Heroin manufacturing and distribution by criminal and terrorist organizations produce illicit economic benefits from the opium and heroin trade and result in devastating societal problems. Heroin chemical signatures provide important information to law enforcement and the intelligence community in order to combat the national and international heroin epidemic. Authentic (known origin) heroin samples from Southeast Asia (SEA), Southwest Asia (SWA), South America (SA) and SA-like heroin manufactured in Mexico (MEX-SA), were prepared for chemical analysis by microwave-assisted acid digestion. Strontium concentration data were acquired using inductively-coupled plasma mass spectrometry (ICP-MS). The samples having sufficient [88Sr] (1.25 µg/g in the solid sample) were purified by ion exchange resin and strontium isotope ratio (87Sr/86Sr) values were measured using multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS).South American and MEX-SA heroin samples are presently the most challenging regions to differentiate by analysis of their organic compositions. The SA and MEX-SA heroin samples were correctly classified 82% and 77% of the time, respectively, when the 87Sr/86Sr values of individual authentic samples were compared to the overall mean values from the four regions. This is the first reporting on the use of 87Sr/86Sr analysis of heroin for the profiling of samples from specific geographic regions. In addition, a value of 87Sr/86Sr for the National Institute of Standards and Testing’s standard reference material NIST SRM 1570a (spinach leaves) of 0.70905 ± 0.00002 (95% confidence interval, n = 3) is also reported for the first time.Download high-res image (92KB)Download full-size image

•A novel LA-ICP-MS method was evaluated for the chemical characterization and comparison of electrical tape backings.•LA-ICP-MS provided improved discrimination (93.9%) when compared with SEM-EDS (87.3%).•LA-ICP-MS represents a quick, sensitive, and selective method for the elemental analysis of tape evidence.•The elemental menu for the analysis of tapes increased to 29 elements by using LA-ICP-MS.•The numerical nature of the data generated is amenable for the creation of a searchable database.Adhesive tapes are commonly found as physical evidence in cases involving violent crimes and national security threats. This research evaluated the utility of Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) for the characterization of chemical signatures of electrical tapes for forensic comparison and provenance purposes. The backings of 90 black electrical tapes, previously characterized by microscopical examination, Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FTIR) and Pyrolysis–Gas Chromatography–Mass Spectrometry (Py–GC–MS), were analyzed by LA-ICP-MS to evaluate the ability of the technique to discriminate samples originating from different sources and to associate pieces of tapes originating from the same roll. The results showed that LA-ICP-MS is a useful tool that complements current protocols for the organic and inorganic characterization and comparison of electrical tapes and results in improved discrimination and superior characterization. The developed LA-ICP-MS method alone provided 94% correct discrimination of the tapes known to originate from different rolls and 100% correct association of the tapes known to originate from the same roll. Moreover, LA-ICP-MS captured a large amount of compositional information, as the use of elemental profiles alone provide similar discrimination and classification capabilities as all the conventional methods together. The analytical sensitivity of LA-ICP-MS provides a means for the classification of tapes to support investigations as well as the potential for database searching capabilities in the future.Download high-res image (107KB)Download full-size image

•Capillary micro-extraction of volatiles was used for breath analysis of smokers and non-smokers.•CMV identified 108 compounds in the breath of with 12 compounds determined as significant.•PCA was used to elucidate the groupings and non-smokers were correctly classified 100% of the time.•Future applications of CMV include detection of marijuana smokers’ breath for impaired drivers.The aim of this research was to investigate the potential of a novel preconcentration device, capillary micro-extraction of volatiles (CMV), for the application of breath analysis. The CMV offers dynamic sampling of volatile to semi-volatile organic compounds (VOCs) by the simple coupling of an adapter to a GC inlet for GC/MS analysis, in comparison to the expensive thermal desorption units needed for sorbent tubes. It additionally offers an increased surface area over a single SPME fiber. The CMV was used to sample and extract 108 compounds from the breath of 11 self-reported cigarette smokers and 7 non-smokers. Twelve (12) compounds were determined to be statistically significant between the groups. Principal Component Analysis (PCA) and Linear Discriminant Analysis (LDA) were used to distinguish the groups, resulting in 100% correct classification of all non-smokers. In some cases, nicotine was not detected in smokers and therefore some of those smokers were confused with the non-smokers. Nicotine was detected in the breath of 64% of all cigarette smokers with an average mass of 143 ± 31 pg from the approximate 5-liter breath sample collected within 1 h after smoking. The successful use of the CMV sampler for preconcentration of breath to distinguish between smokers and non-smokers serves as a proof of concept for future applications of the CMV for detection of marijuana smokers’ breath for impaired driver management.Download high-res image (85KB)Download full-size image

•Fast detection and characterization of gunshot residues by LIBS and GC-MS•New application of capillary microextraction of volatiles (CMV) for detection of volatiles associated with GSR presence•Quantitation of inorganic and organic components present in GSR•Evaluation of residues found on the hands of shooters and non-shooters•The combination of both inorganic and organic analysis will allow better characterization and faster identification of GSRA rapid method for the characterization of both organic and inorganic components of gunshot residues (GSR) is proposed as an alternative tool to facilitate the identification of a suspected shooter. In this study, two fast screening methods were developed and optimized for the detection of organic compounds and inorganic components indicative of GSR presence on the hands of shooters and non-shooters. The proposed methods consist of headspace extraction of volatile organic compounds using a capillary microextraction of volatiles (CMV) device previously reported as a high-efficiency sampler followed by detection by GC–MS. This novel sampling technique has the potential to yield fast results (< 2 min sampling) and high sensitivity capable of detecting 3 ng of diphenylamine (DPA) and 8 ng of nitroglycerine (NG). Direct analysis of the headspace of over 50 swabs collected from the hands of suspected shooters (and non-shooters) provides information regarding VOCs present on their hands. In addition, a fast laser induced breakdown spectroscopy (LIBS) screening method for the detection of the inorganic components indicative of the presence of GSR (Sb, Pb and Ba) is described. The sampling method for the inorganics consists of liquid extraction of the target elements from the same cotton swabs (previously analyzed for VOCs) and an additional 30 swab samples followed by spiking 1 μL of the extract solution onto a Teflon disk and then analyzed by LIBS. Advantages of LIBS include fast analysis (~ 12 s per sample) and high selectivity and sensitivity, with expected LODs 0.1–18 ng for each of the target elements after sampling. The analytical performance of the LIBS method is also compared to previously reported methods (inductively coupled plasma–optical emission spectroscopy). The combination of fast CMV sampling, unambiguous organic compound identification with GC–MS and fast LIBS analysis provides the basis for a new comprehensive screening method for GSR.

