Forensic Analytical Methods

Thiago R L C Paixão, Wendell K T Coltro, Maiara Oliveira Salles, Subrayal Reddy, Thiago R L C Paixão, Wendell K T Coltro, Maiara Oliveira Salles

• Éditeur: Royal Society of Chemistry
• Année: 2019
• ISBN:
  9781788018562
• Édition: 1
• Sujet: Physical Sciences
• Sous-sujet: Analytic Chemistry

Forensic analysis relates to the development of analytical methods from laboratory applications to in-field and in situ applications to resolve criminal cases. There has been a rapid expansion in the past few years in this area, which has led to an increase in the output of literature. This is the first book that brings together the understanding of the analytical techniques and how these influence the outcome of a forensic investigation.

Starting with a brief introduction of the chemical analysis for forensic application, some forensic sampling and sample preparation, the book then describes techniques used in forensic chemical sensing in order to solve crimes. The techniques describe current forensic science practices in analytical chemistry and specifically the development of portable detectors to guide the authorities in the field.

The book provides an excellent combination of current issues in forensic analytical methods for the graduates and professionals. It will cover the essential principles for students and directly relate the techniques to applications in real situations.

CHAPTER 1

Introduction to Chemical Analysis Focusing on Forensic Chemical Sensing and Detection

THIAGO R. L. C. PAIXÃO,^a† MAIARA O. SALLES^b‡ AND WENDELL K. T. COLTRO^c§

^aInstituto de Química, Universidade de São Paulo, São Paulo, Brazil 05508-900 ^bInstituto de Química, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil 21941-909 ^cInstituto de Química, Universidade Federal de Goiás, Goiânia, GO, Brazil 74690–900

^†Corresponding author. Email: [email protected] ^‡Corresponding author. Email: [email protected] ^§Corresponding author. Email: [email protected]

1.1 Introduction

Until the nineteenth century, the use of chemicals to murder someone without a trace was very common due to the absence of the analytical methods needed to test and prove the poisoning. In addition, many symptoms of chemical poisoning are very similar to those of some natural diseases. Arsenic, for example, is one of the chemicals frequently used to poison; its detection, based on chemical sensing, is one of the landmarks of Forensic Analytical Chemistry.

During a trial, a judge could consider an expert witness’s opinion of crime evidence as a fact until the court reached a verdict. In 1832, John Bodle, who was accused of murdering his grandfather by using arsenic, was put on trial in London.¹ James Marsh, a British chemist appointed as an expert witness in this trial, tried to detect arsenic in the grandfather’s stomach. Using the hydrogen sulfide test,² Marsh detected arsenic as the evidence of the crime. However, the test result degraded before it could be shown to the jury. While Bodle could not be found guilty of his grandfather’s murder, he later confessed to the crime after the jury verdict. Due to this outcome, Marsh began the research to propose a reliable test that could prove arsenic poisoning in biological tissues and could therefore be used as evidence to show a jury.

In the four years following the Bodle trial, Marsh worked hard to develop a reliable test that could be used as evidence to prove someone’s guilt in a courtroom. To achieve this goal, he set out to improve Carl Wilhelm Scheele’s test which was used to detect the existence of arsenic.³ Scheele’s method mixed arsenic powder with metallic zinc and nitric acid. This mixture was then heated, releasing the garlic aroma of arsine gas (AsH₃), which could be detected by someone. However, just like the hydrogen sulfide test used by Marsh in the Bodle case, the positive result was unreliable and could not be used in court. Hence, Marsh proposed using the ternary mixture of the Scheele’s test, reaction (1). When the arsine gas was formed, he confined the gas in a funneled tube, and heated the tube again, reaction (2). The trapped arsine gas decomposed into a gray metallic film, forming an “arsenic mirror” that could be used as evidence in the courtroom.⁴

As₂O₃ + 6 Zn + 12 H⁺ → 2 AsH₃ + 6 Zn²⁺ + 3 H₂O(1)

2 AsH₃ → 2As + 3H₂(2)

The pioneering use of the Marsh’s test as a forensic tool in a trial to prove guilt occurred in 1840 during the infamous Marie LaFarge case. In brief, the widow was accused of murdering her husband, Charles Lafarge, by adding arsenic to his food and drink. The positive test result for arsenic using Marsh’s procedure started the process which sent her to prison.⁵ The Lafarge trial was a landmark for the use of chemical sensing tests and analytical methods in murder trials, ending the impunity of poisoning cases and allowing decisions to be made in forensic cases. Hence, the development of analytical methods and the use of analytical techniques occupies an important place in modern criminal investigation, as these methods will be the tools used to detect and quantify chemicals in crime scene investigations. Currently, most analytical laboratory methods use sophisticated techniques, such as atomic absorption spectrometry (AAS)⁶ and inductively coupled plasma mass spectrometry,⁷ to detect, for example, arsenic in a biological sample. However, a new analytical method mentioned in the literature needs to be well-established or needs to meet some additional criteria before being used in court to be recognized as a Frye standard in the forensic field.

The Frye standard originates from Frye vs United States,⁸ where the systolic blood pressure deception test was used as evidence to indicate if someone was telling the truth based on a change in their blood pressure. The US made two important statements in this document:⁸

Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while the courts will go a long way in admitting experimental testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.

We think the systolic blood pressure deception test has not yet gained such standing and scientific recognition among physiological and psychological authorities as would justify the courts in admitting expert testimony deduced from the discovery, development, and experiments thus far made.

These statements show that the analytical methods or techniques need to be recognized by the scientific community before they can be used as evidence in trials. However, the real change in the criteria for the admittance of scientific analytical method evidence occurred with the Supreme Court’s 1993 decision in Daubert vs Merrell Dow.⁹ This case recognized five factors that a judge could ponder in the evaluation of an analytical method being used in a court. These factors are: “(1) whether the theory or technique can be (and has been) tested; (2) whether the theory or technique has been subjected to peer review and publication; (3) the known or...