Forensic Chemistry最新文献

In the ensuing investigation after an explosion, determining the explosive used is of prime importance to establish investigative leads. Post-blast samples have many interferences and considerations that make quick, reliable identification a challenge. The use of a novel subsampling technique with DART-HRMS provides the ability to quickly detect and identify explosive residue after detonation. Simulated improvised explosive devices were constructed with a variety of materials and detonated with the help of the Montgomery County Fire Marshal’s Office (TX). Post-blast debris was subsequently collected and swabbed with a novel subsampling technique, utilizing filter paper. This filter paper was then introduced into the DART gas stream, with an internal standard to minimize potential false negatives. After introducing explosive residue from swabbed post-blast substrates, characteristic ions of selected constituents of smokeless powder including diphenylamine, ethyl centralite, di-n-butyl phthalate, and nitroglycerin were detected and confirmed through comparison of accurate mass measurements to theoretical exact masses. Additionally, characteristic ions of 2,4,6-trinitrotoluene (TNT) and Royal Demolition eXplosive (RDX) were also detected using this technique. Overall, the detection of characteristic ions was more successful when recovering residue from plastic compared to wood or metal, with success rates routinely at 100%. Implementing this screening technique enables rapid detection and reliable identification of explosive residue in a detonation incident. The developed subsampling technique provides practitioners with a practical method of screening post-blast debris in a laboratory setting, requiring minimal sample preparation.

Occasionally, trace evidence¹-casework faces major challenges, as not only suitable analytical methods must be available for relevant technical products and their traces, but background information regarding market or manufacturing processes must also be collected. Furthermore, analytical and forensic benefit are supposed to go together, in certain cases even under great time pressure. Given the focus of forensic service providers on individual traces, trace evidence work areas may not always be well prepared, particularly for products for which there are no collection traditions. On the basis of three fictitious case studies, an approach based on division of labor is presented and its advantages and disadvantages are discussed.

Post-explosion residue analysis is vital in forensic chemistry, providing valuable insights into incidents involving explosives. One significant challenge in this field is preserving samples for long-term storage for reanalysis. Presently, many laboratories conducting post-explosion analyses worldwide do not retain samples for reanalysis purposes, since the extraction process for sample preparation often necessitates the complete consumption of the scarce material. Even in cases where a portion of the material remains, such as a swab, it is difficult to ensure its representativeness and select a specific portion for preservation. One possible solution to overcome this challenge is to consider preserving the extracts used in the analyses for potential reanalysis. However, the stability characteristics of these extracts are currently unknown. The results presented in this article provide valuable insights into the feasibility of long-term storage for samples containing target analytes in extracts from post-explosion/burning residues of frequently encountered fuel-oxidizer explosive mixtures, such as flash powder, explosive emulsion, and black powder. These results shed light on the potential viability of preserving such extracts for future reanalysis, offering promising prospects for enhancing forensic investigations in this field. Based on the current findings, it has been demonstrated that the aqueous extracts can be effectively preserved as long-term storage samples for a minimum of 24 months, encompassing all the studied explosives. Only cyanate ion showed significant degradation among the 27 compounds studied. Additionally, the organic extract, specifically in the case of emulsion explosive, can be maintained for at least 12 months.

A series of N,N-disubstituted piperazines were synthesized containing the structural elements of meta-chlorophenylpiperazine (mCPP) in combination with methoxybenzyl-, and dimethoxybenzyl substituents to yield nine N,N-disubstituted piperazine compounds. These nine potential designer-like drug analogs were prepared based on common designer trends and regioisomeric differentiation was based on gas chromatography-mass spectrometry (GC–MS) and gas chromatography-vapor phase infrared (GC–vpIR) studies. The compounds in this study have not been reported as drugs of abuse at this time. However, commercial availability of precursor chemicals including mCPP suggests the possibility of further designer exploration. Capillary GC separation showed the regioisomers to elute according to the position of aromatic ring substitution and/or the degree of substituent crowding on the aromatic ring. Numerous electron ionization (EI) mass spectral fragment ions occur via processes initiated by one of the two nitrogen atoms of the piperazine ring. The major EI-MS fragment ions observed in all nine spectra occur at m/z 195 from the loss of the substituted benzyl radical and the cation at m/z 56 (C₃H₆N)⁺ from the piperazine ring. Unique radical cations at m/z 136 and m/z 152 are characteristic of the 2,3- and 3,5-dimethoxybenzyl isomers, respectively. The vapor phase infrared spectra for all nine compounds show a strong absorption band in the 1591–1593 cm⁻¹ region indicative of the chloroaniline moiety. Numerous bands in the 1600–650 cm⁻¹ region provide data for the differentiation of the methoxy and dimethoxybenzyl ring substitution patterns. Thus, a combination of EI-MS and vapor phase IR allow for the differentiation and specific identification of each regioisomer in this study.

