Tatiana Trejos
West Virginia University, Chemistry, Graduate Student
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Advances in technology provide forensic scientists with better tools to detect, to identify, and to individualize small amounts of trace evidence that have been left at a crime scene. The analysis of glass fragments can be useful in... more
Advances in technology provide forensic scientists with better tools to detect, to identify, and to individualize small amounts of trace evidence that have been left at a crime scene. The analysis of glass fragments can be useful in solving cases such as hit and run, burglaries, kidnappings, and bombings. The value of glass as "evidentiary material" lies in its inherent characteristics such as: (a) it is a fragile material that is often broken and hence commonly found in various types of crime scenes, (b) it can be easily transferred from the broken source to the scene, suspect, and/or victim, (c) it is relatively persistent, (d) it is chemically stable, and (e) it has measurable physical and chemical properties that can provide significant evidence of an association between the recovered glass fragments and the source of the broken glass. Forensic scientists have dedicated considerable effort to study and improve the detection and discrimination capabilities of analytical techniques in order to enhance the quality of information obtained from glass fragments. This article serves as a review of the developments in the application of both traditional and novel methods of glass analysis. The greatest progress has been made with respect to the incorporation of automated refractive index measurements and elemental analysis to the analytical scheme. Glass examiners have applied state-of-the-art technology including elemental analysis by sensitive methods such as ICPMS and LA-ICP-MS. A review of the literature regarding transfer, persistence, and interpretation of glass is also presented.
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This study reports the use of direct analysis in real time-mass spectrometry (DART-MS) for the detection of organic gunshot residues (OGSR) in a variety of matrices of interest for forensics, customs, and homeland security.
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The aims of evaluating forensic evidence are to provide a transparent, coherent, and unbiased opinion of the value of the evidence to fact‐finders. Measurements from glass evidence in a hit‐and‐run, for example, can help decide if a... more
The aims of evaluating forensic evidence are to provide a transparent, coherent, and unbiased opinion of the value of the evidence to fact‐finders. Measurements from glass evidence in a hit‐and‐run, for example, can help decide if a particular vehicle was involved in the accident. The evaluation involves the comparison of the physical, optical, and chemical properties of the glass recovered from the broken window with glass fragments suspected of originating from the window. A standard method (ASTM E2927‐16e1) describes a consensus‐based approach to sampling, sample preparation, quantitative analysis and “match” criterion for comparison of chemical properties. The result is a binary decision of either finding a difference in the elemental composition (exclusion) or a failure to exclude, based on elemental composition. This study demonstrates the utility of likelihood ratio (LR) calculations using novel datasets of glass samples of known manufacturing history. The LRs calculated from comparing glass manufactured at three different plants over relatively short periods (over 2‐6 weeks) range from very low values (LR ~ 10−3) when the glass are manufactured at different plants or manufactured weeks‐months apart in the same plant to very high values (LR ~ 103) when the glass samples are manufactured on the same day. Although the glass samples being compared may not originate from the same broken window source, they do exhibit chemical similarity within these lower and upper bounds and the LRs presented here, for the first time, closely correlate chemical relatedness to manufacturing history, specifically the time interval between production. The work presented here supports the use of the match criteria recommended within ASTM E2927‐16e1 and provides a data‐driven path forward to expand on the interpretation of glass using LRs.
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This study describes the use of single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) for the detection and classification of inorganic gunshot residue (IGSR) particles. To establish reliable... more
This study describes the use of single particle inductively coupled plasma time-of-flight mass spectrometry (spICP-TOFMS) for the detection and classification of inorganic gunshot residue (IGSR) particles. To establish reliable multi-element criteria to classify IGSR particles, leaded and lead-free IGSR reference materials were analyzed, and the elemental compositions of the individual particles were quantified. The results suggest that expanded element compositions may be used to classify IGSR particles via spICP-TOFMS compared to those used in conventional IGSR analysis using scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS). For spICP-TOFMS analysis of leaded IGSR particles, classification may be based on the presence of lead (Pb), antimony (Sb), and barium (Ba) just as in SEM-EDS; however, additional particle types, such as lead-copper (Pb–Cu) particles, contribute significantly (∼30%) to the leaded IGSR particle population. In lead-free IGSR particles,...
