Browsing by Author "Goodpaster, John V."
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Item 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 ScienceThe 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.Item Advances in Gas Chromatography and Vacuum UV Spectroscopy: Applications to Fire Debris Analysis & Drugs of Abuse(2020-12) Roberson, Zackery Ray; Goodpaster, John V.; Manicke, Nicholas E.; Webb, Ian K.; Laulhé, SébastienIn forensic chemistry, a quicker and more accurate analysis of a sample is always being pursued. Speedy analyses allow the analyst to provide quick turn-around times and potentially decrease back-logs that are known to be a problem in the field. Accurate analyses are paramount with the futures and lives of the accused potentially on the line. One of the most common methods of analysis in forensic chemistry laboratories is gas chromatography, chosen for the relative speed and efficiency afforded by this method. Two major routes were attempted to further improve on gas chromatography applications in forensic chemistry. The first route was to decrease separation times for analysis of ignitable liquid residues by using micro-bore wall coated open-tubular columns. Micro-bore columns are much shorter and have higher separation efficiencies than the standard columns used in forensic chemistry, allowing for faster analysis times while maintaining the expected peak separation. Typical separation times for fire debris samples are between thirty minutes and one hour, the micro-bore columns were able to achieve equivalent performance in three minutes. The reduction in analysis time was demonstrated by analysis of ignitable liquid residues from simulated fire debris exemplars. The second route looked at a relatively new detector for gas chromatography known as a vacuum ultraviolet (VUV) spectrophotometer. The VUV detector uses traditional UV and far-ultraviolet light to probe the pi and sigma bonds of the gas phase analytes as well as Rydberg traditions to produce spectra that are nearly unique to a compound. Thus far, the only spectra that were not discernable were from enantiomers, otherwise even diastereomers have been differentiated. The specificity attained with the VUV detector has achieved differentiation of compounds that mass spectrometry, the most common detection method for chromatography in forensic chemistry labs, has difficulty distinguishing. This specificity has been demonstrated herein by analyzing various classes of drugs of abuse and applicability to “real world” samples has been demonstrated by analysis of de-identified seized samples.Item Advances in Gas Chromatography, Thermolysis, Mass Spectrometry, and Vacuum Ultraviolet Spectrometry(2021-05) Rael, Ashur; Goodpaster, John V.; Manicke, Nicholas E.; Naumann, Christoph A.; Minto, Robert E.In the area of forensic chemistry, improved or new analysis methods are continually being investigated. One common and powerful technique used in forensic chemistry is wall-coated open-tubular column (WCOT) gas chromatography with electron ionization single quadrupole mass spectrometry (GC-MS). Improvements to and effectiveness of alternatives to this instrumental platform were explored in an array of parallel inquiries. The areas studied included the column for the chromatographic separation, the universal detection method employed, and the fragmentation method used to enhance molecular identification. Superfine-micropacked capillary (SFµPC) columns may provide an alternative to commercial packed GC columns and WCOT GC columns that combines the benefits of the larger sample capacity of packed columns and the benefits of the excellent separation capabilities and mass spectrometry (MS) flow rate compatibility of WCOT columns. SFµPC columns suffer from high inlet pressure requirements and prior reported work has required specialized instrumentation for their use. Fabrication of and chromatography with SFµPC GC columns was successfully achieved with typical GC-MS instrumentation and within the flow rate limit of a MS. Additionally, the use of higher viscosity carrier gasses was demonstrated to reduce the required inlet pressure for SFµPC GC columns. Recently, a new vacuum ultraviolet spectrometer (VUV) universal detector has been commercialized for GC. The ability of VUV detectors to acquire absorbance spectra from 125 nm to 430 nm poses a potential alternative to MS. As such, GC-VUV provides an exciting potential alternative approach to achieving excellent quantitative and qualitative analysis across a wide range of analytes. The performance of VUV and MS detectors for forensic analysis in terms of quantitative and qualitative analysis was compared. Analysis of alkylbenzenes in ignitable liquids was explored, which can be important