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DISCRIMINATION OF AUTOMOBILE CARPET FIBERS USING MULTIPLE ANALYTICAL TECHNIQUES AND THE SUBSEQUENT CREATION OF A SEARCHABLE DATABASE.
Title
DISCRIMINATION OF AUTOMOBILE CARPET FIBERS USING MULTIPLE ANALYTICAL TECHNIQUES AND THE SUBSEQUENT CREATION OF A SEARCHABLE DATABASE.
Creator
Dorrien, Derek, Sigman, Michael, University of Central Florida
Abstract / Description
Forensic fiber examination is an important part of trace evidence analysis. Fibers may be recovered from a crime scene that could link a particular suspect to the scene. Clothing fibers are most frequently encountered but automobile carpeting fibers may also be recovered. An understanding of the frequency of occurrence and the discrimination power of different analytical techniques is needed in order to better establish the evidentiary value of automobile carpet fiber evidence. Seventy-five...
Show moreForensic fiber examination is an important part of trace evidence analysis. Fibers may be recovered from a crime scene that could link a particular suspect to the scene. Clothing fibers are most frequently encountered but automobile carpeting fibers may also be recovered. An understanding of the frequency of occurrence and the discrimination power of different analytical techniques is needed in order to better establish the evidentiary value of automobile carpet fiber evidence. Seventy-five automobile carpet fiber samples were analyzed using a series of techniques ranging from nondestructive to destructive. These techniques included polarized light microscopy, fluorescence microscopy, microspectrophotometry, Fourier-transform infrared spectroscopy, microtomy (cross section analysis), dye extraction and liquid chromatography-mass spectrometry. Based on the information obtained from these techniques an overall discrimination of 98.02% was calculated. Only 55 of 2775 pairwise comparisons were indistinguishable. The information was subsequently entered into a searchable database for general public use.
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Date Issued
2006
Identifier
CFE0001483, ucf:47103
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0001483
Forensic Application of Chemometric Analysis to Visible Absorption Spectra Collected from Dyed Textile Fibers
Title
Forensic Application of Chemometric Analysis to Visible Absorption Spectra Collected from Dyed Textile Fibers.
Creator
Flores, Alejandra, Sigman, Michael, Yestrebsky, Cherie, Campiglia, Andres, Chumbimuni Torres, Karin, Ni, Liqiang, University of Central Florida
Abstract / Description
Forensic analysis of evidence consists of the comparison of physical, spectroscopic, or chemical characteristics of a questioned sample to a set of knowns. Currently, decisions as to whether or not the questioned sample can be associated or grouped with the knowns are left up to the discretion of the forensic analyst. The implications of these outcomes are presented as evidence to a jury in a court of law to determine if a defendant is guilty of committing a crime or not. Leading up to, and...
