Browsing by Subject "forensic science"

Now showing 1 - 7 of 7
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    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 Science
    The 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.
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    Estimation of the number of contributors of theoretical mixture profiles based on allele counting: Does increasing the number of loci increase success rate of estimates?
    (Elsevier, 2018-03) Dembinski, Gina M.; Sobieralski, Carl; Picard, Christine J.; Biology, School of Science
    DNA mixtures are more frequently encountered in casework due to increased kit sensitivity, protocols with increased cycle number, and requests for low copy number DNA samples to be tested. Generally, the first step in mixture interpretation is determining the number of contributors, with the most common approach of maximum allele count. Although there are previous studies regarding the accuracy of this approach, none have evaluated the accuracy with the newly expanded U.S. core STR loci. In this work, 4,976,355 theoretical mixture combinations were generated with the PowerPlex® Fusion 6C system which includes 23 autosomal STR loci and three Y-STR loci. The number of contributors could be correctly assumed for 100% two-person and 99.99% three-person mixtures, whereas, four-, five-, and six-person mixtures were correctly assumed in 89.7%, 57.3%, and 7.8% of mixtures, respectively. Y-STR analysis showed the 3 Y-STR markers are only accurate for two-person male mixtures (96.7%). This work demonstrates that maximum allele count using the expanded U.S. core loci is not much improved from previous smaller panels, reiterating that this method is not as accurate beyond three contributors.
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    Formation and identification of novel derivatives of primary amine and zwitterionic drugs
    (Elsevier, 2018-08) Ash, Jordan; Hickey, Logan; Goodpaster, John V.; Chemistry and Chemical Biology, School of Science
    Gas chromatography-mass spectrometry (GC–MS) is a “workhorse” in the analysis of controlled substances in forensic laboratories. However, many drugs are not amenable to GC–MS due to thermal instability, non-ideal interactions in the column, or both. To improve the suitability of a molecule for analysis by GC–MS, derivatization can be employed. Derivatization replaces a labile hydrogen in the analyte molecule with a more stable functional group. In this paper, three different derivatization agents were tested for effectiveness with two classes of drugs: primary amines (i.e., amphetamine and 2C-I) and zwitterions (i.e., gabapentin, lorazepam, vigabatrin, pregabalin, and clorazepate). Trifluoroacetic anhydride (TFAA) was used as an acylating agent and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) was used as a silylating agent. Dimethylformamide-dimethyl acetal (DMF-DMA), which has not been previously used for derivatization of drugs, was used as an alkylating agent. DMF-DMA was found to form dimethylaminomethylene derivatives with several primary amines and zwitterions. Amphetamine, 2C-I, gabapentin, and lorazepam were all detected in their underivatized form but generally suffered from peak asymmetry and band broadening. Derivatization resulted in drastic improvements in their chromatographic behavior. Vigabatrin, clorazepate and pregabalin were not detectable in their underivatized form. However, the trimethylsilyl (TMS) derivative of clorazepate was readily detected by GC–MS, as were the TMS and trifluoroacetyl (TFA) derivatives of vigabatrin. Derivatization of pregabalin was not successful, resulting in multiple chromatographic peaks with each derivatization agent. The mass spectra of several derivatives were not found in commercially available mass spectral databases. Hence, those spectra are reported here with interpretation of their fragmentation.
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    Improving the confidence of “questioned versus known” fiber comparisons using microspectrophotometry and chemometrics
    (Elsevier, 2016-11) Sauzier, Georgina; Reichard, Eric; van Bronswijk, Wilhelm; Lewis, Simon W.; Goodpaster, John V.; Department of Chemistry and Chemical Biology, School of Science
    Microspectrophotometry followed by chemometric data analysis was conducted on pairs of visually similar blue acrylic fibers, simulating the “questioned versus known” scenarios often encountered in forensic casework. The relative similarity or dissimilarity of each pair was determined by employing principal component analysis, discriminant analysis and Fisher’s exact test. Comparison of fibers from within each set resulted in a correct inclusion result in 10 out of 11 scenarios, with the one false exclusion attributed to a lack of reproducibility in the spectra. Comparison of fibers from different sets resulted in a correct exclusion result in 108 of 110 scenarios, with two sets that shared identical dye combinations being indistinguishable. Although the presented methods are not infallible, they may nonetheless provide a path forward for forensic fiber examiners that has a more scientifically rigorous basis on which to support their findings in a court of law.
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    Mapping smokeless powder residue on PVC pipe bomb fragments using total vaporization solid phase microextraction
    (Elsevier, 2017-07) Bors, Dana; Goodpaster, John V.; Department of Chemistry & Chemical Biology, School of Science
    Quantitating post-blast explosive residue is not a common practice in crime labs as it is typically not legally relevant. There is value in quantitation, however, if the distribution of residues on Improvised Explosive Devices (IEDs) can help guide future sample collection and/or method development. Total vaporization solid phase microextraction gas chromatography mass spectrometry (TV-SPME/GC/MS) was used to quantify residues of double-base smokeless powder (DBSP), which includes nitroglycerin (NG), diphenylamine (DPA), and ethyl centralite (EC) on post-blast PVC pipe bomb fragments. The analytical method could separate the three constituents in under 5 min with a detection limit under 1 ppb, which demonstrates high throughput while maintaining high sensitivity. The method was optimized for nitroglycerin, as it is the most indicative of DBSP. The average mass of nitroglycerin recovered from an entire PVC device was 1.0 mg. The average mass of diphenylamine recovered was much lower (24 μg) and only one device had detectable levels of EC. The typical concentration of NG on any given fragment was approximately 15–30 ppm (μg NG/g fragment). However, there was no correlation between the mass of a fragment and the mass of residue upon it. Instead, the residue was distributed such that the highest concentration of residues was found on end cap fragments.
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    Microspectrophotometric Analysis of Yellow Polyester Fiber Dye Loadings with Chemometric Techniques
    (Elsevier, 2017-03) Reichard, Eric J.; Bartick, Edward G.; Morgan, Stephen L.; Goodpaster, John V.; Chemistry and Chemical Biology, School of Science
    Microspectrophotometry is a quick, accurate, and reproducible method to compare colored fibers for forensic purposes. Applying chemometric techniques to spectroscopic data can provide valuable information, especially when looking at a complex dataset. In this study, background subtracted and normalized visible spectra from ten yellow polyester exemplars dyed with different concentrations of the same dye ranging from 0.1% to 3.5% (w/w), were analyzed by agglomerative hierarchical clustering (AHC), principal component analysis (PCA), and discriminant analysis (DA). Systematic changes in the wavelength of maximum absorption, peak shape and signal-to-background ratio were noted as dye loading increased. In general, classifying the samples into ten groups (one for each exemplar) had poor accuracy (i.e., 51%). However, classification was much more accurate (i.e., 96%) using three classes of fibers that were identified by AHC as having low (0.10–0.20 wt%), medium (0.40–0.75 wt%), and high (1.5–3.5 wt%) dye loadings. An external validation with additional fibers and data generated by independent analysts confirmed these findings. Lastly, it was also possible to discriminating pairs of exemplars with small differences in dye loadings as a simulation of questioned (Q) versus known (K) comparisons.