Analysis of different materials subjected to open-air explosions in search of explosive traces by Raman microscopy

Post-explosion scenes offer such chaos and destruction that evidence recovery and detection of post-blast residues from the explosive in the surrounding materials is highly challenging and difficult. The suitability of materials to retain explosives residues and their subsequent analysis has been scarcely investigated. Particularly, the use of explosive mixtures containing inorganic oxidizing salts to make improvised explosive devices (IEDs) is a current security concern due to their wide availability and lax control. In this work, a wide variety of materials such as glass, steel, plywood, plastic bag, brick, cardboard or cotton subjected to open-air explosions were examined using confocal Raman microscopy, aiming to detect the inorganic oxidizing salts contained in explosives as black powder, chloratite, dynamite, ammonium nitrate fuel oil and ammonal. Post-blast residues were detected through microscopic examination of materials surfaces. In general, the more homogeneous and smoother the surface was, the less difficulties and better results in terms of identification were obtained. However, those highly irregular surfaces were the most unsuitable collectors for the posterior identification of explosive traces by Raman microscopy. The findings, difficulties and some recommendations related to the identification of post-blast particles in the different materials studied are thoroughly discussed

The discrimination of 72 nitrate, chlorate and perchlorate salts using IR and Raman spectroscopy

Inorganic oxidizing energetic salts including nitrates, chloratesand perchlorates are widely used in the manufacture of not only licit pyrotechnic compositions, but also illicit homemade explosive mixtures. Their identification in forensic laboratories is usually accomplished by either capillary electrophoresis or ion chromatography, with the disadvantage of dissociating the salt into its ions. On the contrary, vibrational spectroscopy, including IR and Raman, enables the non-invasive identification of the salt, i.e. avoiding its dissociation. This study focuses on the discrimination of all nitrate, chlorate and perchlorate salts that are commercially available, using both Raman and IR spectroscopy, with the aim of testing whether every salt can be unequivocally identified. Besides the visual spectra comparison by assigning every band with the corresponding molecular vibrational mode, a statistical analysis based on Pearson correlation was performed to ensure an objective identification, either using Raman, IR or both. Positively, 25 salts (out of 72) were unequivocally identified using Raman, 30 salts when using IR and 44 when combining both techniques. Negatively, some salts were undistinguishable even using both techniques demonstrating there are some salts that provide very similar Raman and IR spectra

Chemical classification of explosives

This work comprehensively reviews some fundamental concepts about explosives and their two commonly used classifications based on either their velocity of detonation or their application. These classifications are highly useful in the military/legal field, but completely useless for the chemical determination of explosives. Because of this reason, a classification of explosives based on their chemical composition is comprehensively revised, discussed and updated. This classification seeks to merge those dispersed chemical classifications of explosives found in literature into a unique general classification, which might be useful for every researcher dealing with the analytical chemical identification of explosives. In the knowledge of the chemical composition of explosives, the most adequate analytical techniques to determine them are finally discussed

Detection and identification of explosives by surface enhanced Raman scattering

Surface Enhanced Raman Scattering (SERS) has undergone an important development over the last few years, particularly in the detection and identification of extremely low traces of explosives. The large number of studies and results generated by this increasing research makes a comprehensive overview necessary. This work reviews in detail that research focused on the identification of explosives by SERS, including TNT, DNT, RDX, PETN, TATP, HMTD, perchlorate, etc. either in bulk state, in solution or in vapour phase. In brief, TNT and DNT have been widely studied by SERS due to its aromatic structure and LODs down to 5&#-10 zg and 10-17&-10-13 M have been achieved. The other explosives have been quite less researched; therefore, few results are available to be compared and a bit more modest LODs have been reached such as 10-13 M for RDX, 10‑4 M for TATP, 5 pg for PETN, or 10-9 M for perchlorate. In addition, the challenges of detecting both explosives vapours and perchlorate anion by SERS are thoroughly discussed.Prevention of and Fight against Crime Programme European Commission - Directorate-General Home Affair

Interpreting the near infrared region of explosives

The NIR spectra from 1000 to 2500 nm of 18 different explosives, propellant powders and energetic salts were collected and interpreted. NIR spectroscopy is known to provide information about the combination bands and overtones of highly anharmonic vibrations as those occurring in XH bonds (CH, NH and OH). Particularly intense and complex were the bands corresponding to the first combination region (2500&#-1900&;8239#nm) and first overtone stretching mode (2nu) of CH and NH bonds (1750&#-1450&;8239#nm). Inorganic oxidizing salts including sodium/potassium nitrate, sodium/potassium chlorate, and sodium/potassium perchlorate displayed low intense or no NIR bands

Detection of microscopic traces of explosive residues on textile fabrics by Raman spectroscopy

