Chemistry in Forensic Science
Essentially, forensic chemistry is the application of chemistry in criminal justice, i.e. when proving crimes in courts of law. Historically, forensic chemistry has been used in analysing and identifying poisons (by methods developed by scientists) that had been used when committing murder. The Marsh test was the first test developed for the analysis of the poison Arsenic. It was named after the British scientist who created it, James Marsh. Everything from chromatography to the invention of the spectroscope (which aided in identifying chemicals as evidence) demonstrated their usefulness in the field of forensic chemistry. Moreover, Alan Walsh invented the first atomic absorption spectrometer for the detection of poisons like arsenic and cadmium (Kanojia, 2021).
Although historically forensic chemistry has been used primarily for homicides, today it is also applicable in cases of sexual assaults, suicides, pesticides and others. Zooming into cases relating to homicides or sexual assault, forensic science makes use of chemistry in 3 predominant ways: through the analysis of blood, through DNA forensics and through the analysis of firearms. Depending on the case, these methods can either be used in conjunction or independently.
The first application, blood analysis, is generally used to identify the presence of chemical substances in the blood of the victim. This is carried out by the use of a chromatography test. Chromatography is the separation of a mixture into its components. It is commonly used in laboratories to reveal unknown elements of mixtures (Santa Monica College, 2020). In forensic science, scientists use intense heat to separate blood into its components in order to determine levels of alcohol or medications consumed by the victim.
The second application, DNA forensics, is used to compare the DNA of possible suspects to that of skin, hair or blood cells left at the crime scene. This identification is carried out by an STR analysis. STR or Short Tandem Repeat analysis analyses regions of DNA that do not code for proteins. These regions are called “variable number short tandem repeats” as they greatly vary from person to person. Since almost 99.9% of our DNA is the same as everyone else, an STR analysis is especially useful when distinguishing two individuals (“What is STR analysis?,” 2011). Results are then compared to DNA profiles of individuals in a database called CODIS or Combined DNA Index System. This can also aid in the identification of suspects.
The third and final general application is firearms analysis. Crimes involving the use of firearms will almost always require chemistry to reveal information about the residue left behind by bullets or other weaponry. These are analysed by techniques like Scanning Electron Microscopy (SEM), Neutron Activation Analysis (NAA) and others. In SEM, a scanning electron microscope is used to focus a beam of electrons and produce images of a sample. The beam of electrons also interacts with the atoms of the sample which results in the formation of a variety of signals, providing scientists with valuable information regarding the composition of the sample (which could be gunshot residue or post-explosion residue) (“Scanning electron microscopy,” 2020).
A forensic chemist is one who works primarily in laboratories, repeatedly performing experiments to prove the evidence found in the court of law. Forensic chemists are able to do this by making a detailed, scientific report called expert testimony. Great measures are undertaken to avoid the contamination of evidence (which includes poisons, alcohol sample, fluids like urine and blood and even tissue samples). Precautions include wearing special protective clothing, use of sterile glassware, etc. The ‘expert testimony’ written by the forensic chemist should be such that it is easily understood by a layman, especially since the jury (in the US) consists of common people (Kanojia, 2021).
Besides criminal justice, forensics is also helpful in research carried out in hospitals, in food industries and in general chemical industries.
Kanojia, S. (2021, April 16). Forensic chemistry | Applications of forensic chemistry | ScienceMonk. Everything In Science- Physics, Chemistry, Biology and Space. https://sciencemonk.com/forensic-chemistry-applications-of-forensic chemistry/#Collection_And_Preservation_Of_The_Chemical_Evidences-Forensic_Chemistry
Santa Monica College. (2020, July 14). 2: Paper chromatography of gel ink pens (Experiment). Chemistry LibreTexts. https://chem.libretexts.org/Ancillary_Materials/Laboratory_Experiments/Wet_Lab_Experiments/General_Chemistry_Labs/Online_Chemistry_Lab_Manual/Chem_9_Experiments/02%3A_Paper_Chromatography_of_Gel_Ink_Pens_(Experiment)#:~:text=Chromatography%20is%20a%20method%20of,identify%20unknown%20components%20in%20mixtures.&text=Chromatography%20can%20be%20used%20to,chemical%20composition%20of%20many%20substances
Scanning electron microscopy. (2020, August 19). Nanoscience Instruments. https://www.nanoscience.com/techniques/scanning-electron-microscopy/
What is STR analysis? (2011, March 2). National Institute of Justice. https://nij.ojp.gov/topics/articles/what-str-analysis