Show moreForensic analysis of evidence consists of the comparison of physical, spectroscopic, or chemical characteristics of a questioned sample to a set of knowns. Currently, decisions as to whether or not the questioned sample can be associated or grouped with the knowns are left up to the discretion of the forensic analyst. The implications of these outcomes are presented as evidence to a jury in a court of law to determine if a defendant is guilty of committing a crime or not. Leading up to, and since, the publication of the National Academy of Sciences (NAS) report entitled (")Strengthening Forensic Science in the United States: A Path Forward,(") the inadequacies of allowing potentially biased forensic opinion to carry such weight in the courtroom have been unmasked. This report exposed numerous shortcomings in many areas of forensic science, but also made recommendations on how to fortify the discipline. The main suggestions directed towards disciplines that analyze trace evidence include developing error rates for commonly employed practices and evaluating method reliability and validity.This research focuses on developing a statistical method of analysis for comparing visible absorption profiles collected from highly similarly colored textile fibers via microspectrophotometry (MSP). Several chemometric techniques were applied to spectral data and utilized to help discriminate fibers beyond the point where traditional methods of microscopical examination may fail. Because a dye's chemical structure dictates the shape of the absorption profile, two fibers dyed with chemically similar dyes can be very difficult to distinguish from one another using traditional fiber examination techniques. The application of chemometrics to multivariate spectral data may help elicit latent characteristics that may aid in fiber discrimination.The three sample sets analyzed include dyed fabric swatches (three pairs of fabrics were dyed with chemically similar dye pairs), commercially available blue yarns (100% acrylic), and denims fabrics (100% cotton). Custom dyed swatches were each dyed uniformly with a single dye whereas the dye formulation for both the yarns and denims is unknown. As a point for study, spectral comparisons were performed according to the guidelines published by the Standard Working Group for Materials Analysis (SWGMAT) Fiber Subgroup based on visual analysis only. In the next set of tests, principal components analysis (PCA) was utilized to reduce the dimensionality of the large multivariate data sets and to visualize the natural groupings of samples. Comparisons were performed using the resulting PCA scores where group membership of the questioned object was evaluated against the known objects using the score value as the distance metric. Score value is calculated using the score and orthogonal distances, the respective cutoff values based on a quantile percentage, and an optimization parameter, ?. Lastly, likelihood ratios (LR) were generated from density functions modelled from similarity values assessing comparisons between sample population data. R code was written in-house to execute all method of fiber comparisons described here. The SWGMAT method performed with 62.7% accuracy, the optimal accuracy rate for the score value method was 75.9%, and the accuracy rates for swatch-yarn and denim comparisons, respectively, are 97.7% and 67.1% when the LR method was applied.
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Date Issued
2015
Identifier
CFE0005613, ucf:50212
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005613
ROOM TEMPERATURE FLUORESCENCE SPECTROSCOPY AS A TOOL FOR THE FORENSIC TRACE ANALYSIS OF TEXTILE FIBERS
Title
ROOM TEMPERATURE FLUORESCENCE SPECTROSCOPY AS A TOOL FOR THE FORENSIC TRACE ANALYSIS OF TEXTILE FIBERS.
Creator
Rex, Matthew, Campiglia, Andres, University of Central Florida
Abstract / Description
ABSTRACT Trace textile fiber evidence is found at numerous crime scenes and plays an important role in linking a suspect to the respective scene. Several methods currently exist for the analysis of trace fiber evidence. Microscopy provides information regarding the fibers material, color and weave. For more detailed chemical analysis chromatographic methods are employed and for discrimination between dyes, liquid chromatography coupled with mass spectrometry (LC-MS) is currently the method...
Show moreABSTRACT Trace textile fiber evidence is found at numerous crime scenes and plays an important role in linking a suspect to the respective scene. Several methods currently exist for the analysis of trace fiber evidence. Microscopy provides information regarding the fibers material, color and weave. For more detailed chemical analysis chromatographic methods are employed and for discrimination between dyes, liquid chromatography coupled with mass spectrometry (LC-MS) is currently the method providing the most discrimination. These methods have primarily focused on the dyes used to color the fibers and have not investigated other components that can potentially discriminate among fibers. This dissertation deals with investigations into the fluorescence of the fiber dyes, (contaminants?) and the fibers themselves, as well as methodology for discriminating between fibers using fluorescence. Initial systematic analysis was conducted on dye standards and extracts taken from fibers colored with the respective dyes of interest. Absorbance, excitation and fluorescence spectra were compared between standards and extracts to determine the optimal area of the fiber to investigate: dyes, fluorescent impurities