and animal feeds. The extraction and determination of ethoxyquin is… (more)

▼ Ethoxyquin is an antioxidant commonly used to preserve vitamins and lipids in various food products and animal feeds. The extraction and determination of ethoxyquin is becoming increasingly important as products, which are labeled as "natural" are becoming more common. The present method of determination only ensures that ethoxyquin values are below 10-20 parts per million. Therefore, advances are needed in methods of extraction and analysis in order to lower the detection limits in various products. The first part of this research investigates the use of supercritical fluids in the extraction of ethoxyquin from lean beef and beef fat. Supercritical fluids offer the advantages of safety, time, expense, and selectivity over liquid extractions. Three fluids were examined: carbon dioxide, trifluoromethane, and 1,1,1,2-tetrafluoroethane. Carbon dioxide appeared to react with ethoxyquin during the extraction. Methanol modified hydrofluorocarbons provided more complete extractions over pure hydrofluorocarbon fluids. Methanol modified 1,1,1,2-tetrafluoroethane was used in the extraction of ethoxyquin from lean beef and beef fat, and provided a quantitative extraction at the 0.5 ppm level. The second part of this research centered on the separation and quantitation of the oxidation products of ethoxyquin through the use of high pressure liquid chromatography with chemiluminescence nitrogen detection (HPLC/CLND). When ethoxyquin is oxidized, the resulting products also exhibit antioxidative properties. While these oxidation products are known, no effort has been made to separate and quantify them in real or clean samples. HPLC/CLND allows all nitrogen containing compounds to be quantified without a known standard. This method is of extreme interest in the case of ethoxyquin oxidation products, or other types of metabolites, where standards are difficult to obtain or are unstable. HPLC/CLND allowed a separation of ethoxyquin and four of its oxidation products to be detected, thus making future studies of the antioxidant behavior of ethoxyquin feasible. Advisors/Committee Members: Taylor, Larry T. (committeechair), Glanville, James O. (committee member), McNair, Harold M. (committee member).

Subjects/Keywords: Oxidation; SFC; Extraction; Ethoxyquin; Chromatography; GC/MS; Supercritical; HPLC/CLND; Beef; HPLC; Beef Fat

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APA (6^th Edition):

Brannegan, D. R. (2000). Analysis of Ethoxyquin and its Oxidation Products using Supercritical Fluid Extraction and High Performance Liquid Chromatography with Chemiluminescent Nitrogen Detection. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/31575

Chicago Manual of Style (16^th Edition):

Brannegan, Daniel Robert. “Analysis of Ethoxyquin and its Oxidation Products using Supercritical Fluid Extraction and High Performance Liquid Chromatography with Chemiluminescent Nitrogen Detection.” 2000. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/31575.

MLA Handbook (7^th Edition):

Brannegan, Daniel Robert. “Analysis of Ethoxyquin and its Oxidation Products using Supercritical Fluid Extraction and High Performance Liquid Chromatography with Chemiluminescent Nitrogen Detection.” 2000. Web. 18 Jan 2021.

Vancouver:

Brannegan DR. Analysis of Ethoxyquin and its Oxidation Products using Supercritical Fluid Extraction and High Performance Liquid Chromatography with Chemiluminescent Nitrogen Detection. [Internet] [Masters thesis]. Virginia Tech; 2000. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/31575.

Council of Science Editors:

Brannegan DR. Analysis of Ethoxyquin and its Oxidation Products using Supercritical Fluid Extraction and High Performance Liquid Chromatography with Chemiluminescent Nitrogen Detection. [Masters Thesis]. Virginia Tech; 2000. Available from: http://hdl.handle.net/10919/31575

Virginia Tech

2. Schneider, Mark S. Analysis of Organic Pollutants by Micro Scale Liquid-Liquid Extraction and On-column Large Volume Injection Gas Chromatography.

Degree: MS, Chemistry, 1998, Virginia Tech

URL: http://hdl.handle.net/10919/46329

► The analysis of organic pollutants in water is traditionally done following EPA procedures which commonly use liquid-liquid extraction. One liter of water is extracted three… (more)

Subjects/Keywords: Large Volume Injection; Water Analysis; Micro Scale Extraction; Oganic Pollutants

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APA (6^th Edition):

Schneider, M. S. (1998). Analysis of Organic Pollutants by Micro Scale Liquid-Liquid Extraction and On-column Large Volume Injection Gas Chromatography. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/46329

Chicago Manual of Style (16^th Edition):

Schneider, Mark S. “Analysis of Organic Pollutants by Micro Scale Liquid-Liquid Extraction and On-column Large Volume Injection Gas Chromatography.” 1998. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/46329.

MLA Handbook (7^th Edition):

Schneider, Mark S. “Analysis of Organic Pollutants by Micro Scale Liquid-Liquid Extraction and On-column Large Volume Injection Gas Chromatography.” 1998. Web. 18 Jan 2021.

Vancouver:

Schneider MS. Analysis of Organic Pollutants by Micro Scale Liquid-Liquid Extraction and On-column Large Volume Injection Gas Chromatography. [Internet] [Masters thesis]. Virginia Tech; 1998. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/46329.

Council of Science Editors:

Schneider MS. Analysis of Organic Pollutants by Micro Scale Liquid-Liquid Extraction and On-column Large Volume Injection Gas Chromatography. [Masters Thesis]. Virginia Tech; 1998. Available from: http://hdl.handle.net/10919/46329

Virginia Tech

3. Gillmore, Jason G. Jr. Evaluation of 1,1-Dimethyl-5,7-Di-T-Butylspiro[2.5]Octa-4,7-Dien-6-One as a Mechanistic Probe for Single Electron Transfer.

Degree: MS, Chemistry, 1998, Virginia Tech

URL: http://hdl.handle.net/10919/36888

► Single electron transfer (SET) mechanisms are becoming ubiquitous in modern organic chemistry. However, it is often difficult to distinguish SET mechanisms from polar mechanisms.… (more)

Subjects/Keywords: Grignard reagents; SET; Radical anions; Ketyl anion

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APA (6^th Edition):

Gillmore, J. G. J. (1998). Evaluation of 1,1-Dimethyl-5,7-Di-T-Butylspiro[2.5]Octa-4,7-Dien-6-One as a Mechanistic Probe for Single Electron Transfer. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/36888

Chicago Manual of Style (16^th Edition):

Gillmore, Jason G Jr. “Evaluation of 1,1-Dimethyl-5,7-Di-T-Butylspiro[2.5]Octa-4,7-Dien-6-One as a Mechanistic Probe for Single Electron Transfer.” 1998. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/36888.

MLA Handbook (7^th Edition):

Gillmore, Jason G Jr. “Evaluation of 1,1-Dimethyl-5,7-Di-T-Butylspiro[2.5]Octa-4,7-Dien-6-One as a Mechanistic Probe for Single Electron Transfer.” 1998. Web. 18 Jan 2021.

Vancouver:

Gillmore JGJ. Evaluation of 1,1-Dimethyl-5,7-Di-T-Butylspiro[2.5]Octa-4,7-Dien-6-One as a Mechanistic Probe for Single Electron Transfer. [Internet] [Masters thesis]. Virginia Tech; 1998. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/36888.

Council of Science Editors:

Gillmore JGJ. Evaluation of 1,1-Dimethyl-5,7-Di-T-Butylspiro[2.5]Octa-4,7-Dien-6-One as a Mechanistic Probe for Single Electron Transfer. [Masters Thesis]. Virginia Tech; 1998. Available from: http://hdl.handle.net/10919/36888

Virginia Tech

4. Song, Xiling. Analysis of Aroma Constituents in Cultivated Strawberries by GC/MS.

Degree: MS, Chemistry, 1999, Virginia Tech

URL: http://hdl.handle.net/10919/42874

► In aroma analysis, strawberries have always been the favored fruit because of their relatively high content of typical and pleasant aroma constituents. Esters, aldehydes, alcohols… (more)

▼ In aroma analysis, strawberries have always been the favored fruit because of their relatively high content of typical and pleasant aroma constituents. Esters, aldehydes, alcohols and sulfur compounds have been found to be the main aroma components in strawberry. In recent years, two volatile compounds, 2,5-dimethyl-4-methoxy-3(2H)-furanone (DMF) and 2,5-dimethyl-4-hydroxy-3(2H)-furanone (DHF) were reported to contribute heavily to strawberry aroma. These two compounds have been found in all wild strawberries studied, but found only in few cultivated varieties. In this work, three kinds of cultivated strawberries were sampled and analyzed. The three strawberries all belong to the Camarosa variety. They came from different growing areas: Salinas (California), Orrville (Ohio), and Memphis (Tennessee). The volatile compounds of these three strawberries were separated by Gas Chromatography (GC), and identified by Mass Spectrometer Detector (MSD). Column and experimental conditions were optimized for this particular separation. Salinas, Orrville and Memphis strawberries have very similar aroma constituents, however, in slightly differing amounts. Several unique peaks were found in each strawberry, which may well account for the differences in the aroma qualities of the three. 2-Furaldehyde was found in both Memphis and Orrville strawberries, but not in Salinas. It is a key odor compound correlated with woody aroma and it has a low odor threshold value. These two properties make it contribute negatively to the pleasant aroma of Memphis and Orrville strawberries. A compound, 2-furanmethanol, was found only in Salinas strawberries. This compound has a faint burning aroma, however, its high odor threshold value offsets its potentially bad aroma. DMF was found in all three strawberries, but no DHF was detected in any of the three. We propose a possible explanation for the absence of DHF. Ethyl (methylthio) acetate, which is a sulfur-containing compound, was found in both Orrville and Salinas strawberries. This work is the first to report its presence in strawberries of any variety. An external standard method was employed to quantify seven main aroma components found in the strawberry extracts. Aroma values were introduced and then calculated together with sensory descriptions of these compounds. Salinas strawberry was found to have the best aroma quality of the three. These results indicate that the odors of strawberries of the same variety can be different when grown in different geographical areas. Advisors/Committee Members: Glanville, James O. (committee member), Taylor, Larry T. (committee member), McNair, Harold M. (committee member).

Subjects/Keywords: Aroma Value; Camarosa strawberries; GC/MS

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APA (6^th Edition):

Song, X. (1999). Analysis of Aroma Constituents in Cultivated Strawberries by GC/MS. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/42874

Chicago Manual of Style (16^th Edition):

Song, Xiling. “Analysis of Aroma Constituents in Cultivated Strawberries by GC/MS.” 1999. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/42874.

MLA Handbook (7^th Edition):

Song, Xiling. “Analysis of Aroma Constituents in Cultivated Strawberries by GC/MS.” 1999. Web. 18 Jan 2021.

Vancouver:

Song X. Analysis of Aroma Constituents in Cultivated Strawberries by GC/MS. [Internet] [Masters thesis]. Virginia Tech; 1999. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/42874.