•The optimization of the parameters for LA-ICP-MS and LIBS in a tandem experiment are presented.•The analytical figures of merit for the tandem experiment for data collected simultaneously, are presented.•A qualitative and semi-quantitative method for the analysis of toner, inkjet, offset and Intaglio inks is presented.•The LIBS and LA-ICP-MS data are shown to be complementary and can augment discrimination over a single technique.•Major, minor and trace elements present in ink samples can serve as good discriminators for a variety of printing inks.•LIBS was successful to overcome spectral interferences of ICP-MS for some discriminating elements like K, Ca, Si and Fe.•Fusion of LIBS and LA-ICP-MS has proven to provide complementary information and enhanced discrimination for printing inks.Elemental analysis, using either LA-ICP-MS or LIBS, can be used for the chemical characterization of materials of forensic interest to discriminate between source materials originating from different sources and also for the association of materials known to originate from the same source. In this study, a tandem LIBS/LA-ICP-MS system that combines the benefits of both LIBS and LA-ICP-MS was evaluated for the characterization of samples of printing inks (toners, inkjets, intaglio and offset.). The performance of both laser sampling methods is presented. A subset of 9 black laser toners, 10 colored (CMYK) inkjet samples, 12 colored (CMYK) offset samples and 12 intaglio inks originating from different manufacturing sources were analyzed to evaluate the discrimination capability of the tandem method. These samples were selected because they presented a very similar elemental profile by LA-ICP-MS. Although typical discrimination between different ink sources is found to be > 99% for a variety of inks when only LA-ICP-MS was used for the analysis, additional discrimination was achieved by combining the elemental results from the LIBS analysis to the LA-ICP-MS analysis in the tandem technique, enhancing the overall discrimination capability of the individual laser ablation methods. The LIBS measurements of the Ca, Fe, K and Si signals, in particular, improved the discrimination for this specific set of different ink samples previously shown to exhibit very similar LA-ICP-MS elemental profiles. The combination of these two techniques in a single setup resulted in better discrimination of the printing inks with two distinct fingerprint spectra, providing information from atomic/ionic emissions and isotopic composition (m/z) for each ink sample.

•We describe the analysis of printer inks on paper using LA-ICP-MS, LIBS and SEM-EDS.•Analytical figures of merit and the relative discrimination power for each technique is described.•Both LA-ICP-MS and LIBS provide excellent discrimination between different printer sources.Detection and sourcing of counterfeit currency, examination of counterfeit security documents and determination of authenticity of medical records are examples of common forensic document investigations. In these cases, the physical and chemical composition of the ink entries can provide important information for the assessment of the authenticity of the document or for making inferences about common source. Previous results reported by our group have demonstrated that elemental analysis, using either Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) or Laser Ablation Induced Breakdown Spectroscopy (LIBS), provides an effective, practical and robust technique for the discrimination of document substrates and writing inks with minimal damage to the document. In this study, laser-based methods and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDS) methods were developed, optimized and validated for the forensic analysis of more complex inks such as toners and inkjets, to determine if their elemental composition can differentiate documents printed from different sources and to associate documents that originated from the same printing source. Comparison of the performance of each of these methods is presented, including the analytical figures of merit, discrimination capability and error rates. Different calibration strategies resulting in semi-quantitative and qualitative analysis, comparison methods (match criteria) and data analysis and interpretation tools were also developed. A total of 27 black laser toners originating from different manufacturing sources and/or batches were examined to evaluate the discrimination capability of each method. The results suggest that SEM-EDS offers relatively poor discrimination capability for this set (~ 70.7% discrimination of all the possible comparison pairs or a 29.3% type II error rate). Nonetheless, SEM-EDS can still be used as a complementary method of analysis since it has the advantage of being non-destructive to the sample in addition to providing imaging capabilities to further characterize toner samples by their particle morphology. Laser sampling methods resulted in an improvement of the discrimination between different sources with LIBS producing 89% discrimination and LA-ICP-MS resulting in 100% discrimination. In addition, a set of 21 black inkjet samples was examined by each method. The results show that SEM-EDS is not appropriate for inkjet examinations since their elemental composition is typically below the detection capabilities with only sulfur detected in this set, providing only 47.4% discrimination between possible comparison pairs. Laser sampling methods were shown to provide discrimination greater than 94% for this same inkjet set with false exclusion and false inclusion rates lower than 4.1% and 5.7%, for LA-ICP-MS and LIBS respectively. Overall these results confirmed the utility of the examination of printed documents by laser-based micro-spectrochemical methods. SEM-EDS analysis of toners produced a limited utility for discrimination within sources but was not an effective tool for inkjet ink discrimination. Both LA-ICP-MS and LIBS can be used in forensic laboratories to chemically characterize inks on documents and to complement the information obtained by conventional methods and enhance their evidential value.