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Abstract The identification of counterfeit pharmaceutical packaging is a complex problem that often requires multiple physical or chemical analyses. In this study, LIBS and ATR-FTIR were used as fast and non-invasive methods to classify... more
Abstract The identification of counterfeit pharmaceutical packaging is a complex problem that often requires multiple physical or chemical analyses. In this study, LIBS and ATR-FTIR were used as fast and non-invasive methods to classify pharmaceutical paperboard packaging sample into an authentic group or belonging to one of five counterfeit counterpart packaging sources. The collection set consisted of 124 external pharmaceutical packages, originating from 6 authentic sources (n = 12 packages) and 3 to 5 counterfeit sources per product (n = 112 packages). Orthogonal methods, such as LIBS and ATR-FTIR, were especially advantageous for classification purposes because they reveal chemical information of the organic and inorganic components of the package ink. Different ink colors from the logo, text, barcodes, and images were tested; additionally, the paperboard sample substrate was analyzed with ATR-FTIR. After data reduction via Principal Component Analysis, two supervised machine learning classification techniques were used for classification: k-Nearest Neighbors, and Linear Discriminant Analysis. A random 60:40 split of the data was used for training and testing the algorithms. Across all analyzed ink types, correct classification rates above 70% (LIBS) and 85% (ATR-FTIR) were observed. Data fusion of the two complementary methods improved the results, providing correct classifications ranging from 90 to 100% depending on the classifier and the pharmaceutical package. The results demonstrate that the elemental information obtained by LIBS and the chemical composition by ATR-FTIR are complementary and provide practical alternatives for fast screening of counterfeit secondary packaging.
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Abstract This study evaluated the use of Laser Induced Breakdown Spectroscopy (LIBS) as a fast spectrochemical detection method for gunshot residues analysis around bullet orifices in complex substrates. Two approaches were assessed; the... more
Abstract This study evaluated the use of Laser Induced Breakdown Spectroscopy (LIBS) as a fast spectrochemical detection method for gunshot residues analysis around bullet orifices in complex substrates. Two approaches were assessed; the first one was aimed at shooting distance determination on bloody fabrics and the second one provided a fast bullet hole chemical identification. Fifty cotton-based clothing samples were fired from different distance intervals, with a 9 mm pistol, and then covered in human blood. Thirty of the clothing items were used as calibration samples and twenty samples were shot at distances unknown to the analysts and used as blind tests. LIBS ablations were used to developed elemental maps of the analytes present on each blood-stained sample. Following data acquisition, discriminant analysis was performed as a prediction tool for unknown distance samples. The LIBS method demonstrated superior performance when compared to physical examinations and color testing (100%, 50%, and 40% correct classification rates, respectively). Additionally, twenty-one glass, wood, and drywall substrates were shot from closed range and these materials were chemically mapped, using an optimized LIBS protocol. The substrates were specifically chosen to represent typical surface found at crime scenes that have shown challenging identification issues following traditional methods for bullet hole testing. The proposed method, presented in this project, allowed easy transfer of gunshot residues (GSR) from the substrates and quick mapping of GSR markers around the bullet orifice. LIBS offered improved analysis over conventional methods by eliminating the need of chemical reagents for testing, limiting sample preparation, enhancing selectivity, and generating permanent spectrochemical heat maps, and more accurate estimations for shooting distance determination and bullet hole identification.
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Information about the transfer and persistence of glass, as well as the frequency of occurrence of background glass in the general population, is key for the forensic interpretation of glass evidence. In this study, a mock case was... more
Information about the transfer and persistence of glass, as well as the frequency of occurrence of background glass in the general population, is key for the forensic interpretation of glass evidence. In this study, a mock case was designed to evaluate how glass shards are transferred during the breaking of a vehicle side (tempered) window, to what extent they persist through numerous activities, and to what extent they are prone to secondary transfer. Prior to the breaking, background glass was collected from those participating to provide a baseline control. A kidnapping scenario was devised and consisted of the breaking of a driver’s side car window with the victim in the driver’s seat and two suspects positioned around the breaking window. Following the smashing of the window, the victim was bound and thrown into the trunk of the suspects’ vehicle and then the suspects drove away. After the scenario concluded, evidence was collected from the victim, the suspects, the exterior of...
