GSR2005—Continuity of the ENFSI Proficiency Test on Identification of GSR by SEM/EDX

Abstract:  Within the framework of the ENFSI Expert Working Group "Firearms" a proficiency test on the detection and identification of GSR by energy-dispersive scanning electron microanalysis (SEM/EDX) is carried out in a 2 years term. The latest test was performed in 2005/2006 and was denoted as GSR2005 . Seventy-five laboratories from 28 countries participated in this proficiency test and submitted in total 83 independent data-sets. The participating laboratories were requested to determine the total number of PbSbBa containing particles on a synthetic test sample following their own laboratory specific methods of automated GSR particle search and detection by SEM/EDX. Furthermore size and position of the detected particles had to be reported by the laboratories and were evaluated statistically. The results were compiled by means of z -scores according to the IUPAC and EURACHEM guidelines—assessing individual laboratory achievements (inter-laboratory) as well as intra-laboratory performance—and were compared to the results of the previous proficiency test run GSR2003 ( 1 ). The comparison shows that there is a noticeable improvement in the method's detection capability.     

Maintenance of the ENFSI proficiency test program on identification of GSR by SEM/EDX (GSR2003)

Within the framework of the ENFSI Expert Working Group "Firearms," every second year, a proficiency test on the detection and identification of GSR by SEM/EDX is carried out. This proficiency test is a development and extension of the previous proficiency test GSR2001. The test material was again designed by the organization panel and manufactured by an external company for SEM accessories. This time the participating laboratories were requested to determine the total number of PbSbBa containing particles on a test sample following their own laboratory specific methods of automated GSR particle search and detection by SEM/EDX. One synthetic particle sample (SPS) with artificial GSR particles was dispatched to all participants. This paper summarizes the results of the study and assesses the overall performance of the participating laboratories. Furthermore an extended statistical evaluation and a comparison with previous studies was carried out.     

GSR2005--continuity of the ENFSI proficiency test on identification of GSR by SEM/EDX.

Within the framework of the ENFSI Expert Working Group "Firearms" a proficiency test on the detection and identification of GSR by energy-dispersive scanning electron microanalysis (SEM/EDX) is carried out in a 2 years term. The latest test was performed in 2005/2006 and was denoted as GSR2005. Seventy-five laboratories from 28 countries participated in this proficiency test and submitted in total 83 independent data-sets. The participating laboratories were requested to determine the total number of PbSbBa containing particles on a synthetic test sample following their own laboratory specific methods of automated GSR particle search and detection by SEM/EDX. Furthermore size and position of the detected particles had to be reported by the laboratories and were evaluated statistically. The results were compiled by means of z-scores according to the IUPAC and EURACHEM guidelines-assessing individual laboratory achievements (inter-laboratory) as well as intra-laboratory performance-and were compared to the results of the previous proficiency test run GSR2003 (1). The comparison shows that there is a noticeable improvement in the method's detection capability.     

ENFSI proficiency test program on identification of GSR by SEM/EDX

Within the framework of the ENFSI Expert Working Group "Firearms," a proficiency test on the detection and identification of GSR by SEM/EDX was organized and performed. The test material was designed by the Bundeskriminalamt and manufactured to order by an external company for SEM accessories. The participating laboratories were requested to determine the total number of PbSbBa-containing particles on the test samples following their own laboratory specific methods of automated GSR particle search and detection by SEM/EDX. Two similar samples with synthetic GSR particles were dispatched to all participants in order to gain additional information on systematic errors within the obtained results (split-level study), whereas one sample was supplied only with PbSbBa particles, and the second one was additionally contaminated with some environmental particles. This report summarizes the results of the study as well as a statistical evaluation and comparison with previous studies.     

A New Method for the Removal and Analysis of Small Particles Adhering to Carpet Fiber Surfaces,,

Fibers are a commonly encountered evidence type and fiber comparisons are routinely conducted. When the characteristics of questioned and known fibers correspond, the probative value is limited because the characteristics compared are determined by their manufacture. It would be valuable to test the hypothesis that questioned fibers originated from a specific carpet. One means of testing this is to analyze fine particles on the fibers. A procedure was developed for removing adhering particles from fibers and preparing them for scanning electron microscopy/ energy dispersive X‐ray spectrometry (SEM/EDS) analysis. The efficacy of several fluids (acetone, ethanol, hexanes, aqueous ethanol, aqueous sodium hexametaphosphate) and agitation methods (sonication and vortexing) for removing particles from fibers was evaluated. The most effective method evaluated was sonication in ethanol for 10 min. The recovered particles were filtered onto a polycarbonate filter and analyzed by automated SEM/EDS analysis to generate data on the particle assemblage. This method makes possible future research to test the within‐item and between‐item variability of particle assemblages on fibers.     