Direct or cross‐contamination of explosive residues on clothing is of high occurrence when handling explosive materials, leading to physically trapped particles between the fibres. In this work, the detection and identification of trace amounts of organic explosives, inorganic explosives, and oxidizing salts trapped between the fibres of dyed and undyed synthetic and natural textile clothing fabrics were studied using two (desktop and portable) confocal Raman microscopes. The results show that, despite the contribution of the textile fabric in terms of fluorescence and vibrational bands coming from the fibres and dyes, detection and identification of the explosive/oxidizing salt particles trapped on highly interfering surfaces was possible. Limits of detection were estimated in the nanogram/picogram range depending on the explosive and fabric. However, problems involving the burning of either some explosive particles or dark cloth textiles were verified, which can cause a destruction of the sample. Also, the analysis of improvised homemade explosives (potassium nitrate mixed with 10 different fuel substances) was studied to evaluate possible interferences

Simple multispectral imaging approach for determining the transfer of explosive residues in consecutive fingerprints

This novel investigation focused on studying the transfer of explosive residues (TNT, HMTD, PETN, ANFO, dynamite, black powder, NH4NO3, KNO3, NaClO3) in ten consecutive fingerprints to two different surfaces &- cotton fabric and polycarbonate plastic &- by using multispectral imaging (MSI). Imaging was performed employing a reflex camera in a purpose-built photo studio. Images were processed in MATLAB to select the most discriminating frame &- the one that provided the sharpest contrast between the explosive and the material in the red-green-blue (RGB) visible region. The amount of explosive residues transferred in each fingerprint was determined as the number of pixels containing explosive particles. First, the pattern of PETN transfer by ten different persons in successive fingerprints was studied. No significant differences in the pattern of transfer of PETN between subjects were observed, which was also confirmed by multivariate analysis of variance (MANOVA). Then, the transfer of traces of the nine above explosives in ten consecutive fingerprints to cotton fabric and polycarbonate plastic was investigated. The obtained results demonstrated that the amount of explosive residues deposited on successive fingerprints tended to undergo a power or exponential decrease, with the exception of inorganic salts (NH4NO3, KNO3, NaClO3) and ANFO (consists of 90% NH4NO3)

Study of the adhesion of explosive residues to the finger and transfer to clothing and luggage

It is important to understand the extent of transfer of explosive particles to different surfaces in order to better evaluate potential cross-contamination by explosives in crowded security controls such as those at airports. This work investigated the transfer of nine explosive residues (ANFO, dynamite, black powder, TNT, HMTD, PETN, NH4NO3, KNO3, NaClO3) through fingerprints from one surface to another. First, the extent of adhesion of explosive residues from different surfaces to the bare finger, nitrile and latex gloves was studied. Then, the transfer of explosive residues from one surface to another through fingerprints was investigated. Cotton fabric (hereinafter referred to as cotton) as clothing material and polycarbonate plastic (hereinafter referred to as polycarbonate) as luggage material were chosen for the experiments. These surfaces containing explosive particles were imaged using a reflex camera before and after the particles were transferred. Afterwards the images were processed in MATLAB where pixels corresponding to explosive residues were quantified. Results demonstrated that transfer of explosive residues frequently occurred with certain differences among materials. Generally, the amount of explosive particles adhered to the finger decreased in the following order: skin>latex>nitrile, while the transfer of particles from the finger to another surface was the opposite. The adhesion of explosive residues from polycarbonate to the finger was found to be better compared to cotton, while the amount of particles transferred to cotton was higher

Chemical classification of new psychoactive substances (NPS)

This work comprehensively reviews some fundamental concepts about drugs, especially focusing on new psychoactive substances (NPS), and their typical classifications based on either their effects (hallucinogens, stimulants or depressants), their origin (natural, synthetic, or semisynthetic), or legal situation (lawful, illicit, or unregulated). These classifications are highly useful in the medicine/legal field, but completely useless for the chemical determination of drugs. Hence, a classification of NPS based on their chemical composition is revised and discussed. This classification seeks to merge those recent and dispersed chemical groupings of NPS found in scientific literature and/or health/drugs reports from World/European/American Institutions facing the illicit use of drugs (WHO, UNODC, EMCDDA, OEDA, DEA, etc.) into a unique general classification, which might be useful for every forensic practitioner/researcher dealing with the identification of new psychoactive substances

Differentiation of body fluid stains on fabrics using external reflection Fourier transform infrared spectroscopy (FTIR) and chemometrics

Body fluids are evidence of great forensic interest due to the DNA extracted from them, which allows genetic identification of people. This study focuses on the discrimination among semen, vaginal fluid and urine stains (main fluids in sexual crimes) placed on different coloured cotton fabrics by external reflection FTIR spectroscopy combined with chemometrics. Semen-vaginal fluid mixtures and potential false positive substances commonly found in daily life such as soaps, milk, juices and lotions were also studied. Results demonstrated that the IR spectral signature obtained for each body fluid allowed its identification and the correct classification of unknown stains by means of Principal Components Analysis (PCA) and Soft Independent Modelling of Class Analogy (SIMCA). Interestingly, results proved that these IR spectra did not show any bands due to the colour of the fabric and no substance of those present in daily life which were analysed, provided a false positive