What is forensic chemistry

Forensic chemistry. The art of analytics

Table of Contents

Preface

History of Forensic Chemistry

Experiment on the chemical turnaround - The Mitscherlich - sample

Toxicology - An Introduction

The analytical detection of cyanide

Dactyloscopy evidence of fingerprints

Classic chemical proof of fingerprints

Report from a famous criminal case

Other important analytical detection methods

bibliography

Preface

This specialist thesis deals with the topic of forensics, which has a great influence on forensic technology and the work of the criminal police. How can a crime be solved by chemical analysis? This question will be clarified in the course of this work, as I have tried to shed light on as many areas of chemical forensics as possible. First, the history of forensics is considered, and crimes could be solved with the help of analytics at an early stage. Then I dedicate myself to the sub-area, toxicology, which makes up a large part of chemical forensics. How toxic can substances be and what can this depend on? Another important sub-area of ​​forensic chemistry is dactyloscopy, which made today's investigation of capital crimes possible in the first place. To what extent can fingerprints be chemically detected? The knowledge gathered can now be applied to famous criminal history cases. The work ends with a presentation of further important analysis methods.

My decision to choose this topic was based on my general interest in analytics. Chemistry as a natural science has so many practical application methods that it is difficult to decide which one to use. For me, analytics is one of the most important areas of application, as it is important for both the environment and people. Forensics is only a small area that is sometimes neglected. For this reason I try to show the importance of this field of work.

Above all, I would like to thank Mr. Kluyken for his professional assistance in this work. Both with the procurement of literature and information as well as with the practical help with the experiments.

I would also like to thank Angelina Diese for the excellent preparation of the cover sheet.

The history of forensic chemistry

Explanation of terms: The term comes from lat. " Forum": Marketplace, public space (Pl. Forums). In ancient times, especially in Rome, court cases, investigations, verdicts and the resulting punishments were publicly examined in the market square. Today, forensics is understood to mean various scientific fields of work that systematically investigate, analyze and reconstruct criminal acts.[1]

Forensic science is divided into the following areas:

- Medicine with pathology
- Biology with immunology or serology
- Physics with ballistics
- Chemistry with toxicology, dactyloscopy and other analytical evidence

This work will mainly focus on chemical forensics and its analytical detection methods. In practice, several areas of science overlap. In Germany, the BKA is responsible for all forensic examinations.[2]

The beginnings of forensics:

Today's chances to solve a crime with forensic work results are very high. But in ancient times and in the Middle Ages, crimes were the order of the day and there were hardly any opportunities to find and convict the perpetrator. Even in the advanced civilization of the Egyptians, 3000 years before the birth of Christ, people knew about the effects of herbs, drugs and antidotes. Many a disagreeable person has been eliminated with poison. The most famous example of poisoning is probably Socrates, the 399 BC. Was sentenced to death for alleged blasphemy and corruption of youth. The killing agent was the hemlock, the main component of which is coniin (C8H17N), which is so toxic that even 1g is fatal for an adult. Socrates probably died of paralysis of the respiratory tract caused by coniin poisoning. In the Middle Ages, too, poisoning was popular, especially arsenic, which was soon also used in the lower social classes and was therefore also called “inheritance powder”. Sudden demise has not been directly linked to murder, as the plague, flu epidemics, and other illnesses killed many people. The first autopsy ever officially carried out took place in Bologna in 1302. Amazing for a time when Catholicism was the predominant religion in Spain, trying by all means to stop a struggle against the “divine order”. When Paracelsus systematically investigated poisons in the 16th century, harsher penalties for poisoners were also enshrined in the law. The very possession of poisonous substances was already a criminal offense and could result in many years in prisons. But there was still no way of qualitatively and systematically detecting poisons.

The "chemical turnaround":

In the 19th century, the first chemical detection methods were established, which have been favored by scientific advances. In 1814 Orfila published the first toxicological textbook, which quickly became the basis for systematic research. The Marsh test, which was developed in 1836 by the Englishman James Marsh, limits the murders caused by arsenic, since arsenic could really be detected here for the first time. In addition to arsenic, this classic detection reaction can also detect antimony and germanium. Arsenic trioxide is reduced from hydrogen to arsine. The heat of the Bunsen burner breaks this unstable compound into black, elemental arsenic and hydrogen. A typical arsenic level forms on the heated glass wall of the test tube. The hydrogen produced is traditionally detected with an oxyhydrogen sample.[3] Marsh's sample is still used in forensic medicine to this day to detect traces of arsenic in body parts. After 1836 the number of arsenic poisoning decreased. The Belgian chemist Stas managed to split off alkaloids from the body's own substances for the first time in 1850. This discovery was followed by a closer examination of the alkaloids, the majority of which are highly toxic. This characterization of the alkaloids was carried out through taste and smell tests, crystal examinations and melting point determinations. Another important detection reaction of the time of the chemical change is the Mitscherlich sample, which detects the highly toxic white phosphorus.

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[1] http://wirtschaftslexikon.gabler.de/Definition/forensik.html(28.12.2011)

[2] http://chids.online.uni-marburg.de/dachs/expvortr/649.pdf(23.12.2011)

[3] Jander-Blasius (1979): Textbook of analytical and preparative chemistry, 11th edition, p.337

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