From forensic chemistry: an educational experience

3.1 Contents Unit 1

Unit 1: Scientific method in forensic investigation. Precision, accuracy, reproducibility, calibrations, use of standards, validation of techniques, figures of merit. Introduction to quality standards in laboratories in terms of safety, sample taking, chain of custody, qualified personnel, etc. ISO 17025, ISO 17020 and ILAC G19.

In Unit 1, we delve into the evolution portrayed in literature and mystery films. We explore how protagonists have transitioned from being brilliant investigators driven by instinct and sagacity, seeking clues and extracting confessions from the guilty, as depicted in novels by Agatha Christie, to modern researchers who predominantly work in laboratories equipped with sophisticated technology. We draw upon the stories of Alexandre Lacassagne and Edmond Locard as examples of methodological scientific researchers. Present-day criminal investigations heavily rely on irrefutable scientific evidence, emphasizing the importance of meticulous work quality. This unit also introduces fundamental concepts such as laboratory quality standards, chain of custody protocols, and safety measures within laboratory settings. (Kanu et al., 2015) The interdisciplinary approach, even within the chemical laboratory, is another relevant point to emphasize with students. To illustrate these elements, we will examine various scientific cases that have garnered significant media attention. Given that some of these news stories may be controversial or biased due to editorial criteria, it is agreed with the students that the published information will be considered valid, and analyses will be conducted based on that data. This approach is designed to prevent discussions that might divert students from the core focus of the course.

We specifically address the following cases: As a preview of Unit 4, we examine the use of firearms, including the deaths of prosecutor Alberto Nisman (Argentina, 2015) and Carlos Menem Jr. (Argentina, 1995). In advance of Unit 5 we explore the explosion at the Río Tercero military factory (Argentina, 1995) and the attack on the AMIA (Argentina, 1994). Fast forward to Units 6 and 7 focusing on the destruction of chemical warfare agents (CWA) in Libya (Libya, 2016) and the Bhopal chemical accident (India, 1984).

Although each case will later be analysed within the framework of its respective unit, for this introductory stage, in the first two cases the importance of preserving the crime scene, sampling and maintaining the chain of custody of the samples is emphasized. We discuss with students how laboratory results can support different hypotheses such as suicide versus murder, or accident versus attack.

The Argentine justice system has already classified the aforementioned explosion cases as criminal, the first being a cover-up of illegal arms sales and the second a terrorist act. In this case, students are presented with the fundamental need to understand how explosions occur in order to look for analysable evidence.

In the last two cases, although one involves CWA, which may be unknown to students, we focus more on the risks associated with the transportation and storage of hazardous chemicals, particularly as environmental and public health hazards. The Bhopal incident constitutes an extreme example of an industrial accident and is an emblematic case for analysis.

Given the widespread impact of these cases, in this unit, videos and news reports are presented that allow each scenario to be recreated in the classroom. In this way, students participate as expert investigators, considering what evidence would be relevant in each case and preparing them for later units.

3.2 Contents Units 2, and 3

wUnit 2: Electromagnetic spectrum, signals from atoms and molecules. Relationship with different instrumental techniques (infrared and Raman spectrophotometry, electron microscopy, atomic absorption, ICP) – chromatography.

Unit 3: Extension of the analyses seen to other materials: cables, glass, fibres, tempering of marks and numbering, special papers and inks such as paper money, vehicle paints, particulate matter and soils.

In Unit 2, we focus mainly on instrumental analysis techniques, which are widely covered in the literature, such as the references cited in point 4 of this work. Unit 3 then presents some non-classical applications of these techniques.

A notable modification is the presentation of the instrumental techniques as a whole, allowing levels of detail to be adjusted to accommodate students without prior chemistry training, while maintaining rigor.

We begin by discussing the advantage of separating sample components for individual analysis, emphasizing the challenge posed by forensic samples, which may not always be available in sufficient quantities. The discussion begins with ink-on-paper chromatography, a technique feasible even in the classroom and particularly beneficial for non-chemistry students to visualize the operating principles. Later, gas and liquid chromatography (GC and HPLC) is introduced, along with the concept of specific detectors.

We then delve into the detectors, classifying them into spectroscopic and non-spectroscopic techniques, defining each one and briefly explaining their operating principles, applicable substance types, and considerations such as sensitivity, detection limits, specificity, interferences, false negatives, and false positives.

Under spectroscopic techniques, we cover atomic and molecular emission and absorption, line and band spectra, and related methods such as atomic absorption (AA), inductively coupled plasma (ICP) emission, infrared spectroscopy, Raman spectroscopy, and mass spectrometry. Non-spectroscopic techniques include transmission, refraction, reflection, polarization, diffraction, and scattering.

