forensic dna analysis

Forensic chemistry

Forensic chemistry is a division of forensic science in which physical or chemical evidence is examined and tested, forensic chemistry draws general chemistry principles and ideas.

Investigating the physical and chemical properties of a substance is a major objective of analytical chemistry and forensic chemistry.

The functioning of forensic chemistry would not possible without recognition for these properties and therefore the methodology of general chemistry.

Physical and chemical properties recall that physical properties are properties of a substance that will be described or displayed without requiring an action.

For example, as we know sulfur is yellow in colour, Iron is malleable (that is it can be converted into sheets by some external forces), cocaine is white colour solid crystals, and therefore the density of a glass fragment broken from a glass window at a place where crime occurs (scene of the crime) is approximately 2.5g/ml.

Consequently, the identification of an uncommon drug will be challenging.

Two types of analysis are used in forensic chemistry for identifying the unknown substance:

Presumptive and Confirmatory Analysis:

Presumptive analyses observe chemical and physical properties that are confirmatory. Presumptive analyses examine the chemical and physical properties which are not unique enough for the examiner for identification but those analyses provide enough information to precise the search in the investigation.

Presumption analyses are usually fast and cheap to perform.

When the presumptive analyses are tested negative then they exclude potential drug candidates, once they are tested positive, after that they are forwarded to the forensic expert for their further applicable confirmatory analyses.

It should be noted that presumptive analyses only shorten a substance's possible identities, but the confirmatory analyses identify a questioned sample completely.

The court required these analysis reports and they must be performed to convict someone for custody of the illegal substance.

These analyses use the unique chemical or physical properties of a substance for the aim of identification.

Basically, confirmatory analyses are long or time-consuming and are more expensive than presumptive analyses

An advanced instrument that is used by the forensic chemist these days is the Fourier Transform Infrared Spectrophotometer (FTIR) with the help of this instrument, the forensic scientist can begin to easily find in the questioned sample by measuring its unique interaction with the infrared radiation that is emitted by the instrument.

This pattern of interaction, which could be a function of wavelength and radiations, is commonly called a chemical fingerprint. It is very unique for a pure substance and allows the substance for its identification.

After advancement in science, we have an instrument that is used when we have a compound that may be a