Council of Science Editors:

Song X. Analysis of Aroma Constituents in Cultivated Strawberries by GC/MS. [Masters Thesis]. Virginia Tech; 1999. Available from: http://hdl.handle.net/10919/42874

Virginia Tech

5. Thompson, Peter G. Liquid collection efficiencies after supercritical fluid extraction.

Degree: MS, Chemistry, 1994, Virginia Tech

URL: http://hdl.handle.net/10919/44469

Subjects/Keywords: Supercritical fluid extraction; LD5655.V855 1994.T5667

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APA (6^th Edition):

Thompson, P. G. (1994). Liquid collection efficiencies after supercritical fluid extraction. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/44469

Chicago Manual of Style (16^th Edition):

Thompson, Peter G. “Liquid collection efficiencies after supercritical fluid extraction.” 1994. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/44469.

MLA Handbook (7^th Edition):

Thompson, Peter G. “Liquid collection efficiencies after supercritical fluid extraction.” 1994. Web. 18 Jan 2021.

Vancouver:

Thompson PG. Liquid collection efficiencies after supercritical fluid extraction. [Internet] [Masters thesis]. Virginia Tech; 1994. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/44469.

Council of Science Editors:

Thompson PG. Liquid collection efficiencies after supercritical fluid extraction. [Masters Thesis]. Virginia Tech; 1994. Available from: http://hdl.handle.net/10919/44469

Virginia Tech

6. Pinto, Angela Marie III. Quantitative Analysis of Antioxidants from High Density Polyethylene (HDPE) by off-line Supercritical Fluid Extraction Coupled High Performance Liquid Chromatography.

Degree: MS, Chemistry, 1997, Virginia Tech

URL: http://hdl.handle.net/10919/36932

► Plastics are widely used and they vary in their applicability, ranging from automobile parts, components for houses and buildings, and packaging for everything from food… (more)

▼ Plastics are widely used and they vary in their applicability, ranging from automobile parts, components for houses and buildings, and packaging for everything from food to electronic parts. The diverse applications of plastics, such as polystyrene, polyolefins and polyester, are credited to the incorporation of additives. Additives improve the performance of these and other polymer resins. Without the incorporation of such additives, for example Ethanox Â® 330, some plastics would degrade during processing or over time. To ensure that the specified amount of an additive or combination of additives are incorporated into a polymer after the extrusion process, a rapid and accurate analytical method is required. Quantitation of additive(s) in the polymer is necessary, since the additive(s) may degrade and the amount of additive(s) can influence the physical nature of the polymer. Conventional extraction techniques for polymer additive(s), such as, Soxhlet or dissolution / precipitation are labor intensive, time consuming, expensive, and the optimal recovery is significantly less than 90 percent. In addition, a large amount of solvent , such as toluene or decalin, must be eliminated in order to concentrate the sample prior to chromatographic separation. Supercritical Fluid Extraction (SFE) has been employed as an alternative polymer preparation technique. SFE is a favorable means for various analytical sample preparation applications, credited to its short extraction times. This research employs SFE for the extraction of the antioxidant EthanoxÂ® 330 from high density polyethylene (HDPE) followed by HPLC/UV analysis. The effects of temperature, modifier type, and modifier concentration were investigated. Once the optimal extraction conditions were determined, the extraction efficiency of Ethanox Â® 330 as a single additive and in the presence of co-additives from HDPE were investigated. Recoveries of greater than 90% were obtained for Ethanox Â® 330 when a secondary antioxidant was present in the HDPE. Advisors/Committee Members: Taylor, Larry T. (committeechair), Ward, Thomas C. (committee member), Wolfe, James F. (committee member), Glanville, James O. (committee member).

Subjects/Keywords: SFE; Ethanox Â® 398; Ethanox Â® 330; Extraction; High Density Polyethylene (HDPE); Supercritical; Mass Spectrometry; HPLC; Direct-Inlet Probe (DIP)

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APA (6^th Edition):

Pinto, A. M. I. (1997). Quantitative Analysis of Antioxidants from High Density Polyethylene (HDPE) by off-line Supercritical Fluid Extraction Coupled High Performance Liquid Chromatography. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/36932

Chicago Manual of Style (16^th Edition):

Pinto, Angela Marie III. “Quantitative Analysis of Antioxidants from High Density Polyethylene (HDPE) by off-line Supercritical Fluid Extraction Coupled High Performance Liquid Chromatography.” 1997. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/36932.

MLA Handbook (7^th Edition):

Pinto, Angela Marie III. “Quantitative Analysis of Antioxidants from High Density Polyethylene (HDPE) by off-line Supercritical Fluid Extraction Coupled High Performance Liquid Chromatography.” 1997. Web. 18 Jan 2021.

Vancouver:

Pinto AMI. Quantitative Analysis of Antioxidants from High Density Polyethylene (HDPE) by off-line Supercritical Fluid Extraction Coupled High Performance Liquid Chromatography. [Internet] [Masters thesis]. Virginia Tech; 1997. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/36932.

Council of Science Editors:

Pinto AMI. Quantitative Analysis of Antioxidants from High Density Polyethylene (HDPE) by off-line Supercritical Fluid Extraction Coupled High Performance Liquid Chromatography. [Masters Thesis]. Virginia Tech; 1997. Available from: http://hdl.handle.net/10919/36932

Virginia Tech

7. Henry, Mark B. Rapid analysis of chloride content of contaminated concrete.

Degree: MS, Civil Engineering, 1992, Virginia Tech

URL: http://hdl.handle.net/10919/41803

► In 1989, the specific ion electrode was identified as the best field method available to assess the chloride content of powdered concrete samples. Since the… (more)

Subjects/Keywords: Chlorides; LD5655.V855 1992.H467

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APA (6^th Edition):

Henry, M. B. (1992). Rapid analysis of chloride content of contaminated concrete. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/41803

Chicago Manual of Style (16^th Edition):

Henry, Mark B. “Rapid analysis of chloride content of contaminated concrete.” 1992. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/41803.

MLA Handbook (7^th Edition):

Henry, Mark B. “Rapid analysis of chloride content of contaminated concrete.” 1992. Web. 18 Jan 2021.

Vancouver:

Henry MB. Rapid analysis of chloride content of contaminated concrete. [Internet] [Masters thesis]. Virginia Tech; 1992. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/41803.

Council of Science Editors:

Henry MB. Rapid analysis of chloride content of contaminated concrete. [Masters Thesis]. Virginia Tech; 1992. Available from: http://hdl.handle.net/10919/41803

Virginia Tech

8. Eddleton, Jeannine E. Chemical demonstrations: a compendium of resources in print and on the Internet.

Degree: MS, Chemistry, 1996, Virginia Tech

URL: http://hdl.handle.net/10919/45839

► This masters report pulls together the body of resources available to assist the lecture demonstrator. professor. and teacher of chemistry in incorporating the very… (more)

Subjects/Keywords: chemistry; chemical; experiments; lecture; demonstrations; laboratory; LD5655.V855 1996.E335

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APA (6^th Edition):

Eddleton, J. E. (1996). Chemical demonstrations: a compendium of resources in print and on the Internet. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/45839

Chicago Manual of Style (16^th Edition):

Eddleton, Jeannine E. “Chemical demonstrations: a compendium of resources in print and on the Internet.” 1996. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/45839.

MLA Handbook (7^th Edition):

Eddleton, Jeannine E. “Chemical demonstrations: a compendium of resources in print and on the Internet.” 1996. Web. 18 Jan 2021.

Vancouver:

Eddleton JE. Chemical demonstrations: a compendium of resources in print and on the Internet. [Internet] [Masters thesis]. Virginia Tech; 1996. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/45839.

Council of Science Editors:

Eddleton JE. Chemical demonstrations: a compendium of resources in print and on the Internet. [Masters Thesis]. Virginia Tech; 1996. Available from: http://hdl.handle.net/10919/45839

Virginia Tech

9. Heng, Kien Chhiev. Effect of column temperature on elution order in gas chromatography.

Degree: MS, Chemistry, 1994, Virginia Tech

URL: http://hdl.handle.net/10919/40864

► This study concerns the effect of column temperature on selectivity in gas chromatography (GC). Reversal of peak elution order at different temperatures is observed when… (more)

▼ This study concerns the effect of column temperature on selectivity in gas chromatography (GC). Reversal of peak elution order at different temperatures is observed when selectivity is sufficiently changed by changing the temperature. A study of homologous functional groups and the elution order of a test mixture was made at several temperatures, by keeping constant operating chromatographic parameters such as column head pressure, split ratio, sample concentration, injector and detector temperature. The homologous series studied were esters, carboxylic acids, ketones and alkanes. The stationary phases used were Carbowax (Supelcowax 10), and 5% diphenyl and 95% dimethyl silicone ( HP Ultra 2). The identification of each compound was confirmed by two methods : comparing retention times, and spiking the sample. The results of an investigation for accurately determining the dead time is also presented. The experimental results of using 10% methane in helium and the results of a theoretical model based on Poiseuille' s equation were studied and compared. It is concluded that dead time calculations are a major source of error for the calculations in this work. In addition, a derived thermodynamic equation based on the Van't Hoff equation was obtained and used to calculate the molar enthalpy and entropy of compounds over a range of temperatures. The experimental thermodynamic values were compared with the theoretical values obtained from the Clausius- Clapeyron equation. From the data obtained, a graph of In k' (retention factor) versus 1/ temperature for a homologous series, known as a Van't Hoff plot, predicts a reversal of elution order where an intersection of two lines occur. Selectivity of the stationary phase has changed solely due to temperature effects. This can only occur when different solute/solvent interactions are present. This work is an attempt to predict when peak inversion should occur based on the Van Hoff's plot. Experimental result are presented that confirm the prediction. Advisors/Committee Members: McNair, Harold M. (committeechair), Glanville, James O. (committee member), Viers, Jimmy W. (committee member), Hinshaw, J. V. Jr. (committee member).

Subjects/Keywords: Gas chromatography; LD5655.V855 1994.H464

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APA (6^th Edition):

Heng, K. C. (1994). Effect of column temperature on elution order in gas chromatography. (Masters Thesis). Virginia Tech. Retrieved from http://hdl.handle.net/10919/40864

Chicago Manual of Style (16^th Edition):

Heng, Kien Chhiev. “Effect of column temperature on elution order in gas chromatography.” 1994. Masters Thesis, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/40864.

MLA Handbook (7^th Edition):

Heng, Kien Chhiev. “Effect of column temperature on elution order in gas chromatography.” 1994. Web. 18 Jan 2021.

Vancouver:

Heng KC. Effect of column temperature on elution order in gas chromatography. [Internet] [Masters thesis]. Virginia Tech; 1994. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/40864.

Council of Science Editors:

Heng KC. Effect of column temperature on elution order in gas chromatography. [Masters Thesis]. Virginia Tech; 1994. Available from: http://hdl.handle.net/10919/40864

Virginia Tech

10. Subramaniam, Chitra P. Morphology, Crystallization and Melting Behaviors of Random Copolymers of Ethylene with 1-Butene, 1-Pentene and 1-Hexene.

