Criminalistics - Methods Used in Forensic Chemistry

Criminalistics is one subdivision of forensic sciences. Forensic chemistry, one of the most important branches of criminalism defines the micro or macro-level findings of a crime, mainly by chemistry, and by laboratory analyzes and reviews based on physics, biology, geology bases. Investigates the relationship of findings to crime and makes concrete contributions to the illuminating of the crime. Criminalistics benefits from the findings of criminology. However, in terms of quality and purpose, these two branches are separated from each other.

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Forensic chemistry has developed in parallel with the developments in the science of chemistry and has been taking place within the science of chemistry since the late 19th century, but has not been effective enough until after the Second World War. After the Second World War, forensic chemistry has developed rapidly by developments in instrumental analysis techniques, leading to major developments in forensic science, making it the most important branch of science. For this reason, the date of birth of Forensic Chemistry in forensic sciences can be considered as 1950.

Forensic chemistry laboratories are the most important institutions that function in the field of forensic chemistry. Three main answers are sought by laboratory officers in these laboratories.

• What is this?
• Is there any relationship between this or others?
• Is there any object or qualification in this?

Gas Chromatography, Atomic Absorption Spectroscopy, Scanning Electron Microscopy, and other highly precise instrumental analysis techniques are the techniques used to find answer these questions.

It is very important to examine the crime in the forensic chemistry laboratory because there is a different chemical structure of every kind of physical substance found in the scene of a crime enlightenment. Blood stains, identification of the person with DNA, fingerprints, examination of whether the documents found are fake or not and larval, insect, pollen on the body and the fact that the time and place of death are determined are very important findings.

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Methods Used in Forensic Chemistry

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Fingerprint Identification

Fingerprints are an identification technique that has been used for centuries. This method is widely used in the detection of the criminal because of each person's fingerprint is different. Ninhydrin, DFO (1,8-diazafluoren-9-one), Silver Nitrate, Sudan Black, Amido Black, and Iodine are known chemicals used to identify fingerprints. Recently used technique Ninhydrin is the most commonly used chemical in determining fingerprints.

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Ninhydrin that reacts with primary and secondary amines or ammonia is when reacts with free amines, it comes in a dark blue-purple color known as Ruhemann purple. It reacts with amines on the finger, which are amino acid residues. The reason for the change of color is the schiff base that occurs at the end of the reaction. While ammonia and blue-purple color occur in primer amin, the yellow-orange colored iminium salt comes with the secondary amines.

DFO is a chemical used to take fingerprints from porous surfaces. When it reacts with the amino acids of the finger, it becomes a derivative with high fluorescence properties. At 470 nm this stimulated material emits radiation at 570 nm. This is the reason of the blue-green light resulting from fingerprint interaction.

Identification of Blood Traces

The most commonly used chemical luminol in the detection of blood traces. However, benzene reactivity, malachite reactivity, orthotolidine test, Kastle-Meyer reactivity, Van Dean reagents are also used.

The Luminol test solution is sprayed with the atomizer in the dark room on the stained garment or fabric which has been suspended or spread once. The appearance of a bright blue color indicates that it is a blood stain.

The color of the luminol is based on what we call color-based chemiluminescence when luminol is sprayed onto blood. Here, the luminol substance, if it is suspected to be blood with hydrogen peroxide, and if there are blood residues, enables the oxidation of luminol to aminophthalate by catalyzing the oxidation reaction of luminol to hydrogen peroxide in the neighboring hemoglobin Fe (II) ions. The resulting high energy amino phthalate is liberated from the excess of energy by emitting photons or light.

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Detection of The Shooter's Hand

Sometimes there are a few suspects in crimes committed using guns. In this case Hand Swabs are taken from the persons to determine who is the shooter. If the weapon is fired, the mechanism will be activated and the gunpowder will be ejected and one side will throw the spent bullet out. At this time gunpowder sticks to the hand holding gun and whether or not there is a shot can be determined by atomic absorption device.

Paint Ink Analysis

Paint is a very valid piece of evidence in the crime. As examples, if a vehicle crashes into a standing vehicle or a person, theft events, whether the documents are written by the same pen, a variety of splashing paints can be listed. Knowing the structure of the paints and ink is necessary for their analysis. The following techniques are used for paint analysis.

Thin Layer Chromatography

Because the paints are made in different formulations for different purposes, they dissolve in different solvents. The cellulosic paint is dissolved in ethyl acetate, the furnace paint is dissolved in toluene and xylene, the synthetic paint is well soluble in toluene or white spirits. Examples of paint dissolved in suitable solvent are spotted on TLC plate and separated. The paint pigments separated after drying are examined with the naked eye and under UV light.