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This work investigated the prevalence of organic and inorganic gunshot residue within two main subpopulations, 1) non-shooters, including groups with low- and high-risk of potentially containing GSR-like residues, and 2) individuals... more
This work investigated the prevalence of organic and inorganic gunshot residue within two main subpopulations, 1) non-shooters, including groups with low- and high-risk of potentially containing GSR-like residues, and 2) individuals involved in a firing event (shooters, bystanders, and shooters performing post-shooting activities). The study analyzed over 400 samples via a liquid chromatography-mass spectrometry (LC-MS/MS) methodology with complexing agents. Exploratory statistical tools and machine learning algorithms (neural networks, NN) were used to evaluate the resulting mass spectral and quantitative data. This study observed lower occurrences of OGSR compounds in the non-shooter populations compared to IGSR analytes. The presence of GSR on authentic shooters versus other potential sources of false positives, such as bystanders and professions including police officers, agricultural workers, and mechanics, were further assessed by utilizing machine learning algorithms trained with the observed OGSR/IGSR traces. The probability of false negatives was also estimated with groups who performed regular activities after firing. Additionally, the low-risk background set allowed documentation of GSR occurrence in the general population. The probabilistic outputs of the neural network models were utilized to calculate likelihood ratios (LR) to measure the weight of the evidence. Using both the IGSR and OGSR profiles, the NN model’s accuracy ranged from 90 to 99%, depending on the subpopulation complexity. The log-LR histograms and Tippet plots show the method can discriminate between each sub-population and low rates of misleading evidence, suggesting that the proposed approach can be effectively used for a probabilistic interpretation of GSR evidence.
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Abstract Consensus concentration values for seventeen (17) major and trace elements typically present in soda-lime glass manufactured using the “float” process and used in the quantitative analysis and forensic comparison of glass samples... more
Abstract Consensus concentration values for seventeen (17) major and trace elements typically present in soda-lime glass manufactured using the “float” process and used in the quantitative analysis and forensic comparison of glass samples were determined using laser ablation (LA) micro sampling coupled to inductively coupled plasma mass spectrometry (ICP-MS). This is the first reporting of the chemical characterization of a new set of float glass intended for use as matrix-matched calibration standards in the forensic analysis and comparison of glass by LA-ICP-MS using a standard test method (ASTM E2927-16e1). Three Corning Float Glass Standards (CFGS) were manufactured at low, medium, and high concentrations of 32 elements typically encountered in float glass samples as found in forensic casework. This work describes an international collaboration among seven (7) laboratories to evaluate the homogeneity of the three glass materials and reports the consensus concentrations values of 17 elements at three concentration levels. Eight (8) sets of independent results from LA-ICP-MS analysis using the standard test method of analysis and one set of micro-X-ray Fluorescence Spectrometry (μXRF) data (using method ASTM E2926-17) resulted in typically
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Research Interests: Chemistry, Analytical Chemistry, Forensic Science, Data Analysis, Mass Spectrometry, and 15 moreGlass, Comparative Study, Medicine, Elemental analysis, Digestion, Laser Ablation, Chemical Analysis, Dissolution, Accuracy, Analytical Method, Analysis of Variance, Precision, Area of Interest, Elemental composition, and limit of detection
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ABSTRACT Four interlaboratory tests were designed to evaluate the performance of match criteria for forensic comparisons of elemental composition of glass by μ-XRF, solution nebulization SN-ICP-MS, LA-ICP-OES and LA-ICP-MS. A total of 24... more
ABSTRACT Four interlaboratory tests were designed to evaluate the performance of match criteria for forensic comparisons of elemental composition of glass by μ-XRF, solution nebulization SN-ICP-MS, LA-ICP-OES and LA-ICP-MS. A total of 24 analysts in 18 laboratories participated in the tests. Glass specimens were selected to study the capabilities of the techniques to discriminate glass produced in the same manufacturing plant at different time intervals and to associate samples that originated from a single source. The assessment of the effectiveness of several match criteria included: confidence interval (±6s, ±5s, ±4s, ±3s, ±2s), modified confidence interval, t-test, range overlap, and Hotelling's T2. Error rates are reported for each of these criteria. Recommended match criteria were those found to produce the lowest combinations of type 1 and type 2 error rates. Performance of the studied match criteria was dependent on the homogeneity of the glass sources, the repeatability between analytical measurements, and the number of elements that were measured. The best results for μ-XRF data were obtained using spectral overlay followed by a ±3s confidence interval or range overlap. For ICP-based measurements, a wider match criterion, such as a modified confidence interval based on a fixed minimum relative standard deviation (±4s, >3–5% RSD), is recommended due to the inherent precision of those methods (typically <1–5% RSD) and the greater number of elements measured. Glass samples that were manufactured in different plants, or at the same plant weeks or months apart, were readily differentiated by elemental composition when analyzed by these sensitive methods.