Degree: PhD, Chemistry, 1999, Virginia Tech

URL: http://hdl.handle.net/10919/28064

► The morphology, crystallization and melting behaviors of a series of ethylene/alpha-olefin copolymers were investigated as a function of comonomer content, comonomer type and processing conditions,… (more)

▼ The morphology, crystallization and melting behaviors of a series of ethylene/alpha-olefin copolymers were investigated as a function of comonomer content, comonomer type and processing conditions, including crystallization temperature and time. This was achieved by using a combination of techniques such as Nuclear Magnetic Resonance Spectroscopy (NMR), Differential Scanning Calorimetry (DSC), Atomic Force Microscopy (AFM) and Fourier Transform Infrared Spectroscopy (FTIR). The results from the thermal analysis studies clearly indicated the existence of two distinct regions of crystallization, demarcated by a cross-over temperature, 𝑇*. The high temperature region (above 𝑇*) displayed cooling-rate dependence as well as significant hysteresis in crystallinity between cooling and heating processes, similar to that observed in linear polyethylene. This implied that the crystals associated with this region were formed via chain-folded lamellar growth. However, the lower temperature region (below 𝑇*) exhibited reversible changes in crystallinity between cooling and heating, and was found to be independent of the cooling rate. The temporal evolution of secondary crystallization in the copolymers was studied for times ranging from 100-106 min, at different crystallization temperatures (Tx). Two distinct melting endotherms were discerned at crystallization temperatures below 𝑇*. A higher melting endotherm that remained invariant with crystallization time (tx) was associated with lamellar crystals that were formed during primary crystallization. In contrast, both the positions as well as the magnitude of the lower temperature endotherm were found to vary systematically with log (tx). The peak positions of the low endotherm, i.e., the melting temperature of the secondary crystals, were found to consistently extrapolate to the crystallization temperature at very short times. Based on this and other considerations, the secondary crystals were associated with the melting of thin stacks of polymer chains aggregated in the form of "fringed-micelle"-like bundled crystals. The temperature dependence of the kinetic parameters (derived from Avrami and other analyses) above 𝑇* and their invariance below 𝑇*, suggested that the transformation in morphology from lamellar to bundled crystals was gradual and systematic, as the branch content was increased or as the crystallization temperature was lowered. Further verification of this result was obtained via AFM experiments. A systematic variation in morphology from lamellar to spot-like (lamellae were less clearly visible) was clearly discerned on increasing the comonomer content. Furthermore, a second morphological feature represented by bridge-like links between the lamellae, and approximately perpendicular to them, was also observed for some copolymers. This feature was correlated with the bundled crystals discussed above. The presence of an alternate crystal structure, in addition to the usual orthorhombic crystal form expected for linear polyethylene, was also established from the… Advisors/Committee Members: Marand, Hervé L. (committeechair), Wilkes, Garth L. (committee member), Ward, Thomas C. (committee member), Gibson, Harry W. (committee member), Glanville, James O. (committee member).

Subjects/Keywords: Secondary Crystallization; Ethlyene/alpha-olefin copolymers; Random copolymers; Morphology; Structure

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APA (6^th Edition):

Subramaniam, C. P. (1999). Morphology, Crystallization and Melting Behaviors of Random Copolymers of Ethylene with 1-Butene, 1-Pentene and 1-Hexene. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/28064

Chicago Manual of Style (16^th Edition):

Subramaniam, Chitra P. “Morphology, Crystallization and Melting Behaviors of Random Copolymers of Ethylene with 1-Butene, 1-Pentene and 1-Hexene.” 1999. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/28064.

MLA Handbook (7^th Edition):

Subramaniam, Chitra P. “Morphology, Crystallization and Melting Behaviors of Random Copolymers of Ethylene with 1-Butene, 1-Pentene and 1-Hexene.” 1999. Web. 18 Jan 2021.

Vancouver:

Subramaniam CP. Morphology, Crystallization and Melting Behaviors of Random Copolymers of Ethylene with 1-Butene, 1-Pentene and 1-Hexene. [Internet] [Doctoral dissertation]. Virginia Tech; 1999. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/28064.

Council of Science Editors:

Subramaniam CP. Morphology, Crystallization and Melting Behaviors of Random Copolymers of Ethylene with 1-Butene, 1-Pentene and 1-Hexene. [Doctoral Dissertation]. Virginia Tech; 1999. Available from: http://hdl.handle.net/10919/28064

Virginia Tech

11. McDaniel, Lori Heldreth. Investigation of Liquid Trapping Following Supercritical Fluid Extraction.

Degree: PhD, Chemistry, 1999, Virginia Tech

URL: http://hdl.handle.net/10919/29121

► Supercritical fluid extraction (SFE) is an alternative to traditional extractions with organic solvents. SFE consists of removing the analyte(s) from the matrix, solubilizing them, moving… (more)

▼ Supercritical fluid extraction (SFE) is an alternative to traditional extractions with organic solvents. SFE consists of removing the analyte(s) from the matrix, solubilizing them, moving the analyte(s) into the bulk fluid, and sweeping the fluid containing the analyte(s) out of the extraction vessel. As the fluid leaves the extraction vessel, decompression of the fluid occurs, changing its volume and temperature which can lead to analyte loss. This work focussed on the trapping process with the restrictor immersed in a liquid after SFE. Experiments compared the effects of trapping parameters on the collection efficiencies of fat-soluble vitamins of similar polarities and structures. The most important variable was the selection of collection solvent and its physical properties, such as viscosity, surface tension and density were found to be important. Additionally, adding a modifier to the collection solvent in an attempt to change its physical properties and influence collection efficiencies for a polarity test mix was studied. Addition of a modifier can improve collection efficiencies and allow higher collection temperature to be used, but the modifier did not increase trapping recoveries to the extent that collection pressurization did. The occurrence of a methylation reaction of decanoic acid during the SFE and collection processes, using a methanol modified fluid or collection solvent was investigated. The majority of the reaction occurred during the collection process and the degree of methylation was found to be dependent on temperature, but not on static or dynamic extraction time. When no additional acidic catalyst other than carbon dioxide in the presence of water was present, conversion was limited to about 2%, but was quantitative with an added acidic catalyst. The last portion of this work involved the application of the SFE process to the extraction and analysis of extractable material in eight hardwood and softwood pulp samples. Grinding the samples increased extractable fatty acid methyl esters (FAMEs) by ten-fold, and in-situ derivatizations resulted in higher FAME recoveries than derivatization after SFE. Liquid trapping enhanced recoveries of lower FAMEs when compared to tandem (solid/liquid) trapping. In-situ acetylations sometimes yielded acetylated glucoses. Large differences in FAMEs concentrations were seen for hardwood samples, but lesser differences were seen for the softwood pulp samples. Advisors/Committee Members: Taylor, Larry T. (committeechair), Long, Gary L. (committee member), Bell, Harold M. (committee member), Glanville, James O. (committee member), McNair, Harold M. (committee member).

Subjects/Keywords: collection solvent modification; supercritical fluid extraction; liquid trapping; fat-soluble vitamins; in-situ methylation; wood pulp

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APA (6^th Edition):

McDaniel, L. H. (1999). Investigation of Liquid Trapping Following Supercritical Fluid Extraction. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/29121

Chicago Manual of Style (16^th Edition):

McDaniel, Lori Heldreth. “Investigation of Liquid Trapping Following Supercritical Fluid Extraction.” 1999. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/29121.

MLA Handbook (7^th Edition):

McDaniel, Lori Heldreth. “Investigation of Liquid Trapping Following Supercritical Fluid Extraction.” 1999. Web. 18 Jan 2021.

Vancouver:

McDaniel LH. Investigation of Liquid Trapping Following Supercritical Fluid Extraction. [Internet] [Doctoral dissertation]. Virginia Tech; 1999. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/29121.

Council of Science Editors:

McDaniel LH. Investigation of Liquid Trapping Following Supercritical Fluid Extraction. [Doctoral Dissertation]. Virginia Tech; 1999. Available from: http://hdl.handle.net/10919/29121

Virginia Tech

12. Goebel, Lisa Karen. Electrokinetic separations involving surfactants and proteins.

Degree: PhD, Chemistry, 1992, Virginia Tech

URL: http://hdl.handle.net/10919/39443

► Methods for the analysis of surfactants and proteins by Capillary Electrophoresis (CE) were investigated. Several modifications of the system to achieve detection and separation of… (more)

▼ Methods for the analysis of surfactants and proteins by Capillary Electrophoresis (CE) were investigated. Several modifications of the system to achieve detection and separation of these analytes were examined. These modifications included buffer additives, sample additives and surface treatment and modification of the fused silica capillary. For the analysis of anionic surfactants, the addition of an anionic IN absorbing compound to the buffer was investigated to achieve indirect detection of the non-absorbing surfactants. The effect on detection sensitivity and separation efficiency of the absorbing ion was examined. These parameters were affected by differences in the electrophoretic mobilities of the analytes in comparison to the absorbing ion. The use of organic modifiers was also investigated to minimize micelle formation of the surfactants which leads to zone spreading. For the analysis of serum and urine proteins, the use of high pH buffers was investigated to minimize solute/capillary surface interactions and achieve separation. At high pH's the proteins are negatively charged; therefore, they should be repelled by the negatively charged fused silica surface. To improve reproducibility of migration times of the proteins the addition of polyvinyl alcohol to the sample was also investigated. The polyvinyl alcohol improved reproducibility by reversibly covering the active sites on the capillary surface to minimize protein interactions. Migration time reproducibility was also improved by optimizing the capillary cleaning procedure. Lastly, the addition of methyl cellulose to the buffer to work as a dynamic molecular sieving medium was investigated to improve resolution. Analyte/ capillary surface interactions are a major limitation in CE especially for the analyses of proteins. The use of coated capillaries to eliminate these interactions has been widely investigated. However, reproducibility and degree of surface deactivation with these coating can be poor. In this work hydrothennal treatment of the fused silica capillary surface prior to deactivation was examined. Hydrothennal treatment was used to produce a homogenous surface prior to coating which leads to the production of more highly deactivated, reproducible columns. The effects of the treatment were studied by coating the surface with a silane and examining the influence of the coating on electroosmotic flow and analyte adsorption. Advisors/Committee Members: McNair, Harold M. (committeechair), Glanville, James O. (committee member), Long, Gary L. (committee member), Mason, John G. (committee member), Merola, Joseph S. (committee member).

Subjects/Keywords: Surface active agents; Proteins; Separation (Technology); LD5655.V856 1992.G638

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APA (6^th Edition):

Goebel, L. K. (1992). Electrokinetic separations involving surfactants and proteins. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/39443

Chicago Manual of Style (16^th Edition):

Goebel, Lisa Karen. “Electrokinetic separations involving surfactants and proteins.” 1992. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/39443.

MLA Handbook (7^th Edition):

Goebel, Lisa Karen. “Electrokinetic separations involving surfactants and proteins.” 1992. Web. 18 Jan 2021.

Vancouver:

Goebel LK. Electrokinetic separations involving surfactants and proteins. [Internet] [Doctoral dissertation]. Virginia Tech; 1992. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/39443.