evidence from suspected arson fires and are difficult to differentiate with MS. The VUV detector was found to have superior specificity and comparable sensitivity to the MS detector in scan mode. Addition of thermolysis (Th) as an orthogonal fragmentation pathway provides the opportunity to increase the differences between MS fragmentation patterns. Fragmentation has been widely established to aid in identification of molecules with MS by providing characteristic fragments at characteristic relative abundances. However, molecules with very similar structures do not result in sizable spectral differences in all cases with typical MS fragmentation techniques. A series of Th units were fabricated and integrated into GC-Th-MS instruments. Th-MS was conducted with the thermally labile nitrate esters across a range of instrumentation and thermal conditions.Item Advances in Solid Phase Microextraction for the Analysis of Volatile Compounds in Explosives, Tire Treatments, and Entomological Specimens(2016-05) Kranz, William D.; Goodpaster, John V.; Manicke, Nick; Sardar, Rajesh; Picard, Christine Johanna; Long, Eric C.Solid phase micro-extraction is a powerful and versatile technique, well-suited to the analysis of numerous samples of forensic interest. The exceptional sensitivity of the SPME platform, combined with its adaptability to traditional GC-MS systems and its ability to extract samples with minimal work-up, make it appropriate to applications in forensic laboratories. In a series of research projects, solid phase micro-extraction was employed for the analysis of explosives, commercial tire treatments, and entomological specimens. In the first project, the volatile organic compounds emanating from two brands of pseudo-explosive training aids for use in detector dog imprinting were determined by SPME-GC-MS, and the efficacy of these training materials was tested in live canine trials. In the second project, the headspace above various plasticizers was analyzed comparative to that of Composition C-4 in order to draw conclusions about the odor compound, 2- ethyl-1-hexnaol, with an eye toward the design of future training aids. In the third, automobile tires which had participated in professional race events were analyzed for the presence of illicit tire treatments, and in the fourth, a novel SPME-GC-MS method was developed for the analysis of blowfly (Diptera) liquid extracts. In the fifth and final project, the new method was put to the task of performing a chemotaxonomic analysis on pupa specimens, seeking to chemically characterize them according to their age, generation, and species.Item 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 tableItem Beam profile characterization of light-emitting-diode curing units and its effect on polymerization of a resin-matrix composite(2017) AlZain, Afnan Omar; Platt, Jeffrey A.; Chu, Tien-Min G.; Bottino, Marco C.; Hara, Anderson T.; Goodpaster, John V.; Roulet, Jean-FrancoisThe general aim of this study was to investigate the influence of the localized irradiance beam profiles from multiple light-emitting-diode (LED) light-curing units (LCUs) on the polymerization pattern within a resin-matrix composite (RMC). Irradiance beam profiles were generated from one quartz-tungsten-halogen and various single and multiple emission peak LED LCUs using a camera-based beam profiler system combined with LCU power measurements obtained using an integrating sphere/spectrometer assembly. The influence of distance on irradiance, radiant exposure (RE) and degree of conversion (DC) on the top and bottom surfaces of a RMC increment, using various LCUs, at two clinically relevant distances was investigated. Molar absorptivity of the photoinitiators present in the nano-hybrid RMC (Tetric EvoCeram bleaching shade-XL) assessed was using UV-spectrophotometry. The correlation among irradiance, RE and DC was explored. A mapping approach was used to investigate DC, microhardness and cross-link density (CLD) within 5×5×2 mm specimens at various depths; top, 0.5, 0.7, 0.9, 1.1, 1.3,1.5 mm and bottom. The localized irradiance correlation with its corresponding DC, microhardness and CLD was explored, and localized DC correlation with microhardness was assessed. The DC was measured using micro-Raman spectroscopy, and CLD was assessed by an ethanol-softening method (%KHN reduction) using an automated microhardness tester. Molar absorptivity of diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide was 20-fold higher than camphorquinone. Non-uniform LCU beam profiles caused localized polymerization discrepancies that were significant at specific depths and points within the specimens with respect to DC, microhardness and CLD, which did not follow a specific pattern regardless of the LCU