Finally, we discuss scanning electron microscopy (SEM) with X-ray fluorescence detection using energy and wavelength dispersion, due to its importance in certain forensic analyses.

Unit 3 provides examples of each technique with typical samples, demonstrating the results. Subsequent units will further explore these techniques and concepts in the context of specific types of crimes under study. This unit is primarily delivered through theoretical presentations and examples provided by the instructors in charge.

3.3 Contents Unit 4

Unit 4: Use of firearms, parts of ammunition. Deflagration and gunshot remains (gunpowder and primer). Chemical determinations aimed at determining the perpetrator of the shot, establishing the shooting distance and its trajectory, and establishing the weapon used. Sampling for different analysis techniques, common errors, contaminations.

Much of the work in a forensic laboratory is related to samples from events involving the use of firearms. This is undoubtedly a reason for its inclusion in this course, but from a chemical point of view, we can consider firearm ammunition as a basic model to understand the operation of explosive devices and even relate it to accidental explosions. With this objective, we will begin by identifying its elements, which in the next unit we will seek to identify in other scenarios. In this unit, videos are presented that illustrate the functioning of firearms, the components of ammunition, and the generation of gunshot residue (GSR), which will form the basis of the proposed analyses. The initiator, the explosive charge, the casing, and the projectile, along with their characteristics and composition, as well as their interaction with the scene, are central in this unit to answer the four most common questions: who fired the shot, from what distance, its trajectory, and what weapon was used.

So that these elements can be related, we begin by explaining how a firearm shot occurs. The need for a substance that is very sensitive to the impact of the firing pin opens the way to discussing the characteristics of initiators and their rapid ignition in response to physical stimuli. This will be exemplified with the use of mercury fulminate, lead azide, and lead trinitroresorcinate among the most common. The mention of the use of sodium azide in airbag devices indicates that there are more applications for these substances. But returning to the initiators, highlighting the presence of double and triple bonds with nitrogen in organometallic compounds or the presence of the nitro functional group in aromatics begins to stand out. This section is expanded by presenting the chemical structures of each compound, relating them to the operating principles of the instrumental techniques studied in the earlier units.

Given the nature of initiators and additive substances like barium nitrate and antimony sulfides, among the most common, to increase temperature and regulate combustion, the scanning electron microscopy (SEM) technique along with energy-dispersive X-ray spectroscopy (EDS) are recommended. SEM images allow identification of circular particles typically formed in high-temperature and pressure environments, while EDS helps establish their elemental composition, with Pb–Ba–Sb (lead, barium and antimony) being the most common currently. Other analysis alternatives, such as electrochemical determinations, are presented and discussed in class from the perspective of figures of merit (O’Mahony & Wang, 2013a).

The detonation of the initiator triggers the explosion of the charge, leading to increased pressure inside the casing, which is released upon ejection of the core or projectile. This segment introduces the characteristics of black powder and smokeless powder, their current uses, and presents nitrocellulose with additives as the foundation of explosive charges. The infrared and Raman spectra of nitrocellulose are analysed as methods for identifying gunpowder gunshot residues (GSR). The characteristic spectra that allow for the identification of these compounds are analysed with the students.

Although instrumental techniques offer excellent performance and are optimal for these types of samples, it is relevant to present the colorimetric techniques provided by qualitative analytical chemistry for these analytes and to compare the figures of merit within the context of forensic expertise.

3.4 Contents Unit 5

Unit 5: Classification of explosives: low, high, primary, and secondary. Military and industrial use. Detonation, explosion, and post-explosion and fire analysis. Search techniques and portable equipment. Expert technical report.

Although events involving fires or explosions are typically handled by firefighters, chemical laboratories can help provide answers about the origin of these incidents. Additionally, analysing the conditions that allow these incidents helps us evaluate how to avoid them in the activities we perform as chemists in laboratories and industries, which is the great challenge of working on these topics with students.

Firstly, we will state that oxidations, combustions, deflagrations, and detonations belong to the same group of chemical reactions where speed makes the difference. To understand what elements are necessary for their development, we present the fire triangle and tetrahedron with the key fire elements: fuel, oxidizer, activation energy, chain reaction. In this sense, the Navarra Fire Service in Spain, among others, has a large amount of material available (https://www.navarra.es/es/bomberos). Of course, we cannot talk about fire without discussing ignition points, inflammation, and auto-ignition, highlighting their relationship with the presence and persistence of a heat source as a critical part of these events.

From a forensic point of view, it is important to mention smoke analysis to determine the point of origin, as well as the study of the presence of accelerants (NFPA 921: Guide for the Investigation of Fires and Explosions/National Fire Protection Association). This topic allows us to introduce solid phase micro extraction (SPME) systems associated with gas chromatography with mass spectrometry detection (GC-MS) and the contribution of databases of materials and products marketed for the resolution of police cases.