Infrared Spectrophotometry

An analytical method that gives a characteristic spectrum for both binder and pigment of a paint. The IR spectra of the organic components of each layer of suspected and control dye flakes prepared as a very thin film are compared to each other. Infrared microscope is used in connected devices for more detailed and reliable inspection of paints.

Scanning Electron Microscopy

The inorganic components of the paints having various paints and layer structure can be identified by SEM and are very convenient for the comparison of paints. Both morphological, qualitative and quantitative analysis can be done.

Ink Analysis with TCL

The examination of the chemical composition of the writing ink on which the documents are written can confirm that known and suspicious documents are prepared by the same pen. It can even give us valuable information about the age of the writing. One of the compared doubtful inks may have been synthesized after the date the document was prepared.

TLC is a particularly suitable technique for ink comparisons. Most commercial inks, in particular ballpoint pens, are actually a mixture of several organic dyes. These dyes can be rapidly removed on the thin layer chromatographic plate. Obviously different ink colors separated into their color components can be seen on the TLC plate. Then UV light is examined at 254 nm and 366 nm. The comparison between a suspicious ink and a known ink thus reveals many properties.

Ink Analysis with UV-VIS Spectrophotometer

Aliphatic primer alcohols do not produce any absorbance in the near UV region. Methanol, ethanol and isopropanol are frequently used in the preparation of other compounds. Ethanol-soluble inks can be compared by scanning in the UV VIS region.

Comparison and Definition of Ink Paints by Capillary Electrophoresis

By means of electrophoresis, substances such as drugs, medicinal substances, explosives, inks, inorganic anions and cations can be examined in detail in perfect order. By separating the ink composition components of the inks individually by this technique, the ballpoint pen inks can be compared and each dye can be identified.

Atomic Absorption Spectroscopy

It is a method used especially in the analysis of trace metals. It deals with the total amount of metal in the sample, but the metal is not concerned with the molecular shape of the metal. For this reason, the analysis of a specific element can be done easily. This freedom overrides the separation of the analysis element from other elements. Atomic Absorption Spectroscopy is used in the laboratory for the analysis of Sb, Pb, Ba elements in hand swab samples taken from suspects with plaster bands for the purpose of detecting shot residues.

FTIR (IR Spectroscopy)

IR Spectrophotometer is used for recognition of organic and inorganic compounds. The IR region is located between the visible region and the microwave region of the electromagnetic spectrum. This region extends from about 13000 cm^-1 to about 33 cm^-1. The vast majority of applications are restricted to the area between 4000 and 667 cm ^-1, which is the base area. The wave length greater than the wavelength of the visible light forms the near IR region at 12500 to 3300 cm ^-1. The distant IR region is between 675 cm ^-1 and 250 cm ^-1. Beyond that is the microwave zone.

Gas Chromatography - Mass Spectrometer (GC-MS)

Gas chromatography is a method which is used for separating very similar mixtures and which means color separation. Extraction, crystallization and distillation methods are used as the separation method. The mass spectrometry structure can be used to identify and identify certain substances, or to illuminate the structure of new substances that are not explicitly structured. Mass spectra of each substance from gas chromatography can be taken as it can be used as a means of mass spectrometry gas chromatography where very specific qualitative and quantitative analyzes are desired.

GRIM 2 Glass Refraction Index Detection Device

The glass is the physical evidence that can provide the establishment of the suspect-victim-crime scene linkage in studies for guilty deliberation in the field of Forensic Science. It is a device through which very small glass fragments can be obtained from the scene, from the victim or from the suspect, and the refractive indices can be determined.

The refractive index is determined by placing the glass particles in a suitable liquid and observing with a microscope by changing the temperature. By precisely increasing the temperature, a temperature is reached at which the ambient temperature is the same as the refraction index of the glass particles of the refractive index of the liquid used, and at that point the image of the glass particles in the microscope disappears. Thus, the refractive index of the glass is calculated by taking advantage of the variation of the refractive index and the change of the temperature of the used liquid.

This process, which started with Bertillon's Anthropometry, has gained a different dimension today as many sciences come together. Those who work in very different branches such as medical doctors, biologists, entomologists, toxicologists, chemists, computer programmers, physicists and even meteorologists work shoulder to shoulder to crime resolution, the arrest of the criminals and release of innocence.

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References

• Instrumentation and analytical methodology in forensic science, R. E. Gaensslen, Thomas A. Kubic, Peter J. Desio, and Henry C. Lee, J. Chem. Educ., 1985
• Cody J. Mass spectrometry. In: Levine B, editor. Principles of Forensic Toxicology. AACC Press; Washington, D.C.: 2003. pp. 139–153.
• spark.parkland.edu
• Applications of SEM in Forensic Investigations
• en.wikipedia.org
• Forensic Science: An Encyclopedia of History, Methods, and Techniques