A novel platform for the modular integration of forensic assay setup and medium- to high-throughput purification of nucleic acids

With its extraction and assay setup modules, the QIAsymphony^® provides a highly flexible solution for processing forensic samples in a medium- to high-throughput scale. We tested the sensitivity of extraction, precision of sample processing, and accuracy of automated assay setup of this integrated system. Results attest to QIAsymphony's ability to isolate DNA from a spectrum of common forensic samples and process these samples without cross-contamination. Furthermore, accurate assay setup for downstream applications, like PCR, make this system highly suited for enhancing laboratory workflow.     

Locating,Identifying, and Comparing Sub‐visible Paint Particles

Forensic paint comparisons are generally conducted on samples which, while small relative to their source, are still visible to the unaided eye and are thus located and analyzed without great difficulty. Here we demonstrate that a more detailed examination of candidate transfer surfaces can capture materials (questioned samples), even when such traces are invisible to the unaided eye. While certain analytical details (such as layer sequence or a pure FTIR spectrum) may not be obtainable from such traces due to their size and condition, a detailed analysis of the sample characteristics that are analytically accessible may still provide sufficient analytical data to arrive at a probative result. Here we present the application of this approach to a suspected paint transfer case, involving particles of paint as small as 40 μm in size. Using a combination of stereomicroscopy, polarized light microscopy, infrared microspectroscopy, Raman microspectroscopy, and SEM/EDS, all performed on a single, subsample of the original minute particle, it was possible to demonstrate evidence of a two‐way transfer between the suspected sources. Furthermore, the transferred paint particle in one direction could be classified as automotive in nature based on a combination of polymer composition, microscopic texture, and pigment package (which included three specifically identified pigments). This work demonstrates (i) the potential for improving detection limits when searching for a questioned sample, (ii) the potential benefits of higher resolution analyses on samples that would be traditionally labeled as “sample‐size limited,” and (iii) the value of case‐specific interpretation over standardized, one‐size fits all report templates.     

Automated Mapping of Explosives Particles in Composition C‐4 Fingerprints*†‡

Abstract: A method is described to perform automated mapping of hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) particles in C‐4 fingerprints. The method employs polarized light microscopy and image analysis to map the entire fingerprint and the distribution of RDX particles. This method can be used to evaluate a large number of fingerprints to aid in the development of threat libraries that can be used to determine performance requirements of explosive trace detectors. A series of 50 C‐4 fingerprints were characterized, and results show that the number of particles varies significantly from print to print, and within a print. The particle size distributions can be used to estimate the mass of RDX in the fingerprint. These estimates were found to be within ±26% relative of the results obtained from dissolution gas chromatography/μ‐electron capture detection for four of six prints, which is quite encouraging for a particle counting approach. By evaluating the average mass and frequency of particles with respect to size for this series of fingerprints, we conclude that particles 10–20 μm in diameter could be targeted to improve detection of traces of C‐4 explosives.     

Preparation of a Ytterbium‐tagged Gunshot Residue Standard for Quality Control in the Forensic Analysis of GSR

Preparation of a ytterbium‐tagged gunshot residue (GSR) reference standard for scanning electron microscopy and energy dispersive X‐ray spectroscopic (SEM‐EDS) microanalysis is reported. Two different chemical markers, ytterbium and neodymium, were evaluated by spiking the primers of 38 Special ammunition cartridges (no propellant, no projectile) and discharging them onto 12.7 mm diameter aluminum SEM pin stubs. Following SEM‐EDS microanalysis, the majority of tri‐component particles containing lead, barium, and antimony (PbBaSb) were successfully tagged with the chemical marker. Results demonstrate a primer spiked with 0.75% weight percent of ytterbium nitrate affords PbBaSb particles characteristic of GSR with a ytterbium inclusion efficiency of between 77% and 100%. Reproducibility of the method was verified, and durability of the ytterbium‐tagged tri‐component particles under repeated SEM‐EDS analysis was also tested. The ytterbium‐tagged PbBaSb particles impart synthetic traceability to a GSR reference standard and are suitable for analysis alongside case work samples, as a positive control for quality assurance purposes.     

