Browsing by Subject "Gas chromatography"

Now showing 1 - 5 of 5
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    A systematic study of the absorbance of the nitro functional group in the vacuum UV region
    (Elsevier, 2021-11-15) Cruse, Courtney A.; Goodpaster, John V.; Chemistry and Chemical Biology, School of Science
    The nitro functional group (NO) features strongly in compounds such as explosives, pharmaceuticals, and fragrances. However, its gas phase absorbance characteristics in the vacuum UV region (120-200 nm) have not been systematically studied. Gas chromatography/vacuum UV spectroscopy (GC/VUV) was utilized to study the gas phase VUV spectra of various nitrated compounds (e.g., nitrate esters (-R-O-NO), nitramines (R-N-NO), nitroaromatics (Ar-NO), and nitroalkanes (R-NO)). The nitro absorption maximum appeared over a wide range (170-270 nm) and its wavelength and intensity were highly dependent upon the structure of the rest of the molecule. For example, the nitroalkanes exhibited a trend in that the ratio of the relative absorption intensity between these two absorption features between the alkyl group (<150 nm) and the nitro group (200 nm) increases as the molecular weight increases. It was observed that the addition of multiple nitro functional groups on benzene or toluene resulted in an increase in intensity and blue shift from approximately 240 nm-210 nm. Nitrate esters exhibited an absorption between 170 nm and 210 nm and absorbance increased with increasing nitrogen content. The relative diversity of the spectra obtained was analyzed by Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA). These calculations revealed that the spectra of all the compounds analyzed could be reliably differentiated without any misclassifications.
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    Automated Derivatization and Identification of Controlled Substances via Total Vaporization Solid Phase Microextraction (TV-SPME) and Gas Chromatography/Mass Spectrometry (GC/MS)
    (U.S. Department of Justice, Office of Justice Programs, 2018-11) Goodpaster, John V.
    The hypothesis tested was that Total Vaporization - Solid Phase Microextraction (TV-SPME) will offer greater sensitivity than traditional liquid injection for controlled substances. In addition, TV-SPME was easily adapted to include either a pre-extraction or a post-extraction on-fiber derivatization step for thermally labile species. Project results were promising for all drug classes that were analyzed successfully by on-fiber derivatization as solutions. This discovery greatly improves the utility of the technique, since controlled substances are most often encountered in their solid forms in forensic science laboratories. The application of this technique to beverage samples and solid drug powders is of most interest, since these applications involve a significant decrease in sample preparation. Although not ideal for all analytes, TV-SPME with on-fiber derivatization could be a powerful technique for amine and hydroxylamine controlled substances, as well as GHB. The technique could increase analyst efficiency by reducing sample preparation time for these types of analytes. Thus, the main results of this project are a set of optimized derivatization methods that can be used in liquid injection or TV-SPfsME. This approach offers the possibility of automated sampling and derivatization for a wide variety of thermally labile compounds and the analysis of compounds that require no derivatization. Project design and methods are described. 4 figures and 1 table
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    Characterization of a fatty acid elongase condensing enzyme by site-directed mutagenesis and biochemical analysis
    (2014) Hernandez-Buquer, Selene; Long, Eric C. (Eric Charles); Blacklock, Brenda J.; Li, Lei
    Fatty acid elongation is the extension of de novo synthesized fatty acids through a series of four reactions analogous to those of fatty acid synthase. ELOs catalyze the first reaction in the elongation pathway through the condensation of an acyl group with a two carbon unit derived from malonyl-CoA. This study uses the condensing enzyme, EloA, from the cellular slime mold, Dictyostelium discoideum as a model for the family of ELOs. EloA has substrate specificity for monounsaturated and saturated C16 fatty acids and catalyzes the elongation of 16:1Δ9 to 18:1Δ11. Site-directed mutagenesis was used to change residues highly conserved among the ELO family to examine their potential role in the condensation reaction. Mutant EloAs were expressed in yeast and fatty acid methyl esters prepared from total cellular lipids were analyzed by gas chromatography/mass spectrometry. Sixteen out of twenty mutants had a decrease in 18:1Δ11 production when compared to the wild-type EloA with little to no activity observed in ten mutants, four mutants had within 20% of wild-type activity, and six mutants had 10-60% of wild-type activity. Immunoblot studies using anti-EloA serum were used to determine if the differences in elongation activity were related to changes in protein expression for each mutant. Analysis of immunoblots indicated that those mutants with little to no activity, with the exception of T130A and Q203A, had x comparable protein expression to the wild-type. Further research included the solubilization of the His6-ELoA fusion protein and preliminary work toward the isolation of the tagged protein and the use of a radiolabeled condensation assay to determine the activity of the eluted protein. Preliminary results indicated that the protein was solubilized but the eluted protein showed no activity when examined by a condensation assay. The work presented here contributes to a better understanding of the role of certain amino acid residues in the activity of EloA and serves as a stepping-stone for future EloA isolation work.
