Ivana Turková

Analysis of nonstandard and home-made explosives and post-blast residues in forensic practice

Nonstandard and home-made explosives may constitute a considerable threat and as well as a potential material for terrorist activities. Mobile analytical devices, particularly Raman, or also FTIR spectrometers are used for the initial detection. Various sorts of phlegmatizers (moderants) to decrease sensitivity of explosives were tested, some kinds of low viscosity lubricants yielded very good results. If the character of the substance allows it, phlegmatized samples are taken in the amount of approx.0.3g for a laboratory analysis. Various separation methods and methods of concentrations of samples from post-blast scenes were tested. A wide range of methods is used for the laboratory analysis. XRD techniques capable of a direct phase identification of the crystalline substance, namely in mixtures, have highly proved themselves in practice for inorganic and organic phases. SEM-EDS/WDS methods are standardly employed for the inorganic phase. In analysing post-blast residues, there are very important techniques allowing analysis at the level of separate particles, not the overall composition in a mixed sample.

Identification of improvised explosives residues using physical-chemical analytical methods under real conditions after an explosion

Within the analysis of cases relating to the use of explosives for crimes, we have experienced a shift from using industrial explosives towards substances made in amateur and illegal way. Availability of industrial explosives is increasingly limited to a narrow sphere of subjects with a relevant permission. Thus, on the part of perpetrators, terrorists, ever greater attention is paid to illegal production of explosives that are easily made from readily available raw materials. Another alarming fact is the availability of information found on the internet. Procedures of preparation are often very simple and do not require even a deeper professional knowledge. Explosive characteristics are not actually accessible for many of these substances (detonation velocity, sensitivity, working capacity, brisance, physical and chemical stability, etc.). Therefore, a project is being implemented, which on grounds of assessment of individual information available in literature and on the internet, aiming at choosing individual areas of potentially abusable substances (e.g. mixtures of nitric acid (98%) with organic substances, mixtures nitromethane and tetranitromethane with organic substances, mixtures of chlorates and perchlorates of alkali metals with organic substances, chemically individual compounds of organic base type of perchloric acid, azides, fulminates, acetylides, picrates, styphnates of heavy metals, etc.). It is directed towards preparation of these explosives also in non-stoichiometric mixtures, conducting test explosives, determination of explosive characteristics (if they are unknown) and analysis of both primary phases and post-blast residues through available analytical techniques, such as gas and liquid chromatography with mass detection, FTIR, micro-Raman spectrometry, electron microscopy with microanalysis and Raman microspectrometry directly in SEM chamber for analysis at the level of individual microparticles. The received characteristics will be used to extend knowledge database for security forces.

New possibilities to analyse non-standard explosives and post blast residues in forensic practice

Nonstandard and home-made explosives always pose a considerable threat for security forces in terms of their practically unlimited variability, both in composition and in construction of explosive devises. Electron microscopy – SEM with EDS/WDS is one of the key techniques for an analysis of non-standard explosives and post-blast residues. If the amount of materials allows it, a number of other analytical techniques are utilized, such as XRD that is capable of a direct phase identification of a crystalline substance, namely in mixtures. TLC has constantly proved itself useful for laboratory screening. Furthermore, combinations of FTIR, Raman spectrometry, LC MS, GC MS, XRF, micro XRF and other ones are applied. In the case of identification of post-blast residues, where an investigation is often conducted at the level of separate microscopic particles, the role of SEM is unsubstitutable, whereas the analysis of the organic phase from these often sporadic microparticles has been infeasible until recently. One of the very interesting options appears to be Raman spectrometry technique, which is nowadays obtainable as a supplement to SEM EDX. Newly available is the device that is fully confocal, SEM keeps full functionality and scan range, very high resolution (for green laser resolution 360nm FWHM; 430nm Rayleigh), it is fitted with high quality objective lens, enhances mapping through Raman spectrometry in a volume 250μm x 250μm x 250μm by piezo driven scanner (capacitive feedback linearized) and obtaining a high quality white light image (250μm x 250μm) immediately in the SEM chamber. This technique is currently undergoing intensive testing and it seems that the method could significantly help to address issues with the analysis of organic phases in electron microscopy not only in the case of post-blast residues and explosives.

Electron microscopy and forensic practice

Electron microanalysis in forensic practice ranks among basic applications used in investigation of traces (latents, stains, etc.) from crime scenes. Applying electron microscope allows for rapid screening and receiving initial information for a wide range of traces. SEM with EDS/WDS makes it possible to observe topography surface and morphology samples and examination of chemical components. Physical laboratory of the Institute of Criminalistics Prague use SEM especially for examination of inorganic samples, rarely for biology and other material. Recently, possibilities of electron microscopy have been extended considerably using dual systems with focused ion beam. These systems are applied mainly in study of inner micro and nanoparticles , thin layers (intersecting lines in graphical forensic examinations, analysis of layers of functional glass, etc.), study of alloys microdefects, creating 3D particles and aggregates models, etc. Automated mineralogical analyses are a great asset to analysis of mineral phases, particularly soils, similarly it holds for cathode luminescence, predominantly colour one and precise quantitative measurement of their spectral characteristics. Among latest innovations that are becoming to appear also at ordinary laboratories are TOF - SIMS systems and micro Raman spectroscopy with a resolution comparable to EDS/WDS analysis (capable of achieving similar level as through EDS/WDS analysis).

