Ma Ángeles Fernández de la Ossa

Detection of residues from explosive manipulation by near infrared hyperspectral imaging: a promising forensic tool.

In this study near infrared hyperspectral imaging (NIR-HSI) is used to provide a fast, non-contact, non-invasive and non-destructive method for the analysis of explosive residues on human handprints. Volunteers manipulated individually each of these explosives and after deposited their handprints on plastic sheets. For this purpose, classical explosives, potentially used as part of improvised explosive devices (IEDs) as ammonium nitrate, blackpowder, single- and double-base smokeless gunpowders and dynamite were studied. A partial-least squares discriminant analysis (PLS-DA) model was built to detect and classify the presence of explosive residues in handprints. High levels of sensitivity and specificity for the PLS-DA classification model created to identify ammonium nitrate, blackpowder, single- and double-base smokeless gunpowders and dynamite residues were obtained, allowing the development of a preliminary library and facilitating the direct and in situ detection of explosives by NIR-HSI. Consequently, this technique is showed as a promising forensic tool for the detection of explosive residues and other related samples.

Determination of nitrocellulose by capillary electrophoresis with laser-induced fluorescence detection

The industrial application of nitrocellulose depends on its nitrogen content. When nitrocellulose presents high nitrogen content is used in the manufacture of explosives whereas nitrocellulose with low nitrogen content is used to make a wide range of daily and non-explosive products (e.g. cigarettes, paints, lacquers). This fact makes really important to develop a method for the determination and discrimination of nitrocellulose samples. This work reports, for the first time, the qualitative determination of nitrocellulose previously derivatized with 8-aminopyrene-1,3,6-trisulfonic acid (APTS) by capillary electrophoresis (CE-LIF) with laser-induced fluorescence detection (CE-LIF). APTS-labeled nitrocellulose was determined in lowly and highly nitrated nitrocellulose samples present in collodions and smokeless gunpowders, respectively, after their pulverization in liquid nitrogen. The method described enables the visual discrimination of different nitrocelluloses on the basis of the different electrophoretic profiles obtained, and provides a useful tool to determine nitrocellulose. Additionally, the use of field-amplified sample injection (FASI) enabled enhanced sample detection, which made it possible to determine nitrocellulose contained in ∼15 μg of gunpowder.

Near infrared spectral imaging for the analysis of dynamite residues on human handprints.

This study examines the utility of near infrared hyperspectral imaging (NIR-HSI) combined with chemometrics for the detection of dynamite residues on human handprints. Polyvinyl sheets containing dynamite residues were then analysed with the NIR-HSI system. A spectral library was developed by using partial least squares-discriminant analysis model (PLS-DA) to detect and classify the pixels contaminated with the dynamite residues. Values of sensitivity and specificity of 100% were obtained for both calibration and cross validation of dynamite and ammonium nitrate. The results were tested in real human handprints. Seven volunteers deposited their handprints into polyvinyl transparent sheets after the manipulation of a common type of dynamite which was mainly composed by ammonium nitrate. These results highlight the extremely high potential and capability of NIR-HSI combined with chemometrics for the fast and easy identification of explosive residues and additionally, its potential competence to detect the explosive manipulation.

Discrimination of non-explosive and explosive samples through nitrocellulose fingerprints obtained by capillary electrophoresis.

This work is focused on a novel procedure to discriminate nitrocellulose-based samples with non-explosive and explosive properties. The nitrocellulose study has been scarcely approached in the literature due to its special polymeric properties such as its high molar mass and complex chemical and structural characteristics. These properties require the nitrocellulose analysis to be performed by using a few organic solvents and in consequence, they limit the number of adequate analytical techniques for its study. In terms of identification of pre-blast explosives, mass spectrometry is one of the most preferred technique because it allows to obtain structural information. However, it has never been used to analyze polymeric nitrocellulose. In this study, the differentiation of non-explosive and explosive samples through nitrocellulose fingerprints obtained by capillary electrophoresis was investigated. A batch of 30 different smokeless gunpowders and 23 different everyday products were pulverized, derivatized with a fluorescent agent and analyzed by capillary electrophoresis with laser-induced fluorescence detection. Since this methodology is specific to d-glucopyranose derivatives (cellulosic and related compounds), and paper samples could be easily found in explosion scenes, 11 different paper samples were also included in the study as potential interference samples. In order to discriminate among samples, multivariate analysis (principal component analysis and soft independent modeling of class analogy) was applied to the obtained electrophoretic profiles. To the best of our knowledge, this represents the first study that achieve a successful discrimination between non-explosive and explosive nitrocellulose-based samples, as well as potential cellulose interference samples, and posterior classification of unknown samples into their corresponding groups using CE-LIF and chemometric tools.