•An evaluation of LA-ICP-OES for the direct analysis of pelleted plant material is reported.•Orange citrus, soy and sugarcane plants were pressed into pellets and sampled directly.•The element menu consisted of Ca, Mg, P, K, Fe, Mn, Zn and B.•LODs for the method ranged from 0.1 mg kg− 1 for Zn to 94 mg kg− 1 for K.•The precision ranged from 4% RSD for Mn to 17% RSD for Zn (~ 6.5% RSD average).An evaluation of laser ablation inductively coupled plasma optical emission spectroscopy (LAICP OES) for the direct analysis of pelleted plant material is reported. Ground leaves of orange citrus, soy and sugarcane were comminuted using a high-speed ball mill, pressed into pellets and sampled directly with laser ablation and analyzed by ICP OES. The limits of detection (LODs) for the method ranged from as low as 0.1 mg kg− 1 for Zn to as high as 94 mg kg− 1 for K but were generally below 6 mg kg− 1 for most of the elements of interest. A certified reference material consisting of a similar matrix (NIST SRM 1547 peach leaves) was used to check the accuracy of the calibration and the reported method resulted in an average bias of ~ 5% for all the elements of interest. The precision for the reported method ranged from as low as 4% relative standard deviation (RSD) for Mn to as high as 17% RSD for Zn but averaged ~ 6.5% RSD for all the elements (n = 10). The proposed method was tested for the determination of Ca, Mg, P, K, Fe, Mn, Zn and B, and the results were in good agreement with those obtained for the corresponding acid digests by ICP-OES, no differences being observed by applying a paired t-test at the 95% confidence level. The reported direct solid sampling method provides a fast alternative to acid digestion that results in similar and appropriate analytical figures of merit with regard to sensitivity, accuracy and precision for plant material analysis.

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.

The present work highlights the effect that solvent chemistry has on analytes being detected when utilizing electrospray ionization in ion mobility mass spectrometers. Various studies were conducted involving both positive and negative mode ionization. The enhancements observed by utilizing different levels of acid modifiers as well as the different ionic species of analytes being formed and detected are presented. The makeup of the electrospray solvent determined whether the ionic species would be protonated, sodium adducted, ammonium adducted, proton abstracted or chlorinated. Addition of solvent modifiers such as acids in the positive mode, and organic halides in the negative mode improved signal strength of analytes as well as improved spray characteristics that also decreased signal variability. The ability to perform simultaneous ionization of complex mixtures was also demonstrated through the use of solvent modifiers thereby allowing electrospray ionization ion mobility mass spectrometry the ability to simultaneously analyze complicated mixtures very quickly (millisecond separations).

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.

Laser induced breakdown spectroscopy (LIBS) is shown to be capable of low volume (90 pL) quantitative elemental analysis of picogram amounts of dissolved metals in solutions. Single-pulse and collinear double-pulse LIBS were investigated using a 532 nm dual head laser coupled to a spectrometer with an intensified charge coupled device (CCD) detector. Aerosols were produced using a micronebulizer, conditioned inside a concentric spray chamber, and released through an injector tube with a diameter of 1 mm such that a LIBS plasma could be formed ∼2 mm from the exit of the tube. The emissions from both the aerosols and a single microdrop were then collected with a broadband high resolution spectrometer. Multielement calibration solutions were prepared, and continuing calibration verification (CCV) standards were analyzed for both aerosol and microdrop systems to calculate the precision, accuracy, and limits of detection for each system. The calibration curves produced correlation coefficients with R2 values > 0.99 for both systems. The precision, accuracy, and limit of detection (LOD) determined for aerosol LIBS were averaged and determined for the emission lines of Sr II (421.55 nm), Mg II (279.80 nm), Ba II (493.41 nm), and Ca II (396.84 nm) to be ∼3.8% RSD, 3.1% bias, 0.7 μg/mL, respectively. A microdrop dispenser was used to deliver single drops containing 90 pL into the space where a LIBS plasma was generated with a focused laser pulse. In the single drop microdrop LIBS experiment, the analysis of a single drop, containing a total mass of 45 pg, resulted in a precision of 13% RSD and a bias of 1% for the Al I (394.40 nm) emission line. The absolute limits of detection of single drop microdrop LIBS for the emission lines Al I (394.40 nm) and Sr II (421.5 nm) were approximately 1 pg, and Ba II (493.41 nm) produced an absolute detection limit of approximately 3 pg. Overall, the precision, accuracy, and absolute LOD determined for single microdrop LIBS resulted in a typical performance of ∼14% RSD, 6% bias, and 1 pg for the elements Sr II (421.55 nm), Al I(394.40 nm), Mg II (279.80), and Ba II(493.41 nm).

The elemental analysis of glass evidence has been established as a powerful discrimination tool for forensic analysts. Laser ablation inductively coupled plasma optical emission spectrometry (LA-ICP-OES) has been compared to laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and energy dispersive micro X-ray fluorescence spectroscopy (μXRF/EDS) as competing instrumentation for the elemental analysis of glass. The development of a method for the forensic analysis of glass coupling laser ablation to ICP-OES is presented for the first time. LA-ICP-OES has demonstrated comparable analytical performance to LA-ICP-MS based on the use of the element menu, Al (Al I 396.15 nm), Ba (Ba II 455.40 nm), Ca (Ca II 315.88 nm), Fe (Fe II 238.20 nm), Li (Li I 670.78 nm), Mg (Mg I 285.21 nm), Sr (Sr II 407.77 nm), Ti (Ti II 368.51 nm), and Zr (Zr II 343.82 nm). The relevant figures of merit, such as precision, accuracy and sensitivity, are presented and compared to LA-ICP-MS. A set of 41 glass samples was used to assess the discrimination power of the LA-ICP-OES method in comparison to other elemental analysis techniques. This sample set consisted of several vehicle glass samples that originated from the same source (inside and outside windshield panes) and several glass samples that originated from different vehicles. Different match criteria were used and compared to determine the potential for Type I and Type II errors. It was determined that broader match criteria is more applicable to the forensic comparison of glass analysis because it can reduce the affect that micro-heterogeneity inherent in the glass fragments and a less than ideal sampling strategy can have on the interpretation of the results. Based on the test set reported here, a plus or minus four standard deviation (±4 s) match criterion yielded the lowest possibility of Type I and Type II errors. The developed LA-ICP-OES method has been shown to perform similarly to LA-ICP-MS in the discrimination among different sources of glass while offering the advantages of a lower cost of acquisition and operation of analytical instrumentation making ICP-OES a possible alternative elemental analysis method for the forensic laboratory.