Council of Science Editors:

Goebel LK. Electrokinetic separations involving surfactants and proteins. [Doctoral Dissertation]. Virginia Tech; 1992. Available from: http://hdl.handle.net/10919/39443

Virginia Tech

13. Reed, Gail L. Fast GC: Applications and Theoretical Studies.

Degree: PhD, Chemistry, 1999, Virginia Tech

URL: http://hdl.handle.net/10919/29085

► Experimental data are presented for the first time in support of a theoretical model of band broadening proposed by Blumberg (1997). This model addresses the… (more)

▼ Experimental data are presented for the first time in support of a theoretical model of band broadening proposed by Blumberg (1997). This model addresses the effects of the compressibility of the mobile phase in gas chromatography and presents an equation derived from only two mutually independent variables. Solutions of decane and tridecane in hexane were analyzed at pressures ranging from 15 to 150 psi. Six different columns were used that varied in length, internal diameter and film thickness. Theoretical plate heights were obtained from this data and plotted versus the average linear carrier gas velocity (Golay type plots). These plots showed that at high pressures the Blumberg model fit the experimental data statistically significantly better than the earlier model proposed by Golay. The Blumberg model also accurately predicts the relationship between the optimum linear carrier gas velocity and the temperature. The second part of this work explores the scope and limitations of fast temperature programming in the fast GC analyses of various sample types. These samples included polycyclic aromatic hydrocarbons (PAHs), hydrocarbons and food samples. Programming rates of up to 1200Â° C/min were used. These fast programming rates were obtained by using "flash"â ¢ temperature programming, controlled by resistive heating of a metal tube that enclosed a capillary column. The precision of peak data was found to be good, less than 5% for peak areas and 4% for retention times. However, a slight, but statistically significant decrease in peak areas was seen above programming rates of 240Â° C/min. Microwave assisted extraction (MAE) was used to extract 2,6-di-(tert-butyl)-4-methylphenol, BHT, from chewing gum and breakfast cereal. The extraction was followed by a fast GC analysis (less than 4 minutes) using "flash"â ¢ temperature programming. MAE reduced the sample preparation time, from hours to minutes, and consequently reduced, the total analysis time. Extraction times longer than 5 minutes gave decreased recoveries of BHT. Advisors/Committee Members: McNair, Harold M. (committeechair), Deck, Paul A. (committee member), Long, Gary L. (committee member), Glanville, James O. (committee member), Taylor, Larry T. (committee member).

Subjects/Keywords: Fast GC; microwave assisted extraction; Blumberg equation; BHT; food; Gas Chromatography; flash temperature programming; theoretical

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Reed, G. L. (1999). Fast GC: Applications and Theoretical Studies. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/29085

Chicago Manual of Style (16^th Edition):

Reed, Gail L. “Fast GC: Applications and Theoretical Studies.” 1999. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/29085.

MLA Handbook (7^th Edition):

Reed, Gail L. “Fast GC: Applications and Theoretical Studies.” 1999. Web. 18 Jan 2021.

Vancouver:

Reed GL. Fast GC: Applications and Theoretical Studies. [Internet] [Doctoral dissertation]. Virginia Tech; 1999. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/29085.

Council of Science Editors:

Reed GL. Fast GC: Applications and Theoretical Studies. [Doctoral Dissertation]. Virginia Tech; 1999. Available from: http://hdl.handle.net/10919/29085

Virginia Tech

14. Wang, Yuwen Jr. Sample Preparation/Concentration for Trace Analysis in GC/MS (A study of solid phase microextraction and headspace sampling).

Degree: PhD, Chemistry, 1997, Virginia Tech

URL: http://hdl.handle.net/10919/26404

► Solid Phase Microextraction (SPME) associated with Microwave Assisted Extraction (MAE)^(1-3) , on-line headspace derivatization ^(4-6) and the selectivity of different SPME coatings ⁽⁷⁾ were studied.… (more)

▼ Solid Phase Microextraction (SPME) associated with Microwave Assisted Extraction (MAE)^(1-3) , on-line headspace derivatization ^(4-6) and the selectivity of different SPME coatings ⁽⁷⁾ were studied. Trace amounts of Veltol ®, Veltol Plus® and short chain fatty acids in food samples were analyzed by GC/MS. Since SPME is not directly applicable to solid samples, SPME associated with MAE techniques was studied for solids, primarily food samples. The efficiency of classical solvent extraction and MAE was compared. The parameters which affect SPME, were optimized for the determination of Veltol® and Veltol Plus® in food products such as potato chips and coffee. The technique gave a detection limit of 2 ppb for Veltol Plus ® which is 200 times more sensitive than conventional GC technique. Headspace injection is characterized by simple and easy handling of complicated solid and solution matrices. Headspace injection, however, is not suitable for high molecular weight substances or non-volatile compounds. An on-line derivatization headspace technique was studied for short chain fatty acids. These samples are difficult to do by classical GC. The developed technique simplified the conventional derivatization procedures and combined the sample preparation and GC/MS analysis into one step. The thermostatting temperature, time, solvent and matrix effects were investigated. Low calorie fat and some agricultural samples were analyzed. The detection limit for acetic acid is 8 ppb. SPME is a novel sample introduction technique. The behavior of di(methylsiloxane), polyacrylate and Carbowax coatings on SPME fibers for compounds having different functional groups were investigated. The selectivities of the coating, sample pH and the sample temperature were investigated. Advisors/Committee Members: McNair, Harold M. (committeechair), Anderson, Mark R. (committee member), Long, Gary L. (committee member), Glanville, James O. (committee member), Dillard, John G. (committee member).

Subjects/Keywords: GC/MS; trace analysis; sample preparation/concentration; SPME; MAE

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APA (6^th Edition):

Wang, Y. J. (1997). Sample Preparation/Concentration for Trace Analysis in GC/MS (A study of solid phase microextraction and headspace sampling). (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/26404

Chicago Manual of Style (16^th Edition):

Wang, Yuwen Jr. “Sample Preparation/Concentration for Trace Analysis in GC/MS (A study of solid phase microextraction and headspace sampling).” 1997. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/26404.

MLA Handbook (7^th Edition):

Wang, Yuwen Jr. “Sample Preparation/Concentration for Trace Analysis in GC/MS (A study of solid phase microextraction and headspace sampling).” 1997. Web. 18 Jan 2021.

Vancouver:

Wang YJ. Sample Preparation/Concentration for Trace Analysis in GC/MS (A study of solid phase microextraction and headspace sampling). [Internet] [Doctoral dissertation]. Virginia Tech; 1997. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/26404.

Council of Science Editors:

Wang YJ. Sample Preparation/Concentration for Trace Analysis in GC/MS (A study of solid phase microextraction and headspace sampling). [Doctoral Dissertation]. Virginia Tech; 1997. Available from: http://hdl.handle.net/10919/26404

Virginia Tech

15. Ding, Hao. Influence of solution ionic strength on aggregation of novel water soluble phosphines and two phase catalysis.

Degree: PhD, Chemistry, 1995, Virginia Tech

URL: http://hdl.handle.net/10919/39609

Subjects/Keywords: chemical interaction; LD5655.V856 1995.D565

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APA (6^th Edition):

Ding, H. (1995). Influence of solution ionic strength on aggregation of novel water soluble phosphines and two phase catalysis. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/39609

Chicago Manual of Style (16^th Edition):

Ding, Hao. “Influence of solution ionic strength on aggregation of novel water soluble phosphines and two phase catalysis.” 1995. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/39609.

MLA Handbook (7^th Edition):

Ding, Hao. “Influence of solution ionic strength on aggregation of novel water soluble phosphines and two phase catalysis.” 1995. Web. 18 Jan 2021.

Vancouver:

Ding H. Influence of solution ionic strength on aggregation of novel water soluble phosphines and two phase catalysis. [Internet] [Doctoral dissertation]. Virginia Tech; 1995. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/39609.

Council of Science Editors:

Ding H. Influence of solution ionic strength on aggregation of novel water soluble phosphines and two phase catalysis. [Doctoral Dissertation]. Virginia Tech; 1995. Available from: http://hdl.handle.net/10919/39609

Virginia Tech

16. Xu, Jiannong. Equilibrium Melting Temperature Determination of Semicrystalline Polymers through Nonlinear Hoffman-Weeks Extrapolation and Secondary Crystallization of Ethylene/Styrene Copolymers.

Degree: PhD, Chemistry, 1999, Virginia Tech

URL: http://hdl.handle.net/10919/40263

► The applicability of the conventional Hoffman-Weeks (HW) linear extrapolation for the determination of the equilibrium melting temperatures of semicrystalline polymers is critically reviewed. It is… (more)

▼ The applicability of the conventional Hoffman-Weeks (HW) linear extrapolation for the determination of the equilibrium melting temperatures of semicrystalline polymers is critically reviewed. It is shown that the linear extrapolation of observed melting temperatures cannot, in general, provide a reliable estimate of the equilibrium melting temperature. A more rigorous nonlinear HW analysis is proposed in this dissertation, which yields more accurate estimates of the equilibrium melting temperatures for semicrystalline polymers. The proposed nonlinear HW analysis is successfully applied to the cases of isotactic polypropylene and poly(ethylene oxide). The predicted initial lamellar thickness as a function of the crystallization temperature matches well with experimental results and/or literature values. Results based on the nonlinear HW analysis are consistent with those obtained from the analysis of the temperature dependence of the crystal growth rates. The general applicability of the Lauritzen Hoffman (LH) secondary nucleation theory is also addressed for isotactic polypropylene and poly(ethylene oxide). While the LH theory provides an excellent account of the temperature dependence of spherulitic growth rates and ratio of nucleation constants for different regimes, it appears not to yield a meaningful value for the substrate length, L, for poly(ethylene oxide). In a second project, the effects of structural and topological constraints on the morphology, melting and crystallization behavior of ethylene/styrene copolymers are investigated. During cooling from the melt, the longest ethylene sequences crystallize into lamellae in the primary crystallization process, while the shorter ethylene sequences are suggested to form fringed micelles in the secondary crystallization process. Kinetic studies indicate that secondary crystallization is characterized by an Avrami exponent of Â½ which is consistent with a one dimensional, diffusion controlled growth. The increase in the melting temperature of secondary crystals with crystallization time is tentatively explained by a decrease in the molar conformational entropy of the remaining amorphous fraction as a result of secondary crystallization, although the possible role of an increase of crystal lateral dimensions with time cannot be rigorously ruled out. Advisors/Committee Members: Marand, Hervé L. (committeechair), Glanville, James O. (committee member), Shultz, Allan R. (committee member), Ward, Thomas C. (committee member), Wilkes, Garth L. (committee member).

Subjects/Keywords: Equilibrium Melting Temperature; Secondary Crystallization

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APA (6^th Edition):

Xu, J. (1999). Equilibrium Melting Temperature Determination of Semicrystalline Polymers through Nonlinear Hoffman-Weeks Extrapolation and Secondary Crystallization of Ethylene/Styrene Copolymers. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/40263

Chicago Manual of Style (16^th Edition):

Xu, Jiannong. “Equilibrium Melting Temperature Determination of Semicrystalline Polymers through Nonlinear Hoffman-Weeks Extrapolation and Secondary Crystallization of Ethylene/Styrene Copolymers.” 1999. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/40263.

MLA Handbook (7^th Edition):

Xu, Jiannong. “Equilibrium Melting Temperature Determination of Semicrystalline Polymers through Nonlinear Hoffman-Weeks Extrapolation and Secondary Crystallization of Ethylene/Styrene Copolymers.” 1999. Web. 18 Jan 2021.

Vancouver:

Xu J. Equilibrium Melting Temperature Determination of Semicrystalline Polymers through Nonlinear Hoffman-Weeks Extrapolation and Secondary Crystallization of Ethylene/Styrene Copolymers. [Internet] [Doctoral dissertation]. Virginia Tech; 1999. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/40263.