The Effect of Skin Debris on Gunshot Residue Sampling and Detection

These experiments were designed to determine whether skin debris (desquamated epithelial cells and apparent skin oils) affects gunshot residue (GSR) particle detection on the sticky tape lift samples prepared for scanning electron microscopy (SEM). A dabbing experiment showed that GSR particles accumulate not only on the adhesive surface of the sampler, but also on the epithelial cell surfaces. Samplers were loaded with target GSR followed by dabbing 30 times on the back of a hand. Backscatter electron images were taken at 20 kV and for some at 30 kV of the same areas. The samplers were then treated with a sodium/calcium hypochlorite solution (bleach) to remove skin debris and again imaged in the SEM. Comparison of these images shows more GSR particles will likely be revealed at 30 kV than 20 kV and more particles revealed by the bleach treatment in an automated SEM system.     

Forensic Comparison of Automotive Aluminum Wheel Fragments Using Synchrotron Radiation X‐ray Fluorescence with 18‐ and 116‐keV Excitation X‐rays

The performance of synchrotron radiation X‐ray fluorescence (SR‐XRF) spectrometry for nondestructive discrimination of small fragments of automotive aluminum wheels was studied. Fragments (< 500 × 500 μm²) of 45 kinds of wheels were first analyzed by scanning electron microscopy–energy dispersive spectroscopy (SEM‐EDS) and then by SR‐XRF. Despite the Mg/Al intensity ratio being a useful identification index, SEM‐EDS was not efficient enough because of the absence of other meaningful indicators of comparison. Conversely, pairwise comparison was conducted and a 92.9% identification was achieved via SR‐XRF using 18‐keV X‐rays. Trace heavy elements in the high‐energy region were detected by SR‐XRF using 116‐keV X‐rays, and an 82.9% identification was obtained. Combined use of 18‐ and 116‐keV X‐rays allowed 98.2% identification. Hence, SR‐XRF is a powerful tool for nondestructive discrimination of automotive aluminum wheels with high precision using trace elements in a wide energy region.     

Validation of a DNA Quantitation Method on the Biomek® 3000

Abstract: Laboratory automation has the ability to increase the throughput and efficiency of laboratory processes to keep pace with current backlogs and requests for analysis. This paper addresses the specific studies employed to properly evaluate an automated method for DNA quantitation setup using Applied Biosystems Quantifiler? Human DNA Quantification kit on a Biomek^® 3000. The calibration of robotic pipetting as well as comparison with manually performed steps confirmed the accuracy of the automated methods used. Reproducibility studies evaluated differences between robotic and manually prepared human DNA standard curves. Additional studies examined DNA samples of known quantities, extract storage formats, sensitivity, and an assessment of contamination. The Biomek^® 3000 not only demonstrated reproducibility and accuracy that equaled or surpassed the manual method but also revealed a contamination‐free method to replace the multiple pipetting steps required during quantitation setup.     

Particle size distribution analysis of soils using laser diffraction

The use of laser diffraction for the particle size distribution analysis of the sub-63 μm fraction of soil samples is described. Each sub-63 μm fraction was obtained from the wet sieving of 1500 mg of whole soil. Using similarity probabilities, the data obtained, when combined with other information from wet sieving and/or organic matter content, will enable the correct identity of a given soil sample with that of an unknown to be made. Although the sub-63 μm fraction can account for 450 mg or more of the total soil content, analyses of this fraction can be conducted on sample sizes as small as 100 mg.     

扫描电子显微镜/能谱法对铊盐的检验

目的建立投毒案件中铊元素的一种快速定性检验方法。方法：在扫描电子显微镜下用背散射电子探头（BSE）观察处理后的样品,观察图像中根据元素衬度差异挑选出可能含铊元素的区域,用能谱仪做该区域的元素定性检验。结果能谱分析仪可以很快对各种元素做出准确的定性检验。结论扫描电子显微镜/能谱法对疑似铊中毒案的检验快速、灵敏、准确。     

Characterization and differentiation of aluminum powders used in improvised explosive devices – Part 1: Proof of concept of the utility of particle micromorphometry

Aluminum (Al) powders are commonly used in improvised explosive devices as metallic fuels, a component of explosive mixtures. These powders can be obtained readily from industrial‐scale and consumer products, and produced using unsophisticated “kitchen chemistry” techniques. This research demonstrates the potential of automated particle micromorphometry for comparisons between known source and questioned Al powders recovered from IEDs, as well as for insight into the method of Al powder manufacture. Al powder samples were obtained from legitimate manufacturers, and 56 samples were produced “in‐house” from Al‐containing spray paints and ball‐milled Al foils. Transmitted light microscope images of Al powder particles were acquired using an automated stage with automated z‐focus; 17 size and shape parameters were measured for all particles. Approximately 37,000–2,500,000 particles/sample were analyzed using an open‐source statistical package with customized code. Dimensionality reduction was required for processing the large datasets: eight of the 17 measured variables were selected based on inspection of the correlation matrix. Data from four subsamples from each of the 56 samples produced using “in‐house” methods were analyzed using ANOVA to assess the within‐ and between‐sample variation. High within‐sample variation was noted; however, ANOVA and post‐hoc Tukey's honestly significant difference (HSD) tests demonstrated that the between‐sample variation was substantially larger than the within‐sample variation. Each sample could be differentiated from all other samples in the test set. Future experiments will focus on ways to reduce the within‐sample variation, and additional statistical and microanalytical methods to classify sources and confidently constrain the method of Al powder manufacture.     