Triacetone triperoxide (TATP) is a high explosive synthesized from easily available reactants making it accessible for illicit uses. In this study, fast detection of TATP is achieved using a novel planar solid-phase microextraction (PSPME) as a preconcentration and sampling device for headspace analysis offering improved sensitivity and reduced sampling time over the conventional fiber-based solid-phase microextraction (SPME) when followed by ion mobility spectrometer (IMS) detection. Quantitation and comparison of the retention capabilities of PSPME as compared to the commercially available SPME were determined using TATP standards and analyzed using gas chromatography–mass spectrometry for SPME analysis and a commercial IMS with no instrumental modification for PSPME. Static and dynamic headspace extractions were used and compared for PSPME extractions, in which low milligram quantities of TATP were detected within 30 s of static mode sampling and less than 5 s in the dynamic mode sampling for PSPME–IMS.

Smokeless powder additives are usually detected from an extraction of post-blast residues or unburned powder particles followed by chromatographic analyses. This work presents the first comprehensive study of the detection of volatile and semi-volatile additives of smokeless powders using solid phase microextraction (SPME) as a sampling and pre-concentration technique. The goal of this study is to generate a list of compounds that can be used as target compounds for the vapor phase detection of smokeless powders. Sixty-five smokeless powders were studied using laboratory-based gas chromatography techniques and a field deployable ion mobility spectrometer (IMS). The detection of diphenylamine, ethyl and methyl centralite, 2,4-dinitrotoluene, diethyl and dibutyl phthalate by IMS is suggested as a method to indicate the presence of smokeless powders. A previously reported SPME–IMS analytical approach facilitates rapid sub-nanogram detection of the vapor phase components of smokeless powders. The analyte mass present in the vapor phase was sufficient for a SPME fiber to extract and concentrate most analytes at amounts above the detection limits of both the GC and the IMS methods. Analysis of 65 different smokeless powder samples revealed that diphenylamine was present in the headspace of 96% of the powders studied. Ethyl centralite was detected in 47% of the powders and 8% of the powders contained methyl centralite. Nitroglycerin was the dominant peak present in the headspace of the double-based powders. Another important headspace component, 2,4-dinitrotoluene, was detected in 44% of the powders comprising both double and single-based powders. Static headspace SPME of small amounts (∼100 mg) of smokeless powder samples for ∼5 min at room temperature resulted in the successful detection of the headspace components, demonstrating the applicability of the technique for field detection of smokeless powders using IMS as a detector.

A method for the quantitative elemental analysis of surface soil samples using laser-induced breakdown spectroscopy (LIBS) was developed and applied to the analysis of bulk soil samples for discrimination between specimens. The use of a 266 nm laser for LIBS analysis is reported for the first time in forensic soil analysis. Optimization of the LIBS method is discussed, and the results compared favorably to a laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) method previously developed. Precision for both methods was <10% for most elements. LIBS limits of detection were <33 ppm and bias <40% for most elements. In a proof of principle study, the LIBS method successfully discriminated samples from two different sites in Dade County, FL. Analysis of variance, Tukey’s post hoc test and Student’s t test resulted in 100% discrimination with no type I or type II errors. Principal components analysis (PCA) resulted in clear groupings of the two sites. A correct classification rate of 99.4% was obtained with linear discriminant analysis using leave-one-out validation. Similar results were obtained when the same samples were analyzed by LA-ICP-MS, showing that LIBS can provide similar information to LA-ICP-MS. In a forensic sampling/spatial heterogeneity study, the variation between sites, between sub-plots, between samples and within samples was examined on three similar Dade sites. The closer the sampling locations, the closer the grouping on a PCA plot and the higher the misclassification rate. These results underscore the importance of careful sampling for geographic site characterization.

A preconcentration device that targets the volatile chemical signatures associated with illicit drugs and explosives (high and low) has been designed to fit in the inlet of an ion mobility spectrometer (IMS). This is the first reporting of a fast and sensitive method for dynamic sampling of large volumes of air using planar solid phase microextraction (PSPME) incorporating a high surface area for absorption of analytes onto a sol−gel polydimethylsiloxane (PDMS) coating for direct thermal desorption into an IMS. This device affords high extraction efficiencies due to strong retention properties at ambient temperature, resulting in the detection of analyte concentrations in the parts per trillion range when as low as 3.5 L of air are sampled over the course of 10 s (absolute mass detection of less than a nanogram). Dynamic PSPME was used to sample the headspace over the following: 3,4-methylenedioxymethamphetamine (MDMA) tablets resulting in the detection of 12−40 ng of piperonal, high explosives (Pentolite) resulting in the detection of 0.6 ng of 2,4,6-trinitrotoluene (TNT), and low explosives (several smokeless powders) resulting in the detection of 26−35 ng of 2,4-dinitrotoluene (2,4-DNT) and 11−74 ng of diphenylamine (DPA).

Human bone and teeth fragments can be useful evidence when found in crime scenes and/or mass burials sites. The elemental and isotopic composition of these samples can provide information about environmental exposure events and could also be used to distinguish different individuals. The development and application of robust analytical methods for the quantification of trace elements in these biological matrices may lead to a better understanding of the potential utility of these measurements in forensic analyses.In this paper, we demonstrate the possibility of conducting quantitative analysis of trace metals found in bone remains and suggest a strategy to discriminate between individuals, based on this information. A LA-ICP-SF-MS method using non-matrix matched standard calibration was developed and optimized with bone standard reference materials (SRMs) and subsequently applied to the analysis of real samples. The developed method requires micrograms amount of sample (vs. milligrams required for solution-based analysis) while also reducing the analysis time and resulting in good accuracy (typically <10% bias) and precision (<15% RSD). Additionally, laser ablation allowed using spatial resolution analysis to assess the biogenic elemental composition in buried bone samples.Elemental analysis of bone samples from 12 different individuals provided better discrimination between the individuals when the femur and humerus bones were considered separately (42.7% correct classification with all bones vs. 75.2% and 63.1% for femur bones and humerus bones, respectively). Separation of individuals was achieved by elemental composition of whole teeth samples from 14 individuals, except one case where not all the teeth from the same individual were associated together. Separation of individuals was improved when using elemental composition of the enamel and dentine + cementum layers separately in a set of samples from 7 individuals. These are promising results for the use of elemental analysis by laser ablation ICP-MS for discrimination purposes.