Council of Science Editors:

Xu J. Equilibrium Melting Temperature Determination of Semicrystalline Polymers through Nonlinear Hoffman-Weeks Extrapolation and Secondary Crystallization of Ethylene/Styrene Copolymers. [Doctoral Dissertation]. Virginia Tech; 1999. Available from: http://hdl.handle.net/10919/40263

Virginia Tech

17. Iler, H. Darrell. A study of the crystallization kinetics of isotactic polystyrene.

Degree: PhD, Chemistry, 1995, Virginia Tech

URL: http://hdl.handle.net/10919/39277

► The spherulitic growth rate data for a molecular weight series of isotactic polystyrene are analyzed in context of the Lauritzen-Hoffman kinetic theory of polymer crystallization.… (more)

▼ The spherulitic growth rate data for a molecular weight series of isotactic polystyrene are analyzed in context of the Lauritzen-Hoffman kinetic theory of polymer crystallization. The primary objectives of the study are to critically test the Lauritzen-Hoffinan theory under conditions not rigorously investigated before and to gain a better understanding of the molecular weight dependence of crystal growth rate for isotactic polystyrene. The analyses yield values for fundamental kinetic and thermodynamic quantities associated with polymer crystallization. The physical meaning of the resulting parameters is assessed by comparing these results to those obtained from methods independent of crystal growth rate or crystallization theory altogether. This study differs from others reported in the literature in a number of ways, such as, the narrow molecular weight distribution and the molecular weight range of polystyrenes investigated. Also, growth rate measurements were extended to higher temperatures and a more appropriate kinetic equation for crystal growth rate analysis was applied. The majority of published studies that have used the Lauritzen-Hoffman theory applied an approximated form of the kinetic equation which does not fully describe the temperature dependence of polymer crystallization. The results of the study show that a transition from molecular weight dependent to independent crystal growth rate occurs at a molecular weight of about 250,000 g/mole for isotactic polystyrene. Also, comparison of viscoelastic and crystal growth rate data indicate that the Vogel form of the transport term in the Lauritzen Hoffman kinetic growth rate equation correctly describes the temperature dependence of molecular transport for the crystallization process of isotactic polystyrene. Furthermore, the study suggests that the equilibrium melting temperature for the polymer is significantly higher than the value that has been generally accepted for the past 25 years. The study also provided the opportunity to investigate various other factors and theories associated with polymer crystallization. For example, the theoretical relationship between the crystal's lateral surface free energy, σ, and the characteristic ratio, C<sub>∞<sub>, was evaluated. Also, the spherulitic morphology as a function of molecular weight and temperature was examined by scanning electron microscopy, SEM. Advisors/Committee Members: Marand, Hervé L. (committeechair), Glanville, James O. (committee member), Tanko, James M. (committee member), Ward, Thomas C. (committee member), Wilkes, Garth L. (committee member).

Subjects/Keywords: morphology; isotactic poly(styrene); viscoelastic properties; Lauritzen-Hoffman theory; LD5655.V856 1995.I447

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APA (6^th Edition):

Iler, H. D. (1995). A study of the crystallization kinetics of isotactic polystyrene. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/39277

Chicago Manual of Style (16^th Edition):

Iler, H Darrell. “A study of the crystallization kinetics of isotactic polystyrene.” 1995. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/39277.

MLA Handbook (7^th Edition):

Iler, H Darrell. “A study of the crystallization kinetics of isotactic polystyrene.” 1995. Web. 18 Jan 2021.

Vancouver:

Iler HD. A study of the crystallization kinetics of isotactic polystyrene. [Internet] [Doctoral dissertation]. Virginia Tech; 1995. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/39277.

Council of Science Editors:

Iler HD. A study of the crystallization kinetics of isotactic polystyrene. [Doctoral Dissertation]. Virginia Tech; 1995. Available from: http://hdl.handle.net/10919/39277

Virginia Tech

18. Matthews, Kelly E. Elucidation of the aqueous equilibrium system of IrH2(PMe3)3Cl and periodic trends of the iridium (III) dihydrido tris(trimethylphosphino) series, IrH2(PMe3)3X.

Degree: PhD, Chemistry, 1994, Virginia Tech

URL: http://hdl.handle.net/10919/38258

Subjects/Keywords: Transition metal hydrides.; LD5655.V856 1994.M387

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APA (6^th Edition):

Matthews, K. E. (1994). Elucidation of the aqueous equilibrium system of IrH2(PMe3)3Cl and periodic trends of the iridium (III) dihydrido tris(trimethylphosphino) series, IrH2(PMe3)3X. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/38258

Chicago Manual of Style (16^th Edition):

Matthews, Kelly E. “Elucidation of the aqueous equilibrium system of IrH2(PMe3)3Cl and periodic trends of the iridium (III) dihydrido tris(trimethylphosphino) series, IrH2(PMe3)3X.” 1994. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/38258.

MLA Handbook (7^th Edition):

Matthews, Kelly E. “Elucidation of the aqueous equilibrium system of IrH2(PMe3)3Cl and periodic trends of the iridium (III) dihydrido tris(trimethylphosphino) series, IrH2(PMe3)3X.” 1994. Web. 18 Jan 2021.

Vancouver:

Matthews KE. Elucidation of the aqueous equilibrium system of IrH2(PMe3)3Cl and periodic trends of the iridium (III) dihydrido tris(trimethylphosphino) series, IrH2(PMe3)3X. [Internet] [Doctoral dissertation]. Virginia Tech; 1994. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/38258.

Council of Science Editors:

Matthews KE. Elucidation of the aqueous equilibrium system of IrH2(PMe3)3Cl and periodic trends of the iridium (III) dihydrido tris(trimethylphosphino) series, IrH2(PMe3)3X. [Doctoral Dissertation]. Virginia Tech; 1994. Available from: http://hdl.handle.net/10919/38258

Virginia Tech

19. Smith, Jennifer Houston. Chromatographic Properties of Silica-Based Monolithic HPLC Columns.

Degree: PhD, Chemistry, 2002, Virginia Tech

URL: http://hdl.handle.net/10919/29953

► Silica-based monolithic HPLC columns contain a novel chromatographic support in which the traditional particulate packing has been replaced with a single, continuous network (monolith) of… (more)

▼ Silica-based monolithic HPLC columns contain a novel chromatographic support in which the traditional particulate packing has been replaced with a single, continuous network (monolith) of porous silica. The main advantage of such a network is decreased backpressure due to macropores (2 μM) throughout the network. This allows high flow rates, and hence fast analyses that are unattainable with traditional particulate columns. The Chromolith SpeedROD™ (EM Science, Gibbstown NJ) is a commercially available silica-based monolithic column. This work investigated the chromatographic properties of the 50x4.60 mm (ODS) SpeedROD™. Data fit to the van Deemter equation (mean square error=0.834) indicated that the van Deemter model was valid for monolithic columns. An effective particle size of 4 μM for the SpeedROD™ column was assigned by comparing the minimum of van Deemter curves with a series of particulate columns having various particle diameters. Separation Impedance (E), an empirically derived measure of column performance, was calculated as an alternate method of evaluating column efficiency. Data collected using this model confirmed monolithic columns behaves as a (more efficient) 3 μM column. A series of experiments were designed to compare the effects of mobile phase strength and mobile phase viscosity between the SpeedROD™ column and a particulate column. The results indicated both solvent strength and viscosity have effects on the monolithic column at the optimum linear velocity. A fast (90 s) HPLC method was developed using the SpeedROD™ column and a seven-component test mixture with a large range of hydrophobicities. The precision for both retention time and peak area was measured at high linear velocities (8 mL/min) and the percent relative standard deviation (RSD) calculated. Column to column reproducibility (n=6) was measured. The overall percent RSD ranged from 0.25% to 4.56% for retention time and from 1.08% to 6.77% for peak area. Run to run reproducibility (n=15) was measured for all six columns. Averages ranged for retention time from 0.89% to 5.09% RSD and for peak area from 4.65% to 6.18% RSD. Applications for the SpeedROD™ column with various sample types were developed and discussed. These methods demonstrated the effectiveness of the SpeedROD™ at fast flow rates. Advisors/Committee Members: McNair, Harold M. (committeechair), Viers, Jimmy W. (committee member), Anderson, Mark R. (committee member), Glanville, James O. (committee member), Taylor, Larry T. (committee member).

Subjects/Keywords: chromatography; monolith; HPLC

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Smith, J. H. (2002). Chromatographic Properties of Silica-Based Monolithic HPLC Columns. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/29953

Chicago Manual of Style (16^th Edition):

Smith, Jennifer Houston. “Chromatographic Properties of Silica-Based Monolithic HPLC Columns.” 2002. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/29953.

MLA Handbook (7^th Edition):

Smith, Jennifer Houston. “Chromatographic Properties of Silica-Based Monolithic HPLC Columns.” 2002. Web. 18 Jan 2021.

Vancouver:

Smith JH. Chromatographic Properties of Silica-Based Monolithic HPLC Columns. [Internet] [Doctoral dissertation]. Virginia Tech; 2002. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/29953.

Council of Science Editors:

Smith JH. Chromatographic Properties of Silica-Based Monolithic HPLC Columns. [Doctoral Dissertation]. Virginia Tech; 2002. Available from: http://hdl.handle.net/10919/29953

Virginia Tech

20. Hamner, Vincent N. Hydroxypropylmethylcellulose: A New Matrix for Solid-Surface Room-Temperature Phosphorimetry.

Degree: PhD, Chemistry, 1999, Virginia Tech

URL: http://hdl.handle.net/10919/37809

► This thesis reports an investigation of hydroxypropylmethylcellulose (HPMC) as a new solid-surface room-temperature phosphorescence (SSRTP) sample matrix. The high background phosphorescence originating from filter paper… (more)

▼ This thesis reports an investigation of hydroxypropylmethylcellulose (HPMC) as a new solid-surface room-temperature phosphorescence (SSRTP) sample matrix. The high background phosphorescence originating from filter paper substrates can interfere with the detection and quantitation of trace-level analytes. High-purity grades of HPMC were investigated as SSRTP substrates in an attempt to overcome this limitation. When compared directly to filter paper, HPMC allows the spectroscopist to achieve greater sensitivity, lower limits of detection (LOD), and lower limits of quantitation (LOQ) for certain phosphor/heavy-atom combinations since SSRTP signal intensities are stronger. For example, the determination of the analytical figures of merit for a naphthalene/sodium iodide/HPMC system resulted in a calibration sensitivity of 2.79, LOD of 4 ppm (3 ng), and LOQ of 14 ppm (11 ng). Corresponding investigations of a naphthalene/sodium iodide/filter paper system produced a calibration sensitivity of 0.326, LOD of 33 ppm (26 ng), and LOQ of 109 ppm (86 ng). Extended purging with dry-nitrogen gas yields improved sensitivities, lower LOD's, and lower LOQ's in HPMC matrices when LOD and LOQ are calculated according to the IUPAC guidelines.To test the universality of HPMC, qualitative SSRTP spectra were obtained for a wide variety of probe phosphors offering different molecular sizes, shapes, and chemical functionalities. Suitable spectra were obtained for the following model polycyclic aromatic hydrocarbons (PAHs): naphthalene, p-aminobenzoic acid, acenaphthene, phenanthrene, 2-naphthoic acid, 2-naphthol, salicylic acid, and triphenylene.Filter paper and HPMC substrates are inherently anisotropic, non-heterogeneous media. Since this deficiency cannot be addressed experimentally, a robust statistical method is examined for the detection of questionable SSRTP data points and the deletion of outlying observations. If discordant observations are discarded, relative standard deviations are typically reduced to less than 10% for most SSRTP data sets. Robust techniques for outlier identification are superior to traditional methods since they operate at a high level of efficiency and are immune to masking effects.The process of selecting a suitable sample support material often involves considerable trial-and-error on the part of the analyst. A mathematical model based on Hansen's cohesion parameter theory is developed to predict favorable phosphor-substrate attraction and interactions. The results of investigations using naphthalene as a probe phosphor and sodium iodide as an external heavy-atom enhancer support the cohesion parameter model.This document includes a thorough description of the fundamental principles of phosphorimetry and provides a detailed analysis of the theoretical and practical concerns associated with performing SSRTP. In order to better understand the properties of both filter paper and HPMC, a chapter is devoted to the discussion of the cellulose biopolymer. Experimental results and interpretations are… Advisors/Committee Members: Dessy, Raymond E. (committeechair), Anderson, Mark R. (committee member), Tissue, Brian M. (committee member), Merola, Joseph S. (committee member), Glanville, James O. (committee member).