Progressing the analysis of Improvised Explosive Devices: Comparative study for trace detection of explosive residues in handprints by Raman spectroscopy and liquid chromatography

Concerning the dreadful global threat of terrorist attacks, the detection of explosive residues in biological traces and marks is a current need in both forensics and homeland security. This study examines the potential of Raman microscopy in comparison to liquid chromatography (ion chromatography (IC) and reversed-phase high performance liquid chromatography (RP-HPLC)) to detect, identify and quantify residues in human handmarks of explosives and energetic salts commonly used to manufacture Improvised Explosive Devices (IEDs) including dynamite, ammonium nitrate, single- and double-smokeless gunpowders and black powder. Dynamite, ammonium nitrate and black powder were detected through the identification of the energetic salts by Raman spectroscopy, their respective anions by IC, and organic components by RP-HPLC. Smokeless gunpowders were not detected, either by Raman spectroscopy or the two liquid chromatography techniques. Several aspects of handprint collection, sample treatment and a critical comparison of the identification of compounds by both techniques are discussed. Raman microscopy and liquid chromatography were shown to be complementary to one another offering more comprehensive information for trace explosives analysis.

Anions in pre‐ and post‐blast consumer fireworks by capillary electrophoresis

Consumer fireworks are a heterogeneous group of pyrotechnic items widely used by citizens around the world. There are a wide number of forensic cases related to consumer fireworks that require knowing their chemical composition and variety of designs to conduct accurate and comprehensive analyses. In this research paper, a selection of six consumer firework types (firecracker, rocket, pyrotechnic fountain, pyrotechnic battery, sparkler, and smoke bomb) is physically described and their anionic compositions are determined. Preblast (fuses and charges) samples and postblast residues of the different consumer fireworks were analyzed by CE in order to determine their anionic composition. Different types of chemical compositions in fuses and pyrotechnic charges were determined, although they were not related to any type of item. Additionally, several discrepancies were found between the analytical results and the declared item compositions. Regarding postblast residues, a huge variety of anions were identified and attributed to some unconsumed starting materials and different chemical reactions occurring during combustion.

Differentiation of Body Fluid Stains on Fabrics Using External Reflection Fourier Transform Infrared Spectroscopy (FT-IR) 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 colored cotton fabrics by external reflection Fourier transform infrared spectroscopy (FT-IR) 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 component analysis (PCA) and soft independent modeling of class analogy (SIMCA). Interestingly, results proved that these IR spectra did not show any bands due to the color of the fabric and no substance of those present in daily life which were analyzed, provided a false positive.

Near promising future of near infrared hyperspectral imaging in forensic sciences

uring the last decade, the ille-gal use of improvised explosive devices (IEDs) for non-civilian purposes has unfortunately increased worldwide. For example, the terrorist attacks in Madrid in 2004 or, more recently, in Boston in 2013, present a big concern in the international and homeland security communities. In this sense, large and combined efforts are being made by law enforcement, defence, forensic researchers and industry with the aim of developing effective technologies suitable for the analysis of explosives in real situations. These technologies are also required to be fast, non-contact, non-invasive and non-destructive in order to assure the safety of the analysts by achieving minimal or no interaction with these materials. Near infrared (NIR) hyperspectral imaging (HSI) presents an interesting possibility in this field. It is very well known that HSI-NIR integrates con-ventional NIR spectroscopy with surface scanning. This provides fast, non-con-tact, non-invasive and non-destructive measurements of the scanned surface and provides two different kinds of infor-mation: the spectral and spatial charac-teristics of the scanned surface. HSI-NIR is, therefore, very attractive and suitable for the detection and identification of energetic, and normally unstable, materi-als such as explosives, avoiding the man-datory sample treatments required in tra-ditional separation techniques which lead to potential risks to the analysts and the partial or total destruction of the sample.Examining existing bibliographies, infra-red spectroscopy has been widely used for explosive analysis including pre-blast samples and post-blast residue identifi-cation.

Analysis and differentiation of paper samples by capillary electrophoresis and multivariate analysis

This work reports an investigation for the analysis of different paper samples using CE with laser‐induced detection. Papers from four different manufactures (white‐copy paper) and four different paper sources (white and recycled‐copy papers, adhesive yellow paper notes and restaurant serviettes) were pulverized by scratching with a surgical scalpel prior to their derivatization with a fluorescent labeling agent, 8‐aminopyrene‐1,3,6‐trisulfonic acid. Methodological conditions were evaluated, specifically the derivatization conditions with the aim to achieve the best S/N signals and the separation conditions in order to obtain optimum values of sensitivity and reproducibility. The best conditions, in terms of fastest, and easiest sample preparation procedure, minimal sample consumption, as well as the use of the simplest and fastest CE‐procedure for obtaining the best analytical parameters, were applied to the analysis of the different paper samples. The registered electropherograms were pretreated (normalized and aligned) and subjected to multivariate analysis (principal component analysis). A successful discrimination among paper samples without entanglements was achieved. To the best of our knowledge, this work presents the first approach to achieve a successful differentiation among visually similar white‐copy paper samples produced by different manufactures and paper from different paper sources through their direct analysis by CE‐LIF and subsequent comparative study of the complete cellulose electropherogram by chemometric tools.