Current methods used in document examinations are not suitable to associate or discriminate between sources of paper and gel inks with a high degree of certainty. Nearly non-destructive, laser-based methods using laser induced breakdown spectroscopy (LIBS) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to improve the forensic comparisons of gel inks, ballpoint inks and document papers based on similarities in elemental composition. Some of the advantages of these laser-based methods include minimum sample consumption/destruction, high sensitivity, high selectivity and excellent discrimination between samples from different origins. Figures of merit are reported including limits of detection, precision, homogeneity at a micro-scale and linear dynamic range. The variation of the elemental composition in paper was studied within a single sheet, between pages from the same ream, between papers produced by the same plant at different time intervals and between seventeen paper sources produced by ten different plants. The results show that elemental analysis of paper by LIBS and LA-ICP-MS provides excellent discrimination (> 98%) between different sources. Batches manufactured at weekly and monthly intervals in the same mill were also differentiated. The ink of more than 200 black pens was analyzed to determine the variation of the chemical composition of the ink within a single pen, between pens from the same package and between brands of gel inks and ballpoint inks. Homogeneity studies show smaller variation of elemental compositions within a single source than between different sources (i.e. brands and types). It was possible to discriminate between pen markings from different brands and between pen markings from the same brand but different model. Discrimination of ~ 96–99% was achieved for sets that otherwise would remain inseparable by conventional methods. The results show that elemental analysis, using either LA-ICP-MS or LIBS, provides an effective, practical and robust technique for the discrimination of document paper and gel inks with minimum mass removal (9–15 μg) and minimum damage to the document's substrate.

The detection of hidden explosives through their odors is of great importance to law enforcement agencies and trained canines have traditionally been used for this purpose. This paper reports the extraction of odor signature compounds characteristic of smokeless powders, followed by their detection by ion mobility spectrometers (IMS). Such a method enables the detection of odor compounds, complementing canine detection and allows for mass calibration of IMS instruments. The smokeless powder additives reported include diphenylamine (DPA), ethyl centralite, 2-ethyl 1-hexanol and 2,4-dinitrotoluene. The pre-concentration of these volatile odor chemicals from different commercial smokeless powders onto a solid phase microextraction (SPME) device followed by IMS analysis is demonstrated in this paper. Five samples of smokeless powder samples representing double-based and single-based powders from three popular commercial brands were chosen for this study. Diphenylamine was found to be a common additive among all the powders tested. The mass of the analytes in the headspace available for detection was determined from response curves of the corresponding standards. The response curves were generated by printing precise amounts of standards onto substrates and analyzing them. The absolute detection limits were also determined from these response curves and the values ranged from 0.12 to 1.2 ng for the standards. Typical extraction times ranged between 5 and 40 min and the mass of diphenylamine and ethyl centralite extracted at the lowest extraction times was found to be greater than the LOD of the compounds.

A simple, rapid and sensitive method was developed for the routine analysis of trace elements on sediments and soils by UV-ns-LA-ICP-MS. The homogenization procedure that reduces the particle size of the samples to less than 1 µm diameter was found to be a key factor to allow for a representative sampling of the bulk soil at the micro-scale and to improve reproducibility and cohesion of the sample without requiring the use of any binder. The elimination of binders simplified the sample preparation and avoided any undesirable dilution of the sample. SEM/EDX analyses were conducted to evaluate the efficiency of laser to sample interaction. Matrix effects and different quantitation strategies were employed to demonstrate the utility of the analytical technique. Sixteen elements were analyzed on soil and sediment samples and certified reference materials. Analytical results obtained by LA-ICP-MS were comparable to solution ICP-MS analysis in terms of accuracy, precision and limits of detection. Two independent proficiency tests for trace metals in soils were conducted to compare the performance of the method versus conventional digestion ICP and AA methods, obtaining z scores ≤ 3 for all elements measured by LA-ICP-MS. An overall bias between 8 and 15% was found, depending on the sample while the overall precision was found to be better than 5% RSD for all samples. Limits of detection were as low as 0.01 mg kg− 1.

The combined use of SIMION 7.0 and the statistical diffusion simulation (SDS) user program in conjunction with SolidWorks® with COSMSOSFloWorks® fluid dynamics software to model a complete, commercial ion mobility spectrometer (IMS) was demonstrated for the first time and compared to experimental results for tests using compounds of immediate interest in the security industry (e.g., 2,4,6-trinitrotoluene, 2,7-dinitrofluorene, and cocaine). The effort of this research was to evaluate the predictive power of SIMION/SDS for application to IMS instruments. The simulation was evaluated against experimental results in three studies: (1) a drift:carrier gas flow rates study assesses the ability of SIMION/SDS to correctly predict the ion drift times; (2) a drift gas composition study evaluates the accuracy in predicting the resolution; (3) a gate width study compares the simulated peak shape and peak intensity with the experimental values. SIMION/SDS successfully predicted the correct drift time, intensity, and resolution trends for the operating parameters studied. Despite the need for estimations and assumptions in the construction of the simulated instrument, SIMION/SDS was able to predict the resolution between two ion species in air within 3% accuracy. The preliminary success of IMS simulations using SIMION/SDS software holds great promise for the design of future instruments with enhanced performance.