Fires can be the initial stage that triggers an explosion or the final stage after it occurs, but the study of explosives goes beyond forensic analysis since it is carried out with other objectives, such as: characterization or remediation of contaminated sites, continuous measurement during manufacturing and storage (labour protection), demilitarization and removal of mines, and prevention of anti-terrorist activities. This is where we begin to relate this type of event with the degree of intentionality that it has and that in accidental events, prevention is directly related to the magnitude they can reach. Highlighting that when they occur in chemical establishments this is related to the security measures that are adopted.

For this, different cases are presented: Texas, USA 1947; Río Tercero, Argentina 1995; St. Petersburg, Russia 2017; Buenos Aires, Argentina 1994; Brussels, Belgium 2016. In all cases, the aim is to identify the elements of an explosion in relation to what is seen in ballistics: detonator, explosive charge, projectiles or fragments, container, and analyse which of these elements can be found in a post-explosion search. All cases are presented through original videos or news reports from the time they occurred, to place the student within the context of the event. At this stage, students, individually or in groups, propose hypotheses regarding the origin of the fire (listing the elements of the fire tetrahedron) or an explosion (identifying the initiator and explosive charge). From this global view of the subject, the classification of explosives is introduced according to Figure 1, but the relationship with the chemical structure is added according to whether they are organometallic compounds and organic peroxides, aliphatic and aromatic nitro compounds, and plastic explosives and ANFO (ammonium nitrate plus fuel oil) for primary, secondary, and tertiary explosives, respectively.

Figure 1:

Explosives classification.

Then we can link the classification elements of the explosive with its chemical structure or family of compounds and the instrumental techniques that allow its detection and analysis. This section is illustrated with different related scientific publications (Barron & Gilchrist, 2014; Bogue, 2015; Buryakov et al., 2014; Izake, 2010; López-López & García-Ruiz, 2014; Ma et al., 2015; Moore, 2004; O’Mahony & Wang, 2013b; Singh, 2007). For each case, students list the evidence or samples that can be analysed and suggest the appropriate instrumental techniques to be used in the laboratory, in relation to the chemical structure of these compounds.

In addition to training for the work of a forensic chemist, and given the occurrence of such events in chemistry laboratories, at the end of this unit, students discuss the importance of analysing the design of an experiment and detecting whether it contains elements and conditions that could potentially cause a fire or explosion. Students can describe experiments where high pressure or temperature conditions are generated, as well as the use of flammable substances, and collaboratively develop a list of suggested protective measures.

3.5 Contents Unit 6

Unit 6: Chemical weapons: identification of chemical agents. Classification, nervous and vesicant. Identification and analysis techniques. Convention on the Prohibition of the Development, Production, Stockpiling and Use of Chemical Weapons and on their Destruction. Dual use of chemicals – analysis of precursors linked to chemical activity.

This unit begins by reflecting on the impact of new scientific or technological knowledge or developments and provides a brief historical review, biased towards the chemical-biological component of their use in warfare (Spanevello & Suarez, 2011). From this introductory stage, we start defining concepts such as weapons of mass destruction, definition and classification, considering with students the infrastructure and impact related to each: nuclear, chemical, radiological, and biological. Other concepts to introduce for the future interpretation of regulations and conventions include disarmament, non-proliferation, and arms control. From this point, we will focus on the definition of a chemical weapon given in the Chemical Weapons Convention (CWC) to achieve a clear classification of them and distinguish them from the use of chemicals as weapons for their incendiary or explosive power, analysed in the previous unit. This is completed with the classification of chemical warfare agents (CWA) according to symptomatology or target organs: choking agents, blood agents, blister agents, and nerve agents, also mentioning incapacitating agents. Obviously, to reinforce the concept of a chemical weapon, we must analyse the stages of its production: precursors, synthesis, purification, storage, and distribution, considering the necessary equipment at each stage.

The presentation of the Battle of Ypres in 1915 and the role played by Fritz Haber marks a turning point in the large-scale use of chemical warfare agents and opens the discussion on the responsibility and ethics of scientific knowledge. This discussion is completed by analysing the actions of other scientists such as Francois Auguste Victor Grignard. For historical continuity, mentioning the background and the signing of the CWC itself is indispensable, emphasizing its four pillars: disarmament (Articles 3–5), non-proliferation (Article 6), assistance and protection (Article 10), and international cooperation (Article 11). With the destruction of the declared arsenal in September 2023, preventing re-emergence is a critical focus in the training of future generations of chemists. In line with United Nations Security Council Resolution 1540/2004, both terrorist acts and other activities not permitted by the convention related to the use of CWA can be mentioned, including new developments of nerve agents, which keeps this topic very current. In this context, the Organization for the Prohibition of Chemical Weapons (OPCW) and its role in implementing the CWC (https://www.opcw.org) are also presented. Beyond the international framework to raise awareness and focus the development of chemistry on peaceful uses, we are practically obliged to discuss dual-use. The lists used by the CWC and National Authorities of States Parties to ensure compliance with the law regarding the declaration of compounds controlled by these authorities will be presented (https://www.opcw.org/chemical-weapons-convention/annexes/annex-chemicals/annex-chemicals). After the theoretical presentation, enhanced with audiovisual material provided on the OPCW website, the course engages in a debate about the role of scientists in the development of CWAs and how to relate these positions to current ethical decisions, such as publishing controversial topics like synthesis routes for new toxic substances. Working with roles, taking on the perspectives of the scientific group, the editorial committee, or the ethics committee, proves to be highly enriching.