Benzodiazepine (BZD) misuse has increased in the last decade, making its occurrence in criminal cases more commonplace. The detection of BZD in complex biological samples is challenging since they are usually found in small concentrations, requiring the development of sensitive and fast-to-execute methods. In this study, the application of direct analysis in real time – high-resolution mass spectrometry (DART-HRMS) was evaluated in the detection of 10 benzodiazepines (diazepam, oxazepam, chlordiazepoxide, temazepam, alprazolam, flunitrazepam, bromazepam, clonazepam, lorazepam, and midazolam) in ante and postmortem blood samples. Moreover, an ultrasound-assisted dispersive liquid–liquid microextraction (UA-DLLME) approach was developed by full factorial design as a clean-up step before the DART-HRMS analysis. DART-HRMS was capable of qualitative detection of all evaluated BZD in raw antemortem blood samples at concentrations as low as 10 µg mL⁻¹. The UA-DLLME DART-HRMS approach was linear for the 10 BZD in the range of 1 to 10 µg mL⁻¹, with recoveries ranging from 78.5 to 119.5 %, a precision lower than 36 % at 1 µg mL⁻¹, and limits of detection varying between 0.25 and 0.50 µg mL⁻¹. Moreover, the UA-DLLME DART-HRMS method was efficiently applied to postmortem blood samples from criminal cases, enabling the detection of BZD. The developed method facilitated the analysis of 10 BZD in ante and postmortem blood samples, offering a quick sample extraction that linked to the DART-HRMS can be used as a fast and reliable triage method for regulatory screening purposes and could be readily integrated into routine forensic analysis workflows in a high throughput manner.

Establishing links between starting materials and products is highly valuable in the investigation of the use of toxic chemicals for illicit purposes. In this study, impurity profiling was performed on starting materials and their synthesis product, 2-([dimethylamino]methyl)pyridin-3-yl dimethylcarbamate, an intermediate compound in the production route for the carbamate class of Chemical Warfare Agents. The aim was to link the five commercial starting materials to the correct synthesis products. Initially, the intermediate compound was synthesized using different batches of the two starting materials (2 plus 3 batches), producing six unique combinations. All synthesis batches and the different starting materials were analysed by gas chromatography-high resolution mass spectrometry (GC-HRMS). Chemometrics analyses were conducted with principal component analysis and orthogonal projections to latent structures discriminant analysis to extract chemical impurity profiles and to build supervised classification models.

Additionally, 12 test set samples, produced using the same starting materials by two different chemists in another laboratory, were analysed by GC-HRMS. A classification model able to distinguish all supplier combinations was successfully created and used to link the test set samples to their corresponding starting material.

Furthermore, a new set of synthesis samples was extracted with a work-up procedure before analysis to investigate the effect of higher sample purity on the classification model. The results show that linking the synthesis products to their starting materials was successful for one of the starting materials, despite the purification procedure.

Fire debris is collected and analyzed to determine whether volatile hydrocarbons of ignitable liquids (IL) are present. Typically, the hydrocarbons from fire debris are separated from the debris by adsorption onto activated carbon. Laboratory generated fire debris were sampled by adsorption onto activated charcoal strips (ACS) where half of the ACS was analyzed by gas chromatography – mass spectrometry (GC–MS) and the other half was preserved for 14 years [1,2]. Reference ignitable liquids are important in the detection and identification of ignitable liquid residues (ILR) from fire debris [3]. Reference IL contain 400 µl of IL adsorbed onto 0.5 g of granular activated carbon (GAC) and were preserved for 21 years. Comparisons of the chromatographic profiles at Day 0 and Year X (X = 14 or 21) were performed by Spearman rank correlation of selected peak’s intensities and visual inspection to determine how well these samples were preserved. The fire debris samples on ACS had an average Spearman rank correlation coefficient of 0.90 with a standard deviation of 0.11. Thirty-six percent of them demonstrated no change in the chromatographic profile and 64 % of them demonstrated minimal desorption in the chromatographic profile. The GAC samples had an average Spearman rank correlation coefficient of 0.95 with a standard deviation of 0.12. Eighty-two percent of them demonstrated no change in the chromatographic profile. This study reveals that hydrocarbons of ignitable liquids on activated carbon following established preservation procedures remain useful for forensic purposes after long-term storage.