Subjects/Keywords: Outliers; Cellulose; Cohesion (or Solubility) Parameters; Robust Statistics; Phosphorescence Spectroscopy; Hydroxypropylmethylcellulose (HPMC)

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APA (6^th Edition):

Hamner, V. N. (1999). Hydroxypropylmethylcellulose: A New Matrix for Solid-Surface Room-Temperature Phosphorimetry. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/37809

Chicago Manual of Style (16^th Edition):

Hamner, Vincent N. “Hydroxypropylmethylcellulose: A New Matrix for Solid-Surface Room-Temperature Phosphorimetry.” 1999. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/37809.

MLA Handbook (7^th Edition):

Hamner, Vincent N. “Hydroxypropylmethylcellulose: A New Matrix for Solid-Surface Room-Temperature Phosphorimetry.” 1999. Web. 18 Jan 2021.

Vancouver:

Hamner VN. Hydroxypropylmethylcellulose: A New Matrix for Solid-Surface Room-Temperature Phosphorimetry. [Internet] [Doctoral dissertation]. Virginia Tech; 1999. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/37809.

Council of Science Editors:

Hamner VN. Hydroxypropylmethylcellulose: A New Matrix for Solid-Surface Room-Temperature Phosphorimetry. [Doctoral Dissertation]. Virginia Tech; 1999. Available from: http://hdl.handle.net/10919/37809

Virginia Tech

21. Tiwari, Rajesh Kumar. The Thermal Stability of Anodic Oxide Coatings - Strength and Durability of Adhesively Bonded Ti-6Al-4V Alloy.

Degree: PhD, Chemistry, 2002, Virginia Tech

URL: http://hdl.handle.net/10919/28528

► The lap shear strength of chromic acid anodized, primed, Ti-6Al-4V alloy bonded with a high performance FM-5 polyimide adhesive has been investigated as a function… (more)

▼ The lap shear strength of chromic acid anodized, primed, Ti-6Al-4V alloy bonded with a high performance FM-5 polyimide adhesive has been investigated as a function of thermal treatment for selected times at various temperatures in air. The research findings indicate that the lap shear strength decreases with the increase in duration of the thermal treatment at constant temperature and with the increase in temperature at constant time. The bond fails increasingly in the oxide coating with increasing treatment temperature and time of treatment. Surface analysis results for debonded specimens suggest that the process leading to failure is the formation of fluorine-containing materials within the oxide, which weakens the adherend-adhesive bond. The formation of the fluorine components is facilitated by treatment at elevated temperatures. This study suggests that the presence of fluoride ions in the anodic oxide coating, prior to bonding, is detrimental to the bond strength of adhesively bonded Ti-alloy when exposed to high temperatures. The wedge test configuration was used to investigate the influence of temperature on the bond durability of adhesively bonded chromic acid anodized Ti-6Al-4V alloy in air. Based on the average crack length vs. exposure time data, the bond durability varied in the order -25Â°C > 24Â°C > 177Â°C. In each case, the bonded joint failed cohesively within the adhesive, irrespective of the temperature of exposure. XPS analysis and scanning electron photomicrographs of failure surfaces revealed that the failure occurred at the scrim cloth/adhesive interface. The influence of thermal treatment history on the bond durability of adhesively bonded chromic acid anodized Ti-6Al-4V alloy immersed in boiling water was also investigated. The average crack length vs. immersion time indicated no significant differences for specimens that were thermally treated and then bonded compared to the non-thermally treated specimens. In addition, the failure mode was cohesive within the adhesive for specimens prepared using various thermal treatment conditions. The crack growths for samples treated for 0.5 hour and 1.0 hour and for non-thermally treated specimens for any given exposure time were equivalent. In addition, cohesive failure (failure within adhesive) was observed for each specimen under each treatment condition. The specimens that were bonded and then thermally treated for 3 hours, failed in the oxide coating immediately upon insertion of the wedge. Surface analysis results for debonded specimens suggest that the process leading to failure is the formation of fluorine-containing materials within the oxide. The measured average activation energy for the formation of aluminum fluoride species is 149 kJ/mol. The high activation energy suggests that the rate of aluminum fluoride formation is substantial only at high temperatures. In summary, the presence of fluorides in the anodic oxide coatings prior to bonding is detrimental to the overall strength and durability of adhesively bonded… Advisors/Committee Members: Dillard, John G. (committeechair), Dorn, Harry C. (committee member), Ward, Thomas C. (committee member), Glanville, James O. (committee member), Anderson, Mark R. (committee member).

Subjects/Keywords: chromic acid anodization; polyimide; FM-5 adhesive; titanium 6Al-4V; thermal treatment; lap shear test; aluminum fluoride; oxide stability; durability; wedge test

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APA (6^th Edition):

Tiwari, R. K. (2002). The Thermal Stability of Anodic Oxide Coatings - Strength and Durability of Adhesively Bonded Ti-6Al-4V Alloy. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/28528

Chicago Manual of Style (16^th Edition):

Tiwari, Rajesh Kumar. “The Thermal Stability of Anodic Oxide Coatings - Strength and Durability of Adhesively Bonded Ti-6Al-4V Alloy.” 2002. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/28528.

MLA Handbook (7^th Edition):

Tiwari, Rajesh Kumar. “The Thermal Stability of Anodic Oxide Coatings - Strength and Durability of Adhesively Bonded Ti-6Al-4V Alloy.” 2002. Web. 18 Jan 2021.

Vancouver:

Tiwari RK. The Thermal Stability of Anodic Oxide Coatings - Strength and Durability of Adhesively Bonded Ti-6Al-4V Alloy. [Internet] [Doctoral dissertation]. Virginia Tech; 2002. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/28528.

Council of Science Editors:

Tiwari RK. The Thermal Stability of Anodic Oxide Coatings - Strength and Durability of Adhesively Bonded Ti-6Al-4V Alloy. [Doctoral Dissertation]. Virginia Tech; 2002. Available from: http://hdl.handle.net/10919/28528

Virginia Tech

22. Combs, Michael T. Optimal Analysis of Sulfonamides From Biological Matrices Using Supercritical Fluids.

Degree: PhD, Chemistry, 1997, Virginia Tech

URL: http://hdl.handle.net/10919/30564

► The objective of this research was to develop new sample preparation procedures for the isolation of sulfonamides, as well as, to determine the applicability of… (more)

▼ The objective of this research was to develop new sample preparation procedures for the isolation of sulfonamides, as well as, to determine the applicability of employing on-line nitrogen selective and mass spectrometric detection methods. The first phase of this research investigated the effect of temperature and pressure on the supercritical fluid extraction (SFE) of sulfonamides from a spiked sand matrix. Temperature effects were either positive or negative with respect to extraction rate and total recovery, depending on the pressure and extraction fluid employed. The second portion of this research compared trifluoromethane (CHF3) and carbon dioxide (CO2) as fluids for the extraction of sulfonamides from spiked non-fat dry milk, beef liver, and egg yolk were found to be more selective using CHF3 than CO2. The polar trifluoromethane improved the extraction efficiency of the polar sulfonamides from the biological matrices and also reduced the amount of co-extractives. The next phase of this research considered the effect of organic modifier and CO2 in the SFE of sulfonamides from chicken liver, beef liver and egg yolk. Methanol, ethanol, acetone, acetonitrile were compared to determine optimum conditions. A SFE method employing 20% acetonitrile modified CO2 yielded quantitative recovery of sulfonamides from chicken liver, but 20% acetone modified CO2 was required to obtain quantitative recovery from beef liver. Either 20% acetone or 20% acetonitrile yielded quantitative recovery from egg yolk. The last phase of this research focused on the evaluation of selective detection methods for sulfonamide analysis. Chemiluminescence nitrogen detection (CLND) parameters were optimized for use with packed column supercritical fluid chromatography (SFC) yielding a minimum detectable quantity (MDQ) of 5 ng of sulfamethazine, on column. Improvements in the detector design decreased the MDQ to 0.5 ng, while, decreasing the column diameter further reduced the MDQ to 125 pg. The second part of this phase evaluated PLC/Atmospheric pressure chemical ionization (APCI) mass spectrometry for the detection of sulfonamides. Sensitivity in selective ion mode was found to be as low as 50 pg on column for sulfamethazine. Supercritical fluid extracts of sulfonamides spiked at 100Î¼g/kg in chicken liver were found to be readily detected by this method. Advisors/Committee Members: Taylor, Larry L. (committeechair), Castagnoli, Neal Jr. (committee member), McNair, Harold M. (committee member), Glanville, James O. (committee member), Anderson, Mark R. (committee member).

Subjects/Keywords: SFE; mass spectrometry; egg yolk; chromatography; sulfonamides; beef liver; chicken liver; supercritical; extraction; atmospheric pressure chemical ionization; CLND; HPLC/MS; SFC

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Combs, M. T. (1997). Optimal Analysis of Sulfonamides From Biological Matrices Using Supercritical Fluids. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/30564

Chicago Manual of Style (16^th Edition):

Combs, Michael T. “Optimal Analysis of Sulfonamides From Biological Matrices Using Supercritical Fluids.” 1997. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/30564.

MLA Handbook (7^th Edition):

Combs, Michael T. “Optimal Analysis of Sulfonamides From Biological Matrices Using Supercritical Fluids.” 1997. Web. 18 Jan 2021.

Vancouver:

Combs MT. Optimal Analysis of Sulfonamides From Biological Matrices Using Supercritical Fluids. [Internet] [Doctoral dissertation]. Virginia Tech; 1997. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/30564.