or curing distance assessed. A moderate correlation was displayed among irradiance, RE and DC. The localized irradiance from the LCUs was weakly correlated with the corresponding DC, microhardness and CLD on the top surface of a RMC at both curing distances. The localized microhardness was moderately correlated with DC. In conclusion, polymerization within the RMC investigated was non-uniform and did not reflect the LCU irradiance pattern at the area assessed. Also, a mapping approach within the specimens provided a detailed polymerization pattern assessment occurring within a RMC increment. Therefore, the LCUs explored may potentially increase the risk of RMC fracture.Item Characterization of Automotive Paint Clear Coats by Ultraviolet Absorption Microspectrophotometry with Subsequent Chemometric Analysis(2010-10) Liszewski, Elisa A; Lewis, Simon W; Siegel, Jay A; Goodpaster, John V.Clear coats have been a staple in automobile paints for almost thirty years and are of forensic interest when comparing transferred and native paints. However, the ultraviolet (UV) absorbers in these paint layers are not typically characterized using UV microspectrophotometry, nor are the results studied using multivariate statistical methods. In this study, measurements were carried out by UV microspectrophotometry on 71 samples from American and Australian automobiles, with subsequent chemometric analysis of the absorbance spectra. Sample preparation proved to be vital in obtaining accurate absorbance spectra and a method involving peeling the clear coat layer and not using a mounting medium was preferred. Agglomerative hierarchical clustering indicated three main groups of spectra, corresponding to spectra with one, two, and three maxima. Principal components analysis confirmed this clustering and the factor loadings indicated that a substantial proportion of the variance in the data set originated from specific spectral regions (230–265 nm, 275–285 nm, and 300–370 nm). The three classes were well differentiated using discriminant analysis, where the cross-validation accuracy was 91.6% and the external validation accuracy was 81.1%. However, results showed no correlation between the make, model, and year of the automobiles.Item Chemical analysis of racing fuels using total vaporization and gas chromatography mass spectrometry (GC/MS)(RSC, 2016-05) Bors, Dana; Goodpaster, John V.; Chemistry and Chemical Biology, School of ScienceThe National Hot Rod Association (NHRA) is the governing body of North American drag racing. As a supervisory agency, NHRA monitors racing fuels for regulatory purposes and quality control. In this paper, total vaporization and mass spectrometry based methods were developed to analyze nitromethane-based and racing gasoline fuels. Total Vaporization Headspace gas chromatography mass spectrometry (TV-HS-GC/MS) was used to quatitate the amount of methanol in nitromethane fuels to verify that the methanol content was at least 10% (v/v). Total vaporization solid phase microextraction gas chromatography mass spectrometry (TV-SPME-GC/MS) was used to qualitatively identify racing gasoline components, which included isopentane, isooctane, toluene, and tetraethyllead.Item Classification Strategies for Fusing UV/visible Absorbance and Fluorescence Microspectrophotometry Spectra from Textile Fibers(Cambridge UP, 2018-08) Fuenffinger, Nathan; Goodpaster, John V.; Bartick, Edward G.; Morgan, Stephen L.; Chemistry and Chemical Biology, School of ScienceItem A Comprehensive Study of the Alteration of Ignitable Liquids by Weathering and Microbial Degradation(Wiley, 2018-01) Turner, Dee A.; Williams, Mary; Sigman, Michael A.; Goodpaster, John V.; Chemistry and Chemical Biology, School of ScienceThe differing effects of weathering and microbial degradation are described here in a comprehensive study that involved 50 different ignitable liquids from the Ignitable Liquids Database and Reference Collection. Examples of ignitable liquid residues from each of the main classes established by the American Society of Testing and Materials are presented. Weathering was accomplished via evaporation, whereas microbial degradation was carried out on soil at room temperature for periods of up to 21 days. Major trends included the rapid degradation of long n-alkanes and monosubstituted alkyl benzenes (e.g., toluene, ethylbenzene, and propylbenzene). Surprisingly, some longer branched alkanes (e.g., trimethyloctanes) were also susceptible to microbial attack. Although all ignitable liquids examined suffered at least to some extent from microbial degradation, gasoline, petroleum distillates, and oxygenates were the most susceptible. Isoparaffinic and naphthenic–paraffinic products were the most resistant to microbial degradation.