Analysis of the lipidomic profile of vegetable oils and animal fats and changes during aging by UPLC-Q-exactive orbitrap mass spectrometry.

Vegetable oil and animal fat residues are common evidence in the cases of homicide, arson, theft, and other crimes. However, the lipid composition and content changes during aging on complex carriers remain unclear. Therefore, this study dynamically monitored the lipid composition and content changes during aging of 13 different types of vegetable oils and animal fats on five different carriers using the UPLC-Q-Exactive Orbitrap MS method. A total of 6 subclasses of 93 lipids including lysophosphatidylcholine (2 species), phosphatidylcholine (2 species), diglyceride (5 species), triglyceride (81 species), acylGlcCampesterol ester (2 species), and acylGlcSitosterol ester (1 species), were first identified in fresh vegetable oils and animal fats. By comparing the LC-MS/MS chromatograms of fresh vegetable oils and animal fats, it was found that there were significant differences between the chromatograms of vegetable oils and animal fats, but it was difficult to distinguish between the chromatograms of vegetable oils or animal fats. After aging at 60 °C for 200 days, there was a significant decrease in the content of diglyceride, triglyceride, acylGlcCampesterol ester, and acylGlcSitosterol ester, while the content of lysophosphatidylcholine and phosphatidylcholine initially increased and then decreased. Furthermore, statistical analysis of lipid differences between vegetable oils and animal fats was performed using cluster heat maps, volcanic maps, PCA, and OPLS-DA. On average, 33 significantly different lipids were screened (VIP > 1, p < 0.05), which could serve as potential biomarkers for distinguishing vegetable oils and animal fats. It was found that the potential biomarkers still existed during aging of vegetable oils and animal fats (100 and 200 days). This research provides important reference information for the identification of vegetable oil and animal fat residues in complex carriers at crime scenes.

Robotic-OCT guided inspection and microsurgery of monolithic storage devices.

Data recovery from monolithic storage devices (MSDs) is in high demand for legal or business purposes. However, the conventional data recovery methods are destructive, complicated, and time-consuming. We develop a robotic-arm-assisted optical coherence tomography (robotic-OCT) for non-destructive inspection of MSDs, offering ~7 µm lateral resolution, ~4 µm axial resolution and an adjustable field-of-view to accommodate various MSD sizes. Using a continuous scanning strategy, robotic-OCT achieves automated volumetric imaging of a micro-SD card in ~37 seconds, significantly faster than the traditional stop-and-stare scanning that typically takes tens of minutes. We also demonstrate the robotic-OCT-guided laser ablation as a microsurgical tool for targeted area removal with precision of ±10 µm and accuracy of ~50 µm, eliminating the need to remove the entire insulating layer and operator intervention, thus greatly improving the data recovery efficiency. This work has diverse potential applications in digital forensics, failure analysis, materials testing, and quality control.

Study of the Power Generation Performance of Impact Piezoelectric Energy Capture Devices.

In order to solve the problem of conventional energy shortages, a non-resonant impact piezoelectric energy capture device using a (polyvinylidene fluoride) piezoelectric film at low frequency is proposed, and related theoretical analysis and experimental studies are conducted. The device has a simple internal structure, is green and easy to miniaturize, and is capable of harvesting energy at low frequencies to supply energy to micro and small electronic devices. First, to verify the feasibility of the device, the structure of the experimental device is modeled and dynamically analyzed. Then the modal, stress-strain, and output voltage of the piezoelectric film are simulated and analyzed using COMSOL Multiphysics simulation software. Finally, the experimental prototype is built according to the model, and the experimental platform is constructed to test the relevant performance. The experimental results show that the output power produced by the capturer varies within a certain range when the capturer is excited externally. With an external excitation force of 30 N, a piezoelectric film bending amplitude of 60°, and a piezoelectric film size of 45 × 80 mm, the resulting output power voltage is 21.69 V, the output current is 0.07 mA, and the output power is 1.5176 mW. This experiment verifies the feasibility of the energy capturer and provides a new idea for powering electronic components.

Determination of disperse dyes on polyester fibers by UHPLC-Orbitrap MS.