Application possibilities of several modern methods of microscopy and microanalysis in forensic science field

The methods of optical and electron microscopy and microanalysis are the linchpin of forensic inorganic analysis. However, their capacity is limited as for the exact identification of pigments and colour layers, and therefore it is essential that they be complemented by other methods of phase microanalysis - powder X-ray microdiffraction (micro pXRD) and FTIR in transmission mode. The classic way of sample division for different methods is not suitable with regard to the inhomogeneity of the sequence of strata. That is why a method was tested that would allow performance of optical microscopy, SEM/EDS(WDS), micro pXRD and FTIR in a nondestructive manner, from an identical spot of a single fragment. The solution can be polished sections - embedded samples and microtome sections. Conductive zerobackground single-crystal silicon plates were developed and tested for sample fixation in SEM, micro pXRD and transmission FTIR. Methods using a focused ion beam - FIB have recently gained importance in the field of electron microscopy. In the forensic sphere they can be employed in examinations of metal materials, technical analyses of documents, post-blast and gunshot residues.

GSR particles and their evidential value

Analysis of gunshot residues (GSR) is one of major areas in microparticle investigation. Results of the analysis usually have a high evidential value, but some information about potential secondary contamination by GSR is needed to maintain its value. A three-year study was carried out for ascertaining the level of possible secondary contamination monitoring GSR particles in urban means of transports in Prague (underground, trams, busses), taxi cars, randomly chosen civil vehicles, vehicles and trains of suburban transport, at places with a high concentration of people (supermarkets, hypermarkets, banks and financial institutions, premises of post offices). We also performed sampling at premises of the Institute of Criminalistics Prague (common areas, corridors, laboratory rooms), at police stations and in patrol cars of the Police of the Czech Republic, including Prague Metropolitan Police. Next, persons form selected professional groups of inhabitants (policemen, car mechanics, civilians without contact with a firearm and people who are in contact with hunting weapons - huntsmen and gamekeepers) were sampled as well.

Forensic database of homemade and nonstandard explosives

Analysis of homemade and nonstandard explosives and their post-blast residues may be a bit of a challenge for forensic analysis. Analysis of these materials becomes more and more important concerning both the current global situation and the considerably easy access to precursors that are often commonly obtainable chemicals. The aim of two year running project is prepare some of these substances and carry out experimental explosions and tests, and map analyses possibilities using a wide range of available analytical techniques in forensic labs. Samples of primary substances, prepared explosives and post-blast residues are analysed in a complex way in terms of organic and inorganic components. All data obtained, including visual documentation, are stored in a specialized database for security forces and their expert workplaces. The first version of the database is to be introduced.

Methods for characterization of home-made and non-standard explosives in forensic science (Conference Presentation)

Availability of industrial explosives is increasingly limited. Thus, on the part of perpetrators, terrorists, ever greater attention is paid to illegal productions that are easily made from readily available raw materials. Alarming fact is the availability of information found on the internet. In the forensic field are often faced with the problem of analysis of tiny remnants post-blast residues. Residues are analysed comprehensively both in terms of organic and inorganic contents. Organic analysis - the use of the two-stage instrumental sequence in the order - primary instrumental separation technique and secondary sensitive analytical detection. As separation techniques will be applied methods of gas and liquid chromatography. Gas chromatography (GC) is used particularly to analyse volatile residues of explosives having a relatively high tension of vapours, characterized by a relatively high thermal stability (GC-MSD, GC-ECD). The technique of scanning electron microscopy in connection with EDS/WDS/microXRF analysis is employed to analyse samples containing inorganic components, the method allows not only a fundamental microanalysis of particles caught on the surfaces of the reference materials after explosions, but especially their distinction from ballast particles arising from contaminants occurring in the vicinity of the explosion. There are currently devices facilitating Confocal Raman Imaging from microparticles, or their sections directly in the SEM chamber or SEM/FIB dual systems. The new data from ongoing project “Identification of improvised explosives residues using physical-chemical analytical methods under real conditions after an explosion” will be presented.

Forensic practice in the field of protection of cultural heritage

Microscopic methods play a key role in issues covering analyses of objects of art that are used on the one hand as screening ones, on the other hand they can lead to obtaining data relevant for completion of expertise. Analyses of artworks, gemmological objects and other highly valuable commodities usually do not rank among routine ones, but every analysis is specific, be it e.g. material investigation of artworks, historical textile materials and other antiques (coins, etc.), identification of fragments (from transporters, storage places, etc.), period statues, sculptures compared to originals, analyses of gems and jewellery, etc. A number of analytical techniques may be employed: optical microscopy in transmitted and reflected light, polarization and fluorescence in visible, UV and IR radiation; image analysis, quantitative microspectrophotometry; SEM/EDS/WDS; FTIR and Raman spectroscopy; XRF and microXRF, including mobile one; XRD and microXRD; x-ray backlight or LA-ICP-MS, SIMS, PIXE; further methods of organic analysis are also utilised - GS-MS, MALDI-TOF, etc.