Council of Science Editors:

Combs MT. Optimal Analysis of Sulfonamides From Biological Matrices Using Supercritical Fluids. [Doctoral Dissertation]. Virginia Tech; 1997. Available from: http://hdl.handle.net/10919/30564

Virginia Tech

23. Jordan, Sheri Lynne. Hyphenated fourier transform infrared spectrometry: techniques for separations and analysis.

Degree: PhD, Chemistry, 1995, Virginia Tech

URL: http://hdl.handle.net/10919/39286

► The following work describes the instrumentation and application of hyphenated FT-IR techniques specifically involving supercritical fluid extraction (SFE), supercritical fluid chromatography (SFC), and liquid chromatography… (more)

▼ The following work describes the instrumentation and application of hyphenated FT-IR techniques specifically involving supercritical fluid extraction (SFE), supercritical fluid chromatography (SFC), and liquid chromatography (LC). Three studies are presented. The first involves the application of SFE/FT-IR towards the extraction of finishes from textile fibers. SFE has previously been applied to less complex finish systems. The proposed method making use of intermediate trapping is viable for more complex systems that show limited solubility in a supercritical fluid. Quantification of the percent finish on yarn was performed and results were favorable when compared with plant data. The range of applications was expanded to on-line SFE/SFC in the extraction and analysis of components from the polymer matrix itself. SFE/SFC/FT-IR was used to identify extractable components from a variety of Nylons. Following identification of one of the primary extractables, caprolactam, SFE/SFC was used to quantitate the amount of residual starting material in a Nylon copolymer. The second study involves the extractables in polystyrene which is a softer polymer with respect to solubility of components in supercritical CO ₂. Dimers and trimers as well as processing agents were identified via FT-IR with relatively mild supercritical extraction conditions. Following these two studies was the expansion of hyphenated FT -IR to mobile phase elimination. A system optimization was carried out using polymer additive standards. The effects of nebulizer flow, sheath flow, and sheath temperature were shown. The data were analyzed at in terms of library matches as well as GramSchmidt reconstruction peak heights. Peak intensities were the primary source for choosing optimum conditions. Under optimized conditions, approximately 200 ng of analyte were analyzed and found to be above the limit of detection. The applicability of the interface was demonstrated by the identification/analysis of triclosan, an antibacterial agent, in Colgate toothpaste. Aside from the identification of the analyte this study was used to show the effect of deposition parameters such as disk rotation rate as well as the effectiveness of FT-IR spectral library searches. The analysis of triglycerides was also carried out to show the effectiveness of using LC/FTIR for viscous liquids which are difficult analytes to deposit onto a solid substrate. Using this FT-IR technique allowed one to look at the degree of saturation/unsaturation in an olive oil sample. The linearity of the method was shown using a set of triglyceride standards. Lastly, the feasibility of using the commercially manufactured mobile phase elimination interface for SFC was demonstrated. Additive standard was deposited using both pure and methanol modified CO₂. No effluent split mechanism was used for decompressed flows up to 150 mL/min. Detection limits are proposed to fall in the low (10 - 25) ng range. The infrared spectra are enhanced over those acquired with a flow cell interface… Advisors/Committee Members: Taylor, Larry T. (committeechair), Glanville, James O. (committee member), Long, Gary L. (committee member), Brewer, Karen J. (committee member), McNair, Harold M. (committee member).

Subjects/Keywords: Supercritical Fluids; FT-IR; Hyphenated Techniques; SFE; SFC; LD5655.V856 1995.J673

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APA (6^th Edition):

Jordan, S. L. (1995). Hyphenated fourier transform infrared spectrometry: techniques for separations and analysis. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/39286

Chicago Manual of Style (16^th Edition):

Jordan, Sheri Lynne. “Hyphenated fourier transform infrared spectrometry: techniques for separations and analysis.” 1995. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/39286.

MLA Handbook (7^th Edition):

Jordan, Sheri Lynne. “Hyphenated fourier transform infrared spectrometry: techniques for separations and analysis.” 1995. Web. 18 Jan 2021.

Vancouver:

Jordan SL. Hyphenated fourier transform infrared spectrometry: techniques for separations and analysis. [Internet] [Doctoral dissertation]. Virginia Tech; 1995. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/39286.

Council of Science Editors:

Jordan SL. Hyphenated fourier transform infrared spectrometry: techniques for separations and analysis. [Doctoral Dissertation]. Virginia Tech; 1995. Available from: http://hdl.handle.net/10919/39286

Virginia Tech

24. Shi, Heng. Supercritical Fluid Chromatography with Chemiluminescent Nitrogen and Sulfur Detection.

Degree: PhD, Chemistry, 1997, Virginia Tech

URL: http://hdl.handle.net/10919/30546

► The need for sensitive and selective detectors in supercritical fluid chromatography (SFC) is particularly evident since SFC can be used to analyze classes of compounds… (more)

▼ The need for sensitive and selective detectors in supercritical fluid chromatography (SFC) is particularly evident since SFC can be used to analyze classes of compounds that are not readily amenable to either gas chromatography (GC) or liquid chromatography (LC). These compounds include species that are nonvolatile or thermally labile and , in addition, contain no chromophore that can be used for spectrophoto detection. The objective of this research is therefore to interface selective chemilumninescent detectors with SFC in the sensitive detection of nitrogen- and/or sulfur containing compounds. The chemiluminecent nitrogen detector (CLND), a gas-phase detector which is specific for nitrogen-containing compounds, was first evaluated as a detector for use with capillary SFC. The potential use of the CLND for food flavor and petroleum samples was demonstrated. In addition to equimolar nitrogen response, the CLND showed good sensitivity and large linear dynamic range. Minimum detectable quantity (MDQ) was 60 pg of nitrogen with a linear range of over 3 orders of magnitude. Nitrogen to carbon selectivity of 105 was obtained. Capillary SFC with simultaneous flame ionization and chemiluminescent detection was also demonstrated. The second portion of the research investigated the CLND for packed column SFC with methanol modified CO2. The only modification made in the CLND for packed column SFC is the pyrolysis furnace. The CLND and UV were used to interface with SFC via a post-column split. Methanol-modified CO2 was also demonstrated to be compatible with the CLND even with a high mobile phase flow rate. The use of pressure and modifier programs appears to be feasible as is evidenced by the baseline studies which have been performed, as well as by the applications demonstrated. The last portion of the research focused on the evaluation of a new generation sulfur chemiluminescent detector (SCLD), which is also a gas-phase detector, with packed column SFC using both pure and methanol modified CO2. The minimum detectable quantities were determined to be 2.6 pg or 14 pg sulfur for mobile phase employing pure CO2 or 8% methanol modified CO2 respectively. The evaluation study also showed excellent selectivity and linearity, as well as day-to-day repeatability. The capabilities of the SFC-SCLD system for sulfur speciation and detection of thermally labile pesticides and polar sulfonamides, as well as petrochemical samples were presented. Advisors/Committee Members: Taylor, Larry T. (committeechair), Viers, Jimmy W. (committee member), Glanville, James O. (committee member), McNair, Harold M. (committee member), Bell, Harold M. (committee member).

Subjects/Keywords: supercritical fluid chromatography; chemiluminescence detection; CLND; SCLD; pharmaceuticals; pesticides; food flavor

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Shi, H. (1997). Supercritical Fluid Chromatography with Chemiluminescent Nitrogen and Sulfur Detection. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/30546

Chicago Manual of Style (16^th Edition):

Shi, Heng. “Supercritical Fluid Chromatography with Chemiluminescent Nitrogen and Sulfur Detection.” 1997. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/30546.

MLA Handbook (7^th Edition):

Shi, Heng. “Supercritical Fluid Chromatography with Chemiluminescent Nitrogen and Sulfur Detection.” 1997. Web. 18 Jan 2021.

Vancouver:

Shi H. Supercritical Fluid Chromatography with Chemiluminescent Nitrogen and Sulfur Detection. [Internet] [Doctoral dissertation]. Virginia Tech; 1997. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/30546.

Council of Science Editors:

Shi H. Supercritical Fluid Chromatography with Chemiluminescent Nitrogen and Sulfur Detection. [Doctoral Dissertation]. Virginia Tech; 1997. Available from: http://hdl.handle.net/10919/30546

Virginia Tech

25. Armstrong, Stephanye Dawn. Microwave-Assisted Extraction for the Isolation of Trace Systemic Fungicides from Woody Plant Material.

Degree: PhD, Chemistry, 1999, Virginia Tech

URL: http://hdl.handle.net/10919/27997

► The extraction and recovery of trace organic material from semi-solid and solid matrices is often the slowest and most error-prone step of an analytical method.… (more)

▼ The extraction and recovery of trace organic material from semi-solid and solid matrices is often the slowest and most error-prone step of an analytical method. The conventional liquid extraction techniques for solids and semi-solids materials (Soxhlet) have two main disadvantages. The first, large volumes of organic solvent are required, which can lead to sample contamination and "losses" due to volatilization during concentration steps. The second, to achieve an exhaustive extraction can require several hours to days. With the development of sophisticated instrumentation with detection limits in the picogram and femtogram levels, pressure is finally felt within the analytical community to develop and validate sample preparation procedures which can be used to rapidly isolate trace level organics from complex matrices.Because of its applicability to solid, semi-solid, and liquid matrices microwave-assisted (MAE) extraction has emerged as a powerful sample preparation technique. The objective of this research was to evaluate directly focused microwave energy for the isolation of systemic fungicide residues from woody plant tissues.The hallmark of microwave extraction (MAE) is accelerated dissolution kinetics as a consequence of the rapid heating processes that occur when a microwave field is applied to a sample. The current popularity of MAE resides mainly on its applicability to a wide range of sample types because the selectivity can be easily manipulated by altering solvent polarities.Propiconazole is a systemic fungicide, used to combat the fungal pathogen Ophiostoma ulmi, the casual agent of Dutch elm disease (DED). It was successfully extracted from treated Ulmus americana (elm tree) using MAE with a percent recovery of 395% in 15 minutes. Until now, techniques for rapid and efficient extraction of polar material from wood were non-existent. This work produces results much quicker than Supercritical Fluid Extraction (SFE). The influence of pH, microwave power, and time on extraction efficiency was also investigated. The extraction methodology was optimized and statistically validated.This MAE method combined with GC-MS was used to study the diffusion patterns and degradation of propiconazole in tree bark over extended time periods. Because of the complex nature of woody plant systems, it was realized that a more theoretical means must be used to determine the degradation rate of propiconazole in water systems. As a result, propiconazole was reacted with water under controlled temperature and pH conditions; to measure the degradation rate of propiconazole.The internal pH of elm sap is about 6.0; the slightly acidic environment and natural enzymes within the xylem vessels are known to catalyze the degradation of propiconazole (1). Novartis Inc. has marketed propiconazole as having fungicidal effects in injected elms for nearly two years. Our degradation studies have indicated much shorter lifetimes. To confirm our fate studies, the activation energy for the degradation reaction of propiconazole was… Advisors/Committee Members: Tissue, Brian M. (committee member), Glanville, James O. (committee member), Bell, Harold M. (committee member), Stipes, R. Jay (committee member), McNair, Harold M. (committee member).