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), micro X-ray fluorescence spectroscopy (μXRF), and laser induced breakdown spectroscopy (LIBS) are compared in terms of discrimination power for a glass sample set consisting of 41 fragments. Excellent discrimination results (> 99% discrimination) were obtained for each of the methods. In addition, all three analytical methods produced very similar discrimination results in terms of the number of pairs found to be indistinguishable. The small number of indistinguishable pairs that were identified all originated from the same vehicle. The results also show a strong correlation between the data generated from the use of µXRF and LA-ICP-MS, when comparing µXRF strontium intensities to LA-ICP-MS strontium concentrations. A 266 nm laser was utilized for all LIBS analyses, which provided excellent precision (< 10% RSD for all elements and < 10% RSD for all ratios, N = 5). The paper also presents a thorough data analysis review for forensic glass examinations by LIBS and suggests several element ratios that provide accurate discrimination results related to the LIBS system used for this study. Different combinations of 10 ratios were used for discrimination, all of which assisted with eliminating Type I errors (false exclusions) and reducing Type II errors (false inclusions). The results demonstrate that the LIBS experimental setup described, when combined with a comprehensive data analysis protocol, provides comparable discrimination when compared to LA-ICP-MS and μXRF for the application of forensic glass examinations. Given the many advantages that LIBS offers, most notably reduced complexity and reduced cost of the instrumentation, LIBS is a viable alternative to LA-ICP-MS and μXRF for use in the forensic laboratory.

Laser Induced Breakdown Spectroscopy (LIBS) is presented as a tool for the elemental analysis of glass in forensic applications. Two harmonics of the Nd:YAG laser at 266 nm and 532 nm were used as the irradiation source for the analysis of several glass standards and soda–lime glass samples of interest to forensic scientists. Both lasers were kept at a constant energy of 20 mJ and focused using a 150 mm focal length lens. A series of experiments were also conducted to determine the importance of wavelength on lens-to-sample distance (LTSD) at each wavelength. It was determined that the optimal LTSD was found at ~ 1–2 mm focused into the surface for both wavelengths yet the crater depth resulting from the irradiation at 266 nm was significantly deeper (112 µm) than that from the 532 nm laser (41 µm). In addition, the analytical performance of LIBS on 5 NIST glasses and 6 automobile glasses at both wavelengths is reported. Good correlation for the quantitative analysis results for the trace and minor elements Sr, Ba and Al are reported along with the calibration curves, in most cases R2 > 0.95, using absolute intensities at various emission lines. Although 266 nm resulted in more mass removal, the 532 nm produced greater emission intensities. A slightly higher plasma density was determined for irradiation by 532 nm using the Stark broadening technique in comparison to the 266 nm irradiation.

Forensic laboratories routinely conduct analysis of glass fragments to determine whether or not there is an association between a fragment(s) recovered from a crime scene or from a suspect to a particular source of origin. The physical and optical (refractive index) properties of the fragments are compared and, if a “match” between two or more fragments is found, further elemental analysis can be performed to enhance the strength of the association. A range of spectroscopic techniques has been used for elemental analysis of this kind of evidence, including inductively coupled plasma mass spectrometry (ICP-MS). Because of its excellent sensitivity, precision, and accuracy, several studies have found that ICP-MS methods (dissolution and laser-ablation) provide the best discrimination between glass fragments originating from different sources. Nevertheless, standard unit-resolution ICP-MS instruments suffer from polyatomic interferences including 40Ar16O+, 40Ar16O1H+, and refractory oxide 40Ca16O+ that compromise measurements of trace levels of Fe56+ and Fe57+, for example. This is a drawback in the analysis of glass fragments because iron has been previously identified as a good discriminating element. Currently, several techniques are available that enable reduction of such interferences. However, there are no data comparing detection limits of iron in glass using those techniques. The aim of this study was to compare, the analytical performance of high-resolution sector field inductively coupled plasma mass spectrometry (HR-SF-ICP-MS) and quadrupole ICP-MS equipped with a dynamic reaction cell (DRC-ICP-MS), for the detection of iron in glass, in terms of accuracy, precision, and method detection limits (MDLs). Analyses were conducted using conventional acid-digestion and laser-ablation methods. For laser-ablation analyses, carrier gases were compared to assess the effect on detection limits in the detection of iron isotopes. Iron polyatomic interferences were reduced or resolved by using a dynamic reaction cell and high-resolution ICP-MS. MDLs as low as 0.03 μg g−1 and 0.14 μg g−1 were achieved in laser-ablation and solution-based analyses, respectively. Use of helium as carrier gas improved detection limits for both iron isotopes in medium-resolution HR-SF-ICP-MS and in DRC-ICP-MS.

The authors have previously reported the use of laser ablation ICP-MS as a powerful analytical tool for elemental analysis of glass. LA is a simpler, faster and less intrusive sample introduction method than the conventional solution ICP-MS. Due to the minute amount of material removed in LA (∼300 ng, 50 μm crater size), the analyst should be aware of special sampling considerations such as characterization of the glass fragments originating from the “known” source, fragment size and selection of the area and surface of ablation.The purpose of this work was to evaluate the micro-homogeneity of the elemental composition of glass samples commonly found in crime scenes like containers, architectural windows and windshields. The set of glasses under study was comprised of 56 fragments originated from glass containers, 28 fragments from automobile windshields and 20 fragments from architectural windowpanes. All fragments were selected with a size smaller than 2 mm2 in order to simulate the typical glass fragments transferred from the crime scenarios. A Nd:YAG laser, 266 nm, flat top beam profile was used in single point mode sampling 50 μm spot size for 50 s at 10 Hz (500 shots). In this study, 29Si was used as an internal standard and the standard reference material, SRM NIST 612, was used as a single point external calibrator. In addition, SRM 621 was used as another control standard for the containers set and SRM 1831 for the automobile and architectural window sets due to their very similar matrix with the samples of interest. For each set of glasses, the mean values and standard deviation of 10 replicates (n = 10) of a single fragment were compared with the values obtained from 10 (n = 10) different fragments of glass within the area of interest in order to evaluate whether or not the variation within a glass was bigger than the variation due to the method. In addition, a subset of tempered glasses was evaluated to perform an elemental composition profile within different depths of the fragments. Single shot (one laser pulse per analysis) was also evaluated and its limitations for the forensic analysis of glass are also presented. The results show that float glass is homogenous even at the micro-range level allowing LA-ICP-MS as an alternative technique to perform elemental analysis of glass. However, the variation of elemental composition of headlamps and containers is larger over the source than the instrumental variation due to inherent heterogeneity and therefore specific statistical methods are recommended to compare the glass samples.