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    Quantitative analysis of smokeless powder particles in post-blast debris via gas chromatography/vacuum ultraviolet spectroscopy (GC/VUV)
    (Wiley, 2022) Reavis, Madison; Goodpaster, John; Forensic and Investigative Sciences, School of Science
    Forensic analysis of smokeless powder particles recovered from the debris of an improvised explosive device can provide information about the type of smokeless powder used and can aid investigation efforts. In this study, quantitative methods were used to yield information about the difference in the chemical composition of the particles pre‐ and post‐blast. The technique, gas chromatography/vacuum ultraviolet spectroscopy (GC/VUV), was able to quantify nitroglycerin, 2,4‐dinitrotoluene, diphenylamine, ethyl centralite, and di‐n‐butyl phthalate in pre‐ and post‐blast smokeless powder particles using heptadecane as an internal standard. Post‐blast debris was obtained via controlled explosions with assistance from the Indiana State Police Bomb Squad. Two galvanized steel and two polyvinyl chloride pipe bombs were assembled. Two devices contained single‐base smokeless powder and two contained double‐base smokeless powder. 2,4‐dinitrotoluene and diphenylamine were successfully quantified in the single‐base smokeless powder post‐blast debris while nitroglycerin, diphenylamine, and ethyl centralite were successfully quantified in the double‐base smokeless powder post‐blast debris. Compounds were detected at concentrations as low as 9 μg of 2,4‐dinitrotoluene per mg, <3 μg of diphenylamine per mg, 131 μg of nitroglycerin per mg, and <3 μg of ethyl centralite per mg. Concentration changes between pre‐ and post‐blast smokeless powder particles were determined as well as microscopic differences between pre‐ and post‐blast debris for both smokeless powders in all devices. To our knowledge, this is the first use of GC/VUV for the quantification of explosives.
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    Tracking the Progression of Triple Negative Mammary Tumors over Time by Chemometric Analysis of Urinary Volatile Organic Compounds
    (Cancers, 2021-01) Woollam, Mark; Wang, Luqi; Grocki, Paul; Liu, Shengzhi; Siegel, Amanda P.; Kalra, Maitri; Goodpaster, John V.; Yokota, Hiroki; Agarwal, Mangilal
    Previous studies have shown that volatile organic compounds (VOCs) are potential biomarkers of breast cancer. An unanswered question is how urinary VOCs change over time as tumors progress. To explore this, BALB/c mice were injected with 4T1.2 triple negative murine tumor cells in the tibia. This typically causes tumor progression and osteolysis in 1–2 weeks. Samples were collected prior to tumor injection and from days 2–19. Samples were analyzed by headspace solid phase microextraction coupled to gas chromatography–mass spectrometry. Univariate analysis identified VOCs that were biomarkers for breast cancer; some of these varied significantly over time and others did not. Principal component analysis was used to distinguish Cancer (all Weeks) from Control and Cancer Week 1 from Cancer Week 3 with over 90% accuracy. Forward feature selection and linear discriminant analysis identified a unique panel that could identify tumor presence with 94% accuracy and distinguish progression (Cancer Week 1 from Cancer Week 3) with 97% accuracy. Principal component regression analysis also demonstrated that a VOC panel could predict number of days since tumor injection (R2 = 0.71 and adjusted R2 = 0.63). VOC biomarkers identified by these analyses were associated with metabolic pathways relevant to breast cancer.