The determination of fiber dyes is important in forensic investigations. Although a variety of fiber dyes detection methods have been established, the sensitive and accurate determination of trace fiber dyes remains a challenge due to the possible interferences caused by complex environmental matrix and various fiber additives. Orbitrap mass spectrometry (Orbitrap MS) is a type of high-resolution mass spectrometry with high qualitative accuracy and detection sensitivity which highly meet the identification requirements of fiber dyes in real cases. However, the application of Orbitrap MS in fiber dye analysis is limited. In this regard, this study used polyester fiber, which is the most commonly-found fiber in forensic cases, as a model and established a UHPLC-Orbitrap MS method to analyze disperse dyes on polyester fibers. Using the optimized UHPLC-Orbitrap MS method, nine disperse dyes were accurately identified and well separated, and the limits of detection ranged between 0.1 ng/mL and 5.0 ng/mL. The developed method was applied to analyze actual fiber samples, and dyes from single fibers of 1 mm in length could be accurately detected. The established method is sensitive, accurate, and demonstrates good application prospects.

In situ identification of TATP and DADP particles collected with transparent tape by Raman spectroscopy and imaging.

Triacetone triperoxide (TATP) and its byproduct diacetone diperoxide (DADP) are commonly used home-made high explosives in bombing cases and terrorist attacks. However, these two peroxide explosives are unstable and prone to thermal decomposition, leading to challenges in sample collection and preparation in bombing cases. Therefore, there is an urgent need to develop an in situ identification method for TATP and DADP. Compared to the solvent-based swabbing methods commonly used for trace explosive collection, the tape lifting method can collect explosive particles and other potential evidence without damaging fingerprints or DNA. This study aims to develop a tape lifting method to collect trace explosive particles in bombing cases and an in situ method to identify TATP and DADP particles on the sticky side of transparent tape directly using laser confocal Raman spectroscopy. One type of fingerprint tape and two types of office tape were used to collect peroxide explosive particles followed by particle fixation on glass slides. Laser confocal Raman spectroscopy was applied to directly identify target particles, without peeling the attached tape off the glass slide. A solid-state laser emitting at 473 nm was suitable for Raman and imaging analysis of TATP and DADP. To mimic the real situation, the synthetic TATP and DADP were passed through a 100-mesh sieve, respectively. Fifty µg of each explosive powder was weighed, mixed and spread on a wooden table with dust in an area of 10 × 10 cm2. Subsequently, the samples were collected with the fingerprint tape. A targeted area of the tape with suspicious particles was imaged for analysis. Based on the difference between the characteristic Raman bands of TATP and DADP, the band ranges of 530-550 cm-1 and 750-770 cm-1 were selected, respectively, for obtaining the distribution information. The combination of Raman technology and the tape lifting method shows great potential for in situ identification of forensic samples by providing chemical and spatial information.

[Recent advances in stable isotope ratio analysis of common explosives].

The ratio of stable isotopes of the elements in explosives differs depending on the raw materials obtained from different geographical sources or the production processes adopted. Hence, this ratio can be used as an important index for the comparison and trace of explosives. Isotope ratio mass spectrometry (IRMS), a high-precision method for the analysis of stable isotope ratios, has evolved into a mature tool in this regard. In combination with elemental analysis, gas chromatography, liquid chromatography, etc., IRMS is widely used in food safety, environmental protection, forensic science, and other fields. IRMS also plays an important role in the comparison and trace of explosives. Since its application to distinguish trinitrotoluene (TNT) produced in different countries in 1975, IRMS has been successfully used in the analysis of various explosives. However, there is no systematic summary on the research progress on the stable isotope ratio analysis of common explosives. This paper provides a brief description of the related principle, instrumental composition, and characteristics of stable isotope ratio analysis. Methods for the stable isotope ratio analysis of common explosives such as ammonium nitrate, black powder, TNT, pentaerythritol tetranitrate (PETN), and cyclotrimethylene trinitroamine (RDX) are reviewed. The bulk stable isotopic ratio analysis method was used in most of the studies to determine the total isotope ratio of the sample. A compound-specific isotope analysis method was also employed to determine the isotope ratio of organic explosives in a complex matrix. The reported stable isotope ratios of explosives such as ammonium nitrate, black powder, and TNT produced in different countries are summarized. The discrimination ability of the stable isotope ratio for explosives is discussed. Based on the stable isotope ratio, explosives from different sources can be distinguished effectively. By combining the results of elemental analysis with the ICP-MS results, the discrimination efficiency of different samples could be further improved. The influence of relevant factors on the isotope ratio during the production and storage of explosives are collated. There is a strong correlation between the stable isotope ratios of explosives and raw materials. The stable isotope ratios of TNT, PETN, and other explosives are related to that of nitric acid used in the production. The stable isotope ratios of nitrogen and oxygen in the explosive are relatively stable and almost unchanged within one year of production. The complexity of the environmental matrix at the explosion site and the low concentration of explosive residues make the stable isotope analysis of explosive residues challenging. However, the changes in the stable isotope ratio before and after the explosion are discussed. Since there is no information on the application of stable isotope analysis to the traceability of explosives, the paper mentions that the standardized explosive sample pretreatment, stable isotope analysis method, collection and analysis of large amounts of explosive samples, and explosive stable isotope database are the basis of explosive traceability. This paper also outlines the existing challenges in the analysis of the stable isotope ratios of explosives, including the small number of explosive samples, lack of a stable isotope explosive analysis database, and difficulty in the stable isotope analysis of explosive residues. Possible solutions to these problems are proposed, followed by suggestions for the future development of the stable isotope ratio analysis of common explosives. The suggestions include establishing an effective extraction and enrichment method for explosive residues, combining IRMS with GC or LC for analyzing explosives, establishing a comprehensive process for the analysis of the stable isotope ratios of inorganic and organic explosives, and comparison and analysis of the stable isotope analysis data using statistical methods.