The characteristic ions or the parent ion resulting from ionization can be isolated in an ion trap and subjected to further fragmentation during a gas chromatography–tandem mass spectrometry (GC/MS/MS) experiment. This approach can improve the selectivity and sensitivity of explosive compounds over gas chromatography–mass spectrometry (GC/MS) by improving the differentiation of the target compounds from interfering and co-eluting compounds and reducing the background noise within an explosive debris sample. The optimization of the operating parameters for GC/MS and GC/MS/MS experiments with an ion trap mass spectrometer were conducted using a mixture of explosive compounds and 3,4-dinitrotoluene as an internal standard. The level of detection (LOD) and limit of quantitation (LOQ) for these compounds was determined by GC/MS with electron ionization, GC/MS with positive chemical ionization, and GC/MS/MS with positive chemical ionization. The LOD range was found to be 3.6 pg for 2,4-dinitrotoluene to 2.23 ng for hexahydro-1,3,5-trinitro-s-triazine (RDX) using GC/EI/MS; 0.4 pg for 2,4-dinitroltoluene to 19.0 pg for 1,3,5-trinitrobenzene using GC/PCI/MS; and 0.5 pg for 4-nitrotoluene to 41.4 pg for RDX using GC/PCI/MS/MS. The LOD results for GC/PCI/MS and for GC/PCI/MS/MS are very similar for most of the compounds except the GC/PCI/MS LOD results are lower for RDX and 1,3-dinitrobenzene while the GC/PCI/MS/MS LOD results are lower for 1,3,5-trinitrobenzene. The GC/PCI/MS/MS method offers improved selectivity when analyzing real world samples containing interfering products and matrix noise thereby improving sensitivity for complex samples.

The use of aerosol defense sprays has increased as a means of self-defense and as a weapon in the commission of a crime. The residue of these sprays is often left behind as physical evidence on a victim's clothing or personal belongings. As the popularity of self-defense weaponry increases, so does the likelihood that it will be encountered in forensic casework. The extraction, recovery from fabrics, and identification of residue from defense sprays is described. The commonly used extraction method of liquid–liquid extraction is compared to solid phase microextraction (SPME) to recover capsaicin and dihydrocapsaicin from cotton swabs. The use of SPME resulted in lower limits of detection and greater recovery efficiency when compared to solvent extraction. SPME also provided more consistent recovery and less variability when compared to solvent extraction. The effect of use of various types of evidence packages on the preservation of this type of evidence is also reported. The collection and analysis of hand swabs after normal discharge of pepper spray canisters was studied indicating the low persistence of these compounds on the hands of the person conducting the spraying. Finally, the results of a real case whereby solvent–solvent extraction did not provide the necessary sensitivity for extracting the capsaicin compounds on the garments of a victim of an alleged spraying and the SPME extraction provided the recovery and identification of the compounds is also presented.

Glass fragments recovered from crime scenes are usually very small and therefore the amount of sample available to conduct forensic analyses is limited. Elemental analysis using conventional digestion methods consumes at least 2–3 mg of glass per replicate. LA-ICP-MS requires 10,000 times less glass consumption per analysis (∼280 ng), and therefore the sample remains practically unaltered. Typically, the recovered fragments (unknowns) are 0.1–1 mm in length, while the “known” samples are usually larger, i.e. a broken fragment from a windshield (>3 mm). For bulk digestion analysis, the difference in fragment size does not present a problem for elemental comparisons – other than requiring at least 6 mg for triplicate analysis – because the sample is crushed and homogenized before weighing. Laser ablation sampling results in the creation of small craters (∼50 μm diameter and 80 μm deep) drilled into the sample due to the interaction of the laser with the glass target. This study aims to evaluate whether the quantitative elemental analysis using the LA sampling method is affected by the size of the glass fragment due to differences in heat dissipation and surface–laser interaction. The analytical method employed for the analysis of glass by LA-ICP-MS had previously shown to possess the same or better performance than dissolution ICP-MS methods in terms of accuracy, precision, limits of detection and discrimination power. A 266 nm Nd:YAG laser with a flat top beam profile was used in single point mode sampling a 50 μm spot size for 50 s at 10 Hz. Standard glass reference materials SRM 612 and SRM 610 were selected to conduct this work in order to account for different concentration ranges and different opacities of the samples. The set under study was comprised of seven fragments originating from each standard at different sizes and shapes ranging from 6 to 0.2 mm length. Analysis of variance (ANOVA) followed by the Tukey's honestly significant different test (HSD) was used for data analysis. The results show that there is no significant difference in the elemental composition of different sized fragments. The conclusions, however, cannot be generalized for fragments measuring less than 0.2 mm × 0.1 mm.

Glass fragments from 81 automobile side windows were collected and analyzed by the FBI Laboratory using ICP-AES in 1991. The FBI selected 9 elements (Al, Ba, Ca, Fe, Mg, Mn, Na, Sr and Ti) to use for discrimination among the glass samples. This multi-element discrimination showed a significant improvement in the discrimination statistics over using only refractive index (RI) measurements. Oak Ridge National Laboratory (ORNL) recently analyzed fragments from 76 of the original side window fragments using inductively coupled plasma mass spectrometry (ICP-MS). The ICP-MS analyses measured 45 elements using a hierarchical sampling scheme to estimate variances due to sampled population (VP), variance due to sample dissolution and within sample heterogeneity (VD), and variance due to replicate measurements (VM). The between-to-within ratio [B/W = VP/(VD + VM)] afforded a measure of the variance within the population to that in the analytical measurement, providing a first approximation of the discriminating power of each element. Florida International University updated the RI measurements on 72 available glass fragments. These RI measurements along with ICP-AES and ICP-MS elemental analyses were used for pairwise comparisons of all possible pairs of the 72 glasses that had a complete set of measurements. The pairwise comparisons used Tukey's HSD method to compare RI and element-by-element discrimination potential of ICP-AES and ICP-MS for analyzing glass in forensic casework.