Current hair testing methods, which mainly rely on quantification of parent drug analytes, have difficulty distinguishing drug deposited into hair through physiological processes from drug deposited onto hair via external contamination. Using conjugated phase II metabolites to differentiate between drug use and possible external contamination is advantageous as they are unlikely to be degradation products or synthesis byproducts. In this study, 97 specimens were analyzed for opioid glucuronides and the corresponding parent drugs. Morphine-3-glucuronide and morphine-6-glucuronide were the most prevalent glucuronides and were detected in 82 % of specimens with morphine concentrations ≥ 200 pg/mg (n = 33). Median glucuronide to parent ratios were 0.65 % and 1.12 % for morphine-3-glucuonide and morphine-6-glucuronide respectively. Codeine-6-glucuronide was detected in 100 % of specimens with a codeine concentration ≥ 200 pg/mg (n = 8), with a median glucuronide to parent ratio of 2.21 %. Hydromorphone-3-glucuronide was detected in 75 % of specimens with hydromorphone ≥ 200 pg/mg (n = 4) with a median glucuronide to parent ratio of 1.24 %. Oxycodone-3-glucuronide was detected in 37 % of specimens with oxycodone ≥ 200 pg/mg with a median glucuronide to parent ratio of 0.91 %. No hair specimens with a parent concentration less than LOD had a corresponding glucuronide present. This study shows that a 1 pg/mg cutoff for glucuronides provides similar sensitivity as the currently recommended 200 pg/mg cutoff for morphine, codeine, and hydrocodone.

This paper summarises the available literature data for the evidential evaluation topics of transfer (196 experiments), persistence (63 time series), contamination (1515 samples), and background prevalence (2158 samples) of inorganic gunshot residues (IGSR). In-house data on IGSR transfer, and the prevalence and persistence of IGSR on different types of glove are also contributed.

Combining new and previously published data in a meta-analysis, we report the following findings: The median transfer rate of IGSR was 11 % and the probability distribution of contact transfer was modelled using a Beta distribution. The half-life of IGSR on hands was estimated at 52 min. On gloves, decay followed a two-phase process with the slower process proceeding at a decreased rate compared to on hands (t_1/2,slow = 77 min). The occurrence of characteristic IGSR on the hands of police officers was modelled using a generalised Pareto model (GPM). Combining the prevalence and the transfer probability models, a product probability distribution model was established. The product model estimates the probability of finding any amount of IGSR post-arrest on previously clean hands, estimating 8 % probability of non-zero transfer. Characteristic IGSR detected on the general public (1 % positives), on at-risk individuals (2 % positives), and in public places (0 % positives) showed low background levels. The likelihood of finding any amount of IGSR on the general public (at-risk included) was modelled using a GPM giving a 1.3 % probability of finding at least one, and 0.2 % probability to find more than three characteristic IGSR on the general public.

Fibres are prevalent and can be encountered as trace evidence in various situations. In cases of rape and physical assault, analyzing trace fibre components and assessing their transferability can establish connections between individuals and crime scenes or between perpetrators and victims. This study involved Attenuated Total Reflectance – Fourier Transform Infrared (ATR–FTIR) characterization of 104 fibre samples, including natural fibres like cotton and wool (43 samples) and terry wool and synthetic fibres (61 samples). Prominent peaks in different textile fibre spectra were primarily found in the fingerprint region (1800–450 cm⁻¹). To simplify analysis, the spectral data was reduced to principal components, and sample discrimination was performed using Python’s PyCaret package. Multiple machine learning algorithms were explored for differentiating fibre samples, and the most effective one was selected for further validation. This study demonstrates the feasibility of developing an ATR-FTIR database for additional textile fibre samples, aiding in the detection of unknown or suspect fibres in the future.