Detection of latent fingerprint hidden beneath adhesive tape by optical coherence tomography.

Adhesive tape is one type of common item which can be encountered in criminal cases involving rape, murder, kidnapping and explosives. It is often the case that a suspect deposits latent fingerprints on the sticky side of adhesive tape material when tying up victims, manufacturing improvised explosive devices or packaging illegal goods. However, the adhesive tapes found at crime scenes are usually stuck together or attached to a certain substrate, and thus the latent fingerprints may be hidden beneath the tapes. Current methods to detect latent fingerprint hidden beneath adhesive tape need to peel it off first and then apply physical or chemical methods to develop the fingerprint, which undergo complicated procedures and would affect the original condition of latent print. Optical coherence tomography (OCT) is a novel applied techniques in forensics which enables obtaining cross-sectional structure with the advantages of non-invasive, in-situ, high resolution and high speed. In this paper, a custom-built spectral-domain OCT (SD-OCT) system with a hand-held probe was employed to detect fingerprints hidden beneath different types of adhesive tapes. Three-dimensional (3D) OCT reconstructions were performed and the en face images were presented to reveal the hidden fingerprints. The results demonstrate that OCT is a promising tool for rapidly detecting and recovering high quality image of latent fingerprint hidden beneath adhesive tape without any changes to the original state and preserve the integrity of the evidence.

Characterization of automotive paint by optical coherence tomography.

Automotive paint is common trace evidence that plays a significant role in many vehicle-related criminal cases. However, the conventional methods of obtaining tomographic images tend to damage the samples. Optical coherence tomography (OCT) is a novel method to obtain high-resolution and cross-sectional images of the automotive paints in a non-destructive, and high-speed manner. In this study, OCT was applied to image and analyze the automotive paint, using scanning electron microscope (SEM) as reference. Eight automotive paint samples of different brands were examined. The images of multi-layer structures provided by OCT system with 5µm depth resolution were consistent with those by SEM. To distinguish different paints with similar visual appearance, we extracted internal structural features from the images using peak analysis and optical attenuation fit. Six characterized parameters were found to distinguish the samples including the optical path length (OPL) of base coat, the optical attenuation coefficient (OAC) of base coat, the OPL of clear coat, the back-scattering ratio (BSR) of clear coat and base coat, the OPL of primer surfacer, and the BSR of base coat and primer. Statistical differences were evaluated by an independent t-test with p<0.05. OCT was applied to analyze repainted paint as well. Three-dimensional OCT reconstruction of the paints was also implemented to create en face (transverse section) images for morphology examination and comparison. These results suggest that OCT imaging can provide additional new features for analyzing the automotive paints and thereby may be a promising supplement to traditional methods. Meanwhile, the OCT system is favorable for achieving in-situ and real-time examination at the scene of crime.

Elemental analysis of white electrical tapes by wavelength dispersive X-ray fluorescence spectrometry.

The aim of this study was to analyze and discriminate electrical tapes using the wavelength dispersive X-ray fluorescence (XRF) spectrometry and statistical techniques. The backings of 46 white electrical tapes were analyzed. A discrimination of 90.4% was performed only by quantitative analysis of major elements (relative ratio of Cl to Ca). Ten distinct groups with a discrimination of 78.9% were yielded only by qualitative analysis of trace elements. Ninety-nine electrical tape pairs which could not be discriminated by major elements were further compared with the characteristics of trace elements. The overall discriminating power of 96.1% was obtained by the combination of quantitative and qualitative analysis. The ability of XRF technique to discriminate different electrical tapes was similar to several well-known methods combined.

Lyotropic liquid crystalline phases formed in an ionic liquid.

Lyotropic liquid crystalline phases of an amphiphilic block copolymer are constructed and characterized in an ionic liquid with comparison of component and temperature effects.