•Identification of VOCs from marijuana using the CMV as a sampling and preconcentration device.•Marijuana can be differentiated from other plants by the chemical profile.•The distinguishing compounds included α-santalene, valencene, and β-bisabolene.•THC and cannabinol were also found present in the headspace of marijuana.The ability to rapidly detect illicit drugs, such as marijuana, is critical to policing legislation across the country. However, it is often difficult to distinguish or identify small quantities of drugs in large spaces without the aid of trained canines. A new device, the capillary microextractor of volatiles (CMV), has the potential to provide rapid detection due to its ability to collect and preconcentrate volatile organic compounds (VOCs) directly from air within minutes. Analysis of the captured compounds can then be performed using a gas chromatography–mass spectrometer (GC–MS). This study focuses on the detection of marijuana volatiles using the CMV as a sampling and preconcentration device given the hypothesis that marijuana will have a distinct chemical profile, or collection of VOCs, that distinguishes it from related plants and other products that could emit similar compounds. Volatile compounds from the headspace of marijuana, related plants, and hemp products were extracted using the CMV and analyzed with GC–MS. The compounds identified and the chemical profiles of each sample were then compared to the volatiles found in the headspace of authentic marijuana samples. The findings presented here suggest that marijuana plants emit volatiles that are readily distinguished from the other samples tested in this study. The distinguishing compounds included α-santalene, valencene, and β-bisabolene. In some cases, THC and cannabinol were also present in the headspace of marijuana. Although these findings support the hypothesis that marijuana has a distinct chemical VOC signature, further work to create a larger database of potential plants and materials is recommended prior to routine use of the CMV coupled to a GC–MS in forensic casework.Graphical abstractDownload high-res image (66KB)Download full-size image

•Temporal sequence could not be determined from the study.•Luminescent compounds were identified in formulation of inks.•Interlaboratory tests incorporated mass spectrometric and chromatographic techniques.•Crystal violet was identified in migration regions of inks in crossed-line intersections.Several analytical instrumental techniques have been tested and utilized in an effort to determine the sequencing in crossed-line intersections (CLI) in order to gain insight into the eventual development of a standardized method to determine temporal sequence of line writing. One important facet of this study was to determine the chemical identity of the luminescent compounds present in the formulation of inks to better understand the interaction of different inks in crossed-line intersections. This study involved independent analyses of a number of inks by three laboratories. A combination of Thin Layer Chromatography (TLC), Gas Chromatography Mass Spectrometry (GC/MS), High Performance Liquid Chromatography (HPLC), Matrix-Assisted Laser Desorption Mass Spectrometry (MALDI-MS), Direct Analysis in Real Time Mass Spectrometry (DART-MS), and Liquid Chromatography Mass Spectrometry (LC-MS) were implemented by the three laboratories in order to characterize the luminescent components of inks present in crossed-line intersections. A combination of luminescent compounds including Crystal Violet and Methyl Violet were characterized and identified to be present in mixtures in the ink formulations utilizing each of the analytical techniques included in this study. However, the temporal sequence of deposition of inks present in crossed-line intersections could not be determined. The protocol described here allows for the isolation and characterization of luminescent compounds present in the formulation of inks to varying degrees, and the information presented here can be used in the future establishment of a standard protocol for the identification of luminescent compounds in inks.Download high-res image (118KB)Download full-size image

•A new sampling device for dynamic headspace sampling of VOCs and smokeless powders is described.•A cryofocusing device consisting of a Peltier-cooled module that operates down to −10 °C was employed.•The CMV analysis of 17 VOC’s is assessed using the criteria established by the EPA.•CMV performance was demonstrated for detection of markers above the headspace of smokeless powder.A novel field sampling device for fast, sensitive, dynamic headspace sampling of volatile organic compounds (VOCs) and smokeless powders from air is described. The capillary microextraction of volatiles (CMV) is an inexpensive, preconcentration technique that results in fast sampling times (as low as 2 min) with high efficiency and sensitivity. Analysis of the CMV with GC–MS is achieved with a thermal desorption probe to introduce the CMV directly into the injection port of a GC. A cryofocusing device consisting of a Peltier-cooled module that operates down to −10 °C was employed to improve the extraction efficiency of the CMV for sampling both VOCs and smokeless powders.The method performance using the CMV for the analysis of 17 VOC’s, including the BTEX compounds (Benzene, Toluene, Ethylbenzene, and Xylenes) is demonstrated using the criteria established by the Environmental Protection Agency (EPA) for sorbent tube sampling of toxic organic compounds in ambient air (EPA TO-17). Experimental results with known standards yield absolute mass detection limits ranging from 2.0 to 4.6 ng for the target compounds, in a 2 L air sample. A 35–100% improvement in the analytical performance was achieved by sampling at −10 °C, in comparison to 20 °C, for most compounds. Using cryofocusing conditions, precision of 8–53 %RSD was achieved for headspace extraction for the majority of the compounds with recoveries of as much as 37% and low breakthrough. Furthermore, the headspace calibration curves show a linearity of 0.951 or better for the target compounds, suggesting the quantitation capabilities of the CMV device.The CMV method performance was further demonstrated for the detection of markers above the headspace of smokeless powder. Experimental results with known standards, yield method detection limits of 2.0 ng and 1.3 ng for nitroglycerine (NG) and diphenylamine (DPA), respectively, in a 2 L air sampling volume followed by simultaneous SIM mode GC–MS analysis. Using cryofocusing conditions for the headspace extraction of Hodgdon smokeless powder, a 29–38% improvement in the analytical performance of NG was achieved with 18 %RSD precision, by sampling at 2.5 °C to −10 °C, in comparison to room temperature at 20 °C.Download high-res image (123KB)Download full-size image

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.