or the whole fiber. High performance liquid chromatography investigations were performed to give detailed information on the number of dye and fluorescent components present in extracts. Our investigations then focused on the best room-temperature fluorescence (RTF) data format for analysis and discrimination of fiber samples. An excitation emission matrix (EEM) was found to give the greatest amount of spectral information and provide the highest level of discrimination. Successful discrimination between non similar and similar fibers was achieved with the aid of Chemometric analysis. The level of discrimination obtained via RTF-EEM spectroscopy was sufficient to differentiate among fibers obtained from two separate cloths of the same material and colored with the same dye reagent. Final studies deal with examining exposure of the fiber to various environmental contaminants. Clothing fibers are typically exposed to myriad numbers of contaminants, from food stains to cigarette smoke. The challenge then becomes detecting fluorescence signals from trace amounts of these environmental contaminants. We demonstrate the detection and classification of polycyclic aromatic hyrdrocarbons (PAH) present on fibers after exposure to cigarette smoke. This dissertation also investigates the change in fluorescence emission after laundering fibers numerous times. The main drawback of chemical analysis of fibers is the destructive nature of the methods. To extract a dye or contaminant from a fiber essentially destroys the evidence. This leaves the investigator without their original sample in the courtroom. This also provides a finite amount of sample for testing and analysis. This is true of chromatographic methods and for the method detailed in this dissertation which makes use of extracts taken from fiber samples. Lastly, we propose an instrumental setup coupling a microscope to a spectrofluorimeter for the purpose of taking EEM directly from a fiber sample. This setup makes use of the superior optics of the microscope for focusing excitation light onto the fiber sample. Initial studies have been performed on extracts from a single textile fiber and EEM collected from said fiber.
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Date Issued
2009
Identifier
CFE0002833, ucf:48084
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0002833
Non-Destructive Analysis of Trace Textile Fiber Evidence via Room-Temperature Fluorescence Spectrocopy
Title
Non-Destructive Analysis of Trace Textile Fiber Evidence via Room-Temperature Fluorescence Spectrocopy.
Creator
Appalaneni, Krishnaveni, Campiglia, Andres, Belfield, Kevin, Sigman, Michael, Yestrebsky, Cherie, Schulte, Alfons, University of Central Florida
Abstract / Description
Forensic fiber evidence plays an important role in many criminal investigations. Non-destructive techniques that preserve the physical integrity of the fibers for further court examination are highly valuable in forensic science. Non-destructive techniques that can either discriminate between similar fibers or match a known to a questioned fiber - and still preserve the physical integrity of the fibers for further court examination - are highly valuable in forensic science. When fibers cannot...
Show moreForensic fiber evidence plays an important role in many criminal investigations. Non-destructive techniques that preserve the physical integrity of the fibers for further court examination are highly valuable in forensic science. Non-destructive techniques that can either discriminate between similar fibers or match a known to a questioned fiber - and still preserve the physical integrity of the fibers for further court examination - are highly valuable in forensic science. When fibers cannot be discriminated by non-destructive tests, the next reasonable step is to extract the questioned and known fibers for dye analysis with a more selective technique such as high-performance liquid chromatography (HPLC) and/or gas chromatography-mass spectrometry (GC-MS). The common denominator among chromatographic techniques is to primarily focus on the dyes used to color the fibers and do not investigate other potential discriminating components present on the fiber. Differentiating among commercial dyes with very similar chromatographic behaviors and almost identical absorption spectra and/or fragmentation patterns is a challenging task.This dissertation explores a different aspect of fiber analysis as it focuses on the total fluorescence emission of fibers. In addition to the contribution of the textile dye (or dyes) to the fluorescence spectrum of the fiber, we investigate the contribution of intrinsic fluorescence impurities (-) i.e. impurities imbedded into the fibers during fabrication of garments - as a reproducible source of fiber comparison. Differentiation of visually indistinguishable fibers is achieved by comparing excitation-emission matrices (EEMs) recorded from single textile fibers with the aid of a commercial spectrofluorimeter coupled to an epi-fluorescence microscope. Statistical data comparison was carried out via principal component analysis. An application of this statistical approach is demonstrated using challenging dyes with similarities both in two-dimensional absorbance spectra and in three dimensional EEM data. High accuracy of fiber identification was observed in all the cases and no false positive identifications were observed at 99% confidence levels.
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Date Issued
2013
Identifier
CFE0004808, ucf:49740
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004808