Returning to focus on the chemical nature of the compounds involved, we will relate each type of CWA with the common chemical structure of that family of compounds, especially in the cases of mustards and nerve agents, the latter group being organophosphates as the representative structure. This is essential both for their detection and for the design of their destruction (Dirección General de Armamento y Material. Subdirección General de Tecnología e Innovación, 2011; Kim et al., 2011; Vanninen, 2011). Regarding detection, the mentioned references provide different techniques and conditions, distinguishing which techniques meet the requirements for early warning, verification, and confirmation of the presence of CWA, allowing activation of international action provided in the CWC. As already analysed for explosives, techniques such as GC-MS, FTIR, and Raman Spectroscopy show adequate merit figures especially required for the confirmation of these compounds. Regarding their destruction, after disassembling the weapon, neutralization in an aqueous alkaline medium is carried out, followed by a bioremediation stage for mustards and supercritical oxidation for nerve agents. It should be noted that these methods replaced the incineration process, which was among the first to be used. This part of this unit begins to introduce the last unit of the course, related to the life and final fate of potentially dangerous compounds.

Having analysed compounds related to fires, explosions, and chemical weapons and becoming aware of the presence of such compounds in both academic laboratories and industrial plants on different scales, we are ready to think about chemical risk in its entirety. To this end, three cases of different nature and magnitude are analysed to highlight that the magnitude of an event is not necessarily determined by its intentionality and that lack of prevention can have consequences as severe as a deliberate act. The explosion in January 2010 at the University of Texas (USA), the explosion in December 2007 at the University of Río Cuarto (Argentina), and the explosion in August 2015 in Tianjin (China), the latter case already impacting the environment, as well as the explosion in Oppau (Germany) in 1921 or the chemical leak in Bhopal (India) in 1984 are studied. This type of analysis, although not related to CWA, allows us to introduce James Reason’s Swiss cheese model of accident causation and continue the discussion on ethics and responsibility in the professional practice of chemistry. The unit is crowned with the presentation of The Hague Ethical Guidelines (https://www.opcw.org/hague-ethical-guidelines), highlighting that the International Union of Pure and Applied Chemistry (IUPAC), the International Council of Chemical Associations (ICCA), and the International Chemical Trade Association (ICTA) have endorsed The Hague Ethical Guidelines to guide the responsible practice of chemistry under the norms of the Chemical Weapons Convention.

3.6 Contents Unit 7

Unit 7: Environmental crimes: Art. 41 of the National Constitution, Directive of the European Parliament P5_TA(2002)0147. Identification of activities that generate hazardous waste. Control of prevention, remediation and final disposal strategies for hazardous waste. Analysis techniques.

The classification of an act related to the environment as a crime will depend on the legislation of the place in question. In the case of Argentina, its Constitution, the Hazardous Waste Law (1992), and the General Environmental Law (2002) provide an exceptional framework for analysing the environmental impact of chemical activities. It is noteworthy that this legislation aligns with the directives of the European Parliament as well as with other regional legislations. Fundamentally, it is essential to raise awareness that the heads of academic units or industrial plants can be held accountable for the environmental effects caused by their activities.

Methods to prevent potentially hazardous compounds from reaching the environment will be evaluated, starting with effluent control methods with varying degrees of treatment, such as filters, decanters, catalysts, bioreactors, including incineration, neutralization, and supercritical oxidation, as discussed in the previous unit. This demonstrates that even in the best-case scenario, these processes generate waste that must be disposed of in special facilities with immobilization and control measures according to their residual hazard. Some cases reviewed in previous units are revisited to identify with the students, the chemical residues generated and to explore possibilities for remediation or disposal. In contrast, the principles of green chemistry and circular economy are presented as paradigm shifts for a more sustainable development of chemistry. Additionally, this section proposes a reflection on various research topics or activities in chemistry that students suggest, analysing them within the framework of the United Nations Sustainable Development Goals (UNSDGs).