Subjects/Keywords: Fungicides and Wood Tissue; GC-MS; Sample Preparation; MAE

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Armstrong, S. D. (1999). Microwave-Assisted Extraction for the Isolation of Trace Systemic Fungicides from Woody Plant Material. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/27997

Chicago Manual of Style (16^th Edition):

Armstrong, Stephanye Dawn. “Microwave-Assisted Extraction for the Isolation of Trace Systemic Fungicides from Woody Plant Material.” 1999. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/27997.

MLA Handbook (7^th Edition):

Armstrong, Stephanye Dawn. “Microwave-Assisted Extraction for the Isolation of Trace Systemic Fungicides from Woody Plant Material.” 1999. Web. 18 Jan 2021.

Vancouver:

Armstrong SD. Microwave-Assisted Extraction for the Isolation of Trace Systemic Fungicides from Woody Plant Material. [Internet] [Doctoral dissertation]. Virginia Tech; 1999. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/27997.

Council of Science Editors:

Armstrong SD. Microwave-Assisted Extraction for the Isolation of Trace Systemic Fungicides from Woody Plant Material. [Doctoral Dissertation]. Virginia Tech; 1999. Available from: http://hdl.handle.net/10919/27997

Virginia Tech

26. Eckard, Phyllis R. The Investigation of Primary and Secondary Modifiers in the Extraction and Separation of Neutral and Ionic Pharmaceutical Compounds with Pure and Modified Carbon Dioxide.

Degree: PhD, Chemistry, 1998, Virginia Tech

URL: http://hdl.handle.net/10919/30500

► A successful supercritical fluid extraction method includes removal of the analyte from the matrix into the bulk fluid as well as trapping or concentration of… (more)

▼ A successful supercritical fluid extraction method includes removal of the analyte from the matrix into the bulk fluid as well as trapping or concentration of the analyte prior to analysis. In the first phase of this research, the trapping capacities of three solid-phase traps (glass beads, 50/50 (w/w) glass beads/octadecylsilica), 50/50 (w/w) Porapak Q®/glass beads) were determined as a function of trap composition for a mixture of components varying in polarity and volatility. The Porapak Q®/glass beads mixture was found to be the most successful solidphase investigated exhibiting the highest trapping capacity. The use of the Porapak Q®/glass beads as a solid-phase trap was investigated in later extraction studies in this dissertation. The extraction of highly polar, multifunctional analytes may not be completely successful with modified carbon dioxide, therefore, a secondary modifier (i.e. additive) may be added directly to the extraction fluid in hopes of improving the recoveries. In the second phase of this research, the effect of secondary modifiers in the subcritical fluid extraction of lovastatin from in-house prepared tablet powder mixtures and MEVACOR® tablets was investigated. The effect of in-line methanol-modifier percentage, additive type (acidic, basic, neutral) to the in-line methanol, and additive concentration on the extraction efficiency were examined. The extraction recoveries of lovastatin from MEVACOR® tablets were shown to be highly dependent on methanol concentration and additive type. Isopropylamine was shown to be the most successful additive investigated. An optimized and reproducible extraction method was developed. The extraction of ionic compounds with carbon dioxide may be difficult due to the high polarity of the compounds. In the third phase of this research, the addition of ion-pairing additives to the matrix in hopes of forming an ion-pair complex of reduced analyte polarity was investigated. Therefore, a screening study consisting of a fractional-factorial design was performed in order to identify the factors which contribute most to the recovery of an anionic species, triphenylphosphinetrisulfonate (TPPTS), from a spiked-sand surface employing supercritical fluid extraction with carbon dioxide. The experimental parameters investigated were: type of ion-pairing additive (i.e. tetralkylammonium hydrogen sulfates) and its concentration, carbon dioxide density, extraction temperature, static extraction time, CO₂ mass used, liquid CO₂ flow rate, and the volume of methanol spiked into the matrix prior to extraction. Of the eight factors investigated, four factors were identified as significantly affecting the recovery of the anionic species. They were: 1) ion-pairing reagent added to the spiked sand surface and its concentration; 2) static extraction time; and 3) volume of methanol present in the extraction vessel. The experimental parameters and settings identified as influential by the statistical approach were later shown in concert to yield 100% recovery of TPPTS from the… Advisors/Committee Members: Taylor, Larry T. (committeechair), Slack, Gregory C. (committee member), McNair, Harold M. (committee member), Long, Gary L. (committee member), Glanville, James O. (committee member), Castagnoli, Neal Jr. (committee member).

Subjects/Keywords: Secondary Modifiers; Trapping Capacity; Pharmaceuticals; Extraction; Chromatography; Supercritical; Triphenylphosphinetrisulfonate; Pseudoephedrine Hydrochloride; Additives; Ion-Pairing; SFC; SFE; MEVACORÂ®; Phospholipids

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6^th Edition):

Eckard, P. R. (1998). The Investigation of Primary and Secondary Modifiers in the Extraction and Separation of Neutral and Ionic Pharmaceutical Compounds with Pure and Modified Carbon Dioxide. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/30500

Chicago Manual of Style (16^th Edition):

Eckard, Phyllis R. “The Investigation of Primary and Secondary Modifiers in the Extraction and Separation of Neutral and Ionic Pharmaceutical Compounds with Pure and Modified Carbon Dioxide.” 1998. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/30500.

MLA Handbook (7^th Edition):

Eckard, Phyllis R. “The Investigation of Primary and Secondary Modifiers in the Extraction and Separation of Neutral and Ionic Pharmaceutical Compounds with Pure and Modified Carbon Dioxide.” 1998. Web. 18 Jan 2021.

Vancouver:

Eckard PR. The Investigation of Primary and Secondary Modifiers in the Extraction and Separation of Neutral and Ionic Pharmaceutical Compounds with Pure and Modified Carbon Dioxide. [Internet] [Doctoral dissertation]. Virginia Tech; 1998. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/30500.

Council of Science Editors:

Eckard PR. The Investigation of Primary and Secondary Modifiers in the Extraction and Separation of Neutral and Ionic Pharmaceutical Compounds with Pure and Modified Carbon Dioxide. [Doctoral Dissertation]. Virginia Tech; 1998. Available from: http://hdl.handle.net/10919/30500

Virginia Tech

27. Cabusas, Maria Elena Ybarbia III. Chiral Separations on HPLC Derivatized Polysaccharide CSPs: Temperature, Mobile Phase and Chiral Recognition Mechanism Studies.

Degree: PhD, Chemistry, 1998, Virginia Tech

URL: http://hdl.handle.net/10919/30426

► Direct chiral separations of the non-steroidal drugs of 2-methylarylpropionic acids (profens) on the chiral stationary phases (CSPs) of amylose tris(3,5-dimethylphenyl-carbamate), Chiralpak AD, and cellulose tris(3,5-dimethylphenylcarbamate),… (more)

▼ Direct chiral separations of the non-steroidal drugs of 2-methylarylpropionic acids (profens) on the chiral stationary phases (CSPs) of amylose tris(3,5-dimethylphenyl-carbamate), Chiralpak AD, and cellulose tris(3,5-dimethylphenylcarbamate), Chiralcel OD, were investigated. Chiralpak AD and Chiralcel OD are CSPs coated on silica gel and have the same type of constituents. However, they have different higher order structures arising from their different arrangements of the glucose units, i.e., the former has an a-(1,4)-D-glucose linkage and the latter has a b-(1,4)-D-glucose linkage. The orders of optimum enantioselectivity of racemic acids were reversed on the two CSPs which demonstrated that the enantioseparating abilities of these CSPs are complementary. This phenomenon also confirmed that the chiral recognition abilities of both CSPs were dependent on their higher order structures. Mechanisms for retention and chiral recognition for the separation of racemic 2-methylarylpropionic acids on Chiralpak AD and Chiralcel OD were explored. In depth studies of the dependence of retention and enantioselectivity on temperature and mobile phase compositions were made. The thermodynamic parameters, the differences in free energy, enthalpy, and entropy of association between enantiomers and the CSP were evaluated. The results indicated that the retention of racemic acids on both CSPs is mainly dependent on the hydrogen bonding interaction between the acid proton of the carboxyl moiety of the analyte and the carbonyl oxygen of the carbamate moiety of the CSP. The chiral recognition mechanism for Chiralpak AD involves: (1) the formation of transient diastereomeric analyte-CSP complexes through hydrogen bonding interactions between the carboxyl and the carbamate moieties of the acid and CSP, respectively; (2) stabilization of these complexes by insertion of the aromatic portion of the analytes into the chiral cavities of the CSP, as well as pi-pi, dipole-dipole, and additional hydrogen bonding interactions between analyte and CSP; and (3) chiral discrimination between enantiomer analytes arising from the additional hydrogen bond between analyte and CSP. For Chiralcel OD, the chiral recognition mechanisms involve: (1) the formation of transient diastereomeric analyte-CSP complexes through hydrogen bonding interactions between the carboxyl and the carbamate moieties of the acid and CSP, respectively; (2) stabilization of these complexes by insertion of the aromatic portion of the analytes into the chiral cavities of the CSP, as well as pi-pi and dipole-dipole interactions between analyte and CSP; and (3) chiral discrimination due to: (a) the difference in the steric fit of enantiomers into the chiral cavity of the CSP (entropy controlled); and (b) dipole-dipole or p-p interactions between enantiomer analytes and CSP (enthalpy controlled). Chromatographic and quantitative thermodynamic data showed that there are at least two different chiral recognition… Advisors/Committee Members: McNair, Harold M. (committeechair), McNair, Harold M. (committee member), Anderson, Mark R. (committee member), Glanville, James O. (committee member), Long, Gary L. (committee member), Taylor, Larry T. (committee member), Kazakevich, Yuri V. (committee member).

Subjects/Keywords: chiral stationary phases; profens; Chiral separation

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APA (6^th Edition):

Cabusas, M. E. Y. I. (1998). Chiral Separations on HPLC Derivatized Polysaccharide CSPs: Temperature, Mobile Phase and Chiral Recognition Mechanism Studies. (Doctoral Dissertation). Virginia Tech. Retrieved from http://hdl.handle.net/10919/30426

Chicago Manual of Style (16^th Edition):

Cabusas, Maria Elena Ybarbia III. “Chiral Separations on HPLC Derivatized Polysaccharide CSPs: Temperature, Mobile Phase and Chiral Recognition Mechanism Studies.” 1998. Doctoral Dissertation, Virginia Tech. Accessed January 18, 2021. http://hdl.handle.net/10919/30426.

MLA Handbook (7^th Edition):

Cabusas, Maria Elena Ybarbia III. “Chiral Separations on HPLC Derivatized Polysaccharide CSPs: Temperature, Mobile Phase and Chiral Recognition Mechanism Studies.” 1998. Web. 18 Jan 2021.

Vancouver:

Cabusas MEYI. Chiral Separations on HPLC Derivatized Polysaccharide CSPs: Temperature, Mobile Phase and Chiral Recognition Mechanism Studies. [Internet] [Doctoral dissertation]. Virginia Tech; 1998. [cited 2021 Jan 18]. Available from: http://hdl.handle.net/10919/30426.

Council of Science Editors:

Cabusas MEYI. Chiral Separations on HPLC Derivatized Polysaccharide CSPs: Temperature, Mobile Phase and Chiral Recognition Mechanism Studies. [Doctoral Dissertation]. Virginia Tech; 1998. Available from: http://hdl.handle.net/10919/30426

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