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This article describes the applicability of a rapid laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method for the analysis of soil and sediment samples with broad chemical and physical properties and the... more
This article describes the applicability of a rapid laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method for the analysis of soil and sediment samples with broad chemical and physical properties and the comparison of its analytical performance ...
Research Interests: Environmental Science, Multidisciplinary, Elemental analysis, Environmental Forensics, Heavy Metal, and 12 moreSediments, Soils, Laser Ablation, Inductively Coupled Plasma Mass Spectrometry, Contaminated soil, Natural Environment, Optical Emission Spectroscopy, Environmental, Physical Properties, Standard Reference Materials, Relative Standard Deviation, and Confidence Level
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The discrimination potential of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is compared with previously reported solution ICP-MS methods using external calibration (EC) with internal standardization and a newly... more
The discrimination potential of Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is compared with previously reported solution ICP-MS methods using external calibration (EC) with internal standardization and a newly reported solution isotope dilution (ID) method for the analysis of two different glass populations. A total of 91 different glass samples were used for the comparison study; refractive index and elemental composition were measured by the techniques mentioned above. One set consisted of 45 headlamps taken from a variety of automobiles that represents a range of 20 years of manufacturing dates. A second set consisted of 46 automotive glasses (side windows, rear windows, and windshields) representing casework glass from different vehicle manufacturers over several years. The element menu for the LA-ICP-MS and EC-ICP-MS methods include Mg, Al, Ca, Mn, Ce, Ti, Zr, Sb, Ga, Ba, Rb, Sm, Sr, Hf, La, and Pb. The ID method was limited to the analysis of two isotopes each of Mg, Sr, Zr, Sb, Ba, Sm, Hf, and Pb. Laser ablation analyses were performed with a Q switched Nd:YAG, 266 nm, 6 mJ output energy laser. The laser was used in depth profile mode while sampling using a 50 microm spot size for 50 sec at 10 Hz (500 shots). The typical bias for the analysis of NIST 612 by LA-ICP-MS was less than 5% in all cases and typically better than 5% for most isotopes. The precision for the vast majority of the element menu was determined generally less than 10% for all the methods when NIST 612 was measured (40 microg x g(-1)). Method detection limits (MDL) for the EC and LA-ICP-MS methods were similar and generally reported as less than 1 microg x g(-1) for the analysis of NIST 612. While the solution sample introduction methods using EC and ID presented excellent sensitivity and precision, these methods have the disadvantages of destroying the sample, and also involve complex sample preparation. The laser ablation method was simpler, faster, and produced comparable discrimination to the EC-ICP-MS and ID-ICP-MS. LA-ICP-MS can offer an excellent alternative to solution analysis of glass in forensic casework samples.
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Elemental analysis of glass was conducted by 16 forensic science laboratories, providing a direct comparison between three analytical methods [micro-x-ray fluorescence spectroscopy (μ-XRF), solution analysis using inductively coupled... more
Elemental analysis of glass was conducted by 16 forensic science laboratories, providing a direct comparison between three analytical methods [micro-x-ray fluorescence spectroscopy (μ-XRF), solution analysis using inductively coupled plasma mass spectrometry (ICP-MS), and laser ablation inductively coupled plasma mass spectrometry]. Interlaboratory studies using glass standard reference materials and other glass samples were designed to (a) evaluate the analytical performance between different laboratories using the same method, (b) evaluate the analytical performance of the different methods, (c) evaluate the capabilities of the methods to correctly associate glass that originated from the same source and to correctly discriminate glass samples that do not share the same source, and (d) standardize the methods of analysis and interpretation of results. Reference materials NIST 612, NIST 1831, FGS 1, and FGS 2 were employed to cross-validate these sensitive techniques and to optimize and standardize the analytical protocols. The resulting figures of merit for the ICP-MS methods include repeatability better than 5% RSD, reproducibility between laboratories better than 10% RSD, bias better than 10%, and limits of detection between 0.03 and 9 μg g(-1) for the majority of the elements monitored. The figures of merit for the μ-XRF methods include repeatability better than 11% RSD, reproducibility between laboratories after normalization of the data better than 16% RSD, and limits of detection between 5.8 and 7,400 μg g(-1). The results from this study also compare the analytical performance of different forensic science laboratories conducting elemental analysis of glass evidence fragments using the three analytical methods.
