Forensic Chemistry最新文献

Soil, as a surviving trace after contact and transfer between contacting surfaces at a crime scene, can be recovered and analyzed to infer the presence of persons or tools at the scene and prior activity leading to its deposition. With its vast diversity and heterogeneity, it varies in composition from place to place, providing a basis for trace examiners to distinguish visually similar-colored soils. Unlike countries with native topsoil, Singapore’s urban lands are commonly filled with man-altered and man-transported soil, with relatively little known about the variations of soil’s characteristics within a small, localized area. The current study surveyed the soil’s elemental variability in Singapore parks, which are green spaces for public leisure use. Past installations of recreational facilities and landscaping with fast-growing vegetation in parks inevitably cause disturbance to the original natural soil and mixing with extraneous soil, further contributing to the heterogeneity of the park’s topsoil composition. In our sampling approach, visually similar-colored surface soils were collected from within a 1-m² site, sites in proximity within a park, and parks across Singapore. The collected soils were dried and sieved into clay- and silt-size fractions for elemental analysis using WDXRF and SEM/EDS. To examine the extent of the spatial elemental variability, we adopted three-sigma interval match criteria and a discriminative model incorporating relative data, square root values and the Canberra distance measure for data processing and pairwise comparison of soil samples. The study also aimed to develop soil databases encompassing soils across Singapore with the intent of understanding the value of soil evidence within a local context.

The identification of organic and inorganic components used to produce homemade explosives (HMEs) remains a challenge for forensic analysts due to their diverse physicochemical properties that require different instrumentation. This study aims to explore the combined use of direct analysis in real time-mass spectrometry (DART-MS) and Raman microscopy to provide a rapid and reliable analysis of a variety of intact explosives with minimal sample preparation, including 2,4,6-trinitrotoluene (TNT), pentaerythritol tetranitrate (PETN), seven inorganic oxidizing salts, and five smokeless powder constituents. While both techniques were well-suited for the analysis of TNT and PETN, DART-MS had the advantage of being more sensitive compared to Raman spectroscopy for the identification of the organic components contained in smokeless powder. Even though the identification of ammonium-based salts using DART-MS could be achieved, the analysis of low-volatility compounds, such as the inorganic oxidizing salts, was more straightforward with Raman microscopy and did not require sample preparation. This study demonstrates the benefits and limitations of combining Raman microscopy and DART-MS for the analysis of intact explosives and precursors. Using this combined approach enabled the rapid identification of various organic and inorganic explosives and precursors with minimal sample preparation.

The cadaveric volatilome of terrestrial decomposition, including buried corpses, has been extensively studied in recent taphonomic research. However, there has been comparatively less attention given to the volatile organic compounds associated with submerged vertebrate remains. This decaying process is distinct, as evidenced by the succession of decay stages that significantly differ from terrestrial decomposition. Indeed, five stages can be delineated: fresh, early floating, floating decay, deterioration, and sunken remains. Due to the unique nature of underwater decomposition, we anticipate the release of different cadaveric volatiles from submerged remains. In this study, we characterize the volatile compounds emitted during underwater decomposition and that reach the surface. Rat cadavers were placed individually in glass chambers filled with water. The volatiles released at the surface were subsequently collected three times per week over the course of a month. Two types of water, fresh and marine, were used to assess the potential influence of the salinity level on the cadaveric volatilome. A total of 33 volatile compounds were identified, with the majority having previously been reported in the headspace of cadavers undergoing decomposition in a terrestrial environment. Among these compounds, those containing sulfur were the most abundant, with dimethyl disulfide being the major one. Our findings did not reveal any discernible impact of salinity levels on the volatile profile, which was, however, affected by the specific decaying stage. Notably, 3-methyl-indole emerged as a promising candidate for distinguishing between the first two stages of decomposition and the subsequent third stage.

Forensic investigations of explosives in post-blast and trace scenarios often utilize gas chromatography-mass spectrometry (GC–MS). Many high explosives (e.g., trinitrotoluene) provide structurally significant ions so that a compound can be confidently identified by GC–MS; however, GC–MS only provides functional group identification for the presence of nitrate esters (e.g., nitroglycerin (NG)), a class of high explosives that is frequently encountered in forensic casework. Nitrate esters vary drastically and are much more accurately identified by their component alcohol structure rather than merely the detection of the nitrate and nitrite ions. Herein, we demonstrate a two-step derivatization reaction requiring no purification steps or advanced sample preparation and characterize several of the reaction byproducts created along with the desired reaction product. In this process, nitrate esters are initially reduced to their component alcohol, and then subsequently silylated. The resulting product, when submitted to GC–MS with positive ion mode chemical ionization, provides mass spectra that characterizes the component alcohol by the pseudo-molecular ion of the reaction product. GC–MS with negative ion mode chemical ionization confirms the presence of a nitrate functional group by the characterization of the unreacted starting material. These results combine to identify nitrate esters in forensic settings, and as a proof of concept, we demonstrate the applicability of the derivatization reaction to pentaerythritol tetranitrate (PETN), NG, and erythritol tetranitrate (ETN) standards, as well as a formulated composition containing PETN-SEMTEX 1A, homemade ETN, and post-burn samples.

Marijuana and hemp are different cultivars of the species, Cannabis sativa. Trichomes within these genetically distinct forms result in different chemical constituents within the plant matrix. While drug-type cannabis yields higher total Δ9-THC concentrations, industrial or consumer-based hemp products are typically rich in cannabidiol or CBD-rich. Regulatory changes following the passage of agricultural legislation in the United States defines hemp as C. sativa containing no more than 0.3 % Δ9-THC on a dry weight basis. This threshold, which effectively differentiates legal hemp from illegal marijuana, presents a challenge to operational forensic laboratories. In this report we describe a decision-point assay to differentiate hemp from marijuana using a 1 % threshold. Methanolic extracts of C. sativa were analyzed using gas chromatography-mass spectrometry (GC–MS) using a deuterated analog (Δ9-THC-D3). Synchronous selected ion monitoring (SIM) and full scan acquisition was used for targeted analysis of Δ9-THC at the decision-point. Assay performance was evaluated in terms of limit of detection, linearity, carryover, selectivity, precision, accuracy and extract stability. Two analytical approaches are presented. Extraction efficiencies of Δ9-THC from plant matrix were 80–92 %, and decarboxylation of Δ9-tetrahydrocannabinolic acid (THCA) was 67 %. Interferences arising from the cyclization of CBD to produce Δ9-THC in the GC inlet were addressed using concentrations in excess of those typically encountered in plant samples. Accuracy was established across the specified range of the assay using known reference materials containing 0.12 to 10.1 % Δ9-THC. No false positive or negative results were identified (n = 140) using both analytical approaches.