扫描电镜/X射线能谱仪检验电流斑规范化方法探讨

目的探讨电流斑皮肤金属化的机理、检材提取处理和扫描电镜/能谱仪检验规范化方法,对检验结果进行分析和价值判断。方法用扫描电镜/能谱检验,采用低倍大窗口覆盖损伤区域采集平均元素能谱图,并在可能的金属元素富集区域寻找球形金属颗粒。结果扫描电镜下可观察到散在的孔穴、细胞碎屑、龟裂、裂隙等特征,有些电流斑可检出金属元素,其中部分电流斑可发现球形金属颗粒。结论采用规范化的检材提取、处理和检验方法可消除随意性方法造成错检的可能。电流斑皮肤上异常含量的金属附着可支持病理检验符合电流斑表现的结论,同时也为电击导体的推断和金属元素成分比对提供依据。球形金属颗粒的发现揭示存在电弧高温的可能性极大,可强力支持病理检验符合电流斑表现的结论。     

Characterization of pyrotechnic reaction residue particles by SEM/EDS

Today the method commonly used for detecting gunshot residue is through the combined use of scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). In recent years, this same methodology began to find use in detecting and characterizing pyrotechnic reaction residue (PRR) particles whether produced by explosion or burning. This is accomplished by collecting particulate samples from a surface in the immediate area of the pyrotechnic reaction. Suspect PRR particles are identified by their morphology (typically 1 to 20 microm spheroidal particles) using an SEM; then they are analyzed for the elements they contain using X-ray EDS. This can help to identify the general type of pyrotechnic composition involved.     

Automated Quantifiler quantitative PCR setup, template normalization and PCR setup using HID EVOlution™ qPCR/STR setup on trace evidence samples

We have implemented and validated customized protocols for automated Quantifiler^® setup, template normalization and PCR setup using the Tecan HID EVOlution™ qPCR/STR setup. The protocols were validated for the Quantifiler^® human DNA quantification, AmpF?STR^® SGM Plus^® and SEfiler Plus™ PCR Amplification Kits (Applied Biosystems) according to EN/ISO 17025.     

Particle characteristics of trace high explosives: RDX and PETN

The sizes of explosives particles in fingerprint residues produced from C-4 and Semtex-1A were investigated with respect to a fragmentation model. Particles produced by crushing crystals of RDX and PETN were sized by using scanning electron microscopy, combined with image analysis, and polarized light microscopy was used for imaging and identifying explosive particles in fingerprint residues. Crystals of RDX and PETN fragment in a manner that concentrates mass in the largest particles of the population, which is common for a fragmentation process. Based on the fingerprints studied, the particle size to target for improving mass detection in fingerprint residues by ion mobility spectrometry (IMS) is > or = 10 microm in diameter. Although particles smaller than 10 microm in diameter have a higher frequency, they constitute < 20% of the total mass. Efforts to improve collection efficiency of explosives particles for detection by IMS, or other techniques, must take into consideration that the mass may be concentrated in a relatively few particles that may not be homogeneously distributed over the fingerprint area. These results are based on plastic-bonded explosives such as C-4 that contain relatively large crystals of explosive, where fragmentation is the main process leading to the presence of particles in the fingerprint residues.     

Handguns and ammunitions indicators extracted from the GSR analysis

The computer automated scanning electron microscope. X-ray microanalysis of Firearms Discharge Residue (FDR) can reveal substantial information about the circumstances of their generation beyond the presence of characteristic gunshot residue (GSR). Indicators of the type of weapon and ammunition used can he obtained from the distribution of GSR particle shapes and from the multi-element analysis of the FDR sample. This is demonstrated for a large database of GSR samples from nine different handguns and over 60 different ammunitions. An example classification scheme is presented for the supporting particles generally found present in FDR. When particle type area concentration ratios are normalized to the iron (Fe) particle type, results show it is possible to distinguish much about the metal used in the weapon manufacture, whether it was of large or small caliber, whether the bullets were jacketed or plated, and whether the cartridge cases were of aluminum, brass, or nickel-plated brass. Standardization of such analytical schemes would be advantageous.