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Research Interests: Geology, Chemistry, Analytical Chemistry, Light Scattering, Environmental Chemistry, and 15 moreFood Chemistry, Instrumentation, Feasibility Study, Copper, Calibration, Data acquisition, Heavy Metal, Laser Ablation, Chemical Analysis, Atomic Absorption Spectrometry, Environmental Analysis, Inductively Coupled Plasma Mass Spectrometry, Ablation, Chemical Properties, and Figure of Merit
Laser ablation (LA) is a powerful analytical technique for solid microsampling. Its coupling with ICPMS has been shown to offer good precision and accuracy for the elemental analysis of glass fragments. Fractionation in LA poses one of... more
Laser ablation (LA) is a powerful analytical technique for solid microsampling. Its coupling with ICPMS has been shown to offer good precision and accuracy for the elemental analysis of glass fragments. Fractionation in LA poses one of the major challenges to using this technique for in situ trace elemental profiling of glass evidence. The aim of this work was to study the effect of elemental fractionation on the forensic application of elemental analysis of glass samples by LA-ICPMS. Two different approaches were used to evaluate the fractionation: fractionation index and U/Th ratios. The resulting fractionation index values indicate low fractionation for the majority of elements evaluated, ranging between 0.8 and 1.2. The U/Th ratio suggests a higher fractionation at the beginning of the ablation process. To evaluate whether fractionation affects the quantification of glass samples by LA-ICPMS, a comparison of LA results with solution ICPMS analysis was conducted. The distribution of particle sizes during the ablation under different conditions and laser systems was also measured to evaluate the fractionation. The standard reference materials NIST 612, 610, and 1831 were analyzed in triplicate by both methods (n = 55) along with a set of 10 casework samples originating from different automobiles.
Research Interests: Chemical Engineering, Chemistry, Analytical Chemistry, Forensic Science, Mass Spectrometry, and 11 moreGlass, Medicine, Quantitative analysis, Laser Ablation, Accuracy, Inductively Coupled Plasma Mass Spectrometry, Particle Size, Fractionation, Precision, Quantitative Analysis, and Certified Reference Material
The elemental analysis of glass samples for forensic use has been an interest in our group at Florida International University for over eight years as glass evidence can provide a way of associating a suspect to a crime. Laser ablation... more
The elemental analysis of glass samples for forensic use has been an interest in our group at Florida International University for over eight years as glass evidence can provide a way of associating a suspect to a crime. Laser ablation has been incorporated in our analytical scheme due to the many advantages that solid sampling holds over digestion of the glass followed by solution analysis using ICP-MS. The optimized conditions developed in our laboratory and by others are presented here for a specific combination of laser ablation system and ICP-MS instrument. The expected instrument responses for specific analytical conditions are presented. The method recommends using 29 Si as an internal standard, employing single spot ablation modes at a spot size of -50 μm and collecting -60 seconds of signal. Helium is used as a scavenging gas and a matrix-matched solid standard is recommended for quantification purposes. The procedure described should permit anyone with the described instru...
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This study reports novel approaches for the detection of gunshot residues (GSR) from the hands of individuals using Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS).... more
This study reports novel approaches for the detection of gunshot residues (GSR) from the hands of individuals using Laser-Induced Breakdown Spectroscopy (LIBS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS). The methods' performance was evaluated using 159 GSR standard and authentic samples. Forty specimens generated from characterized microparticles were used as matrix-matched primer gunshot residue (pGSR) standards to examine the elemental profiles of leaded and lead-free residues, compared to SEM-EDS and solution-ICP-MS. Also, 119 authentic skin samples were analyzed to estimate error rates. Shooter samples were correctly classified into three categories based on their elemental composition (leaded, lead-free, or mixed pGSR). A total of 60 non-shooter samples were used to establish background thresholds and estimate specificity (93.4% for LA-ICP-MS and 100% for LIBS). All the authentic leaded items resulted in the detection of particle(s) with com...
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LC-MS/MS and guest-host chemistry is a viable approach for the dual detection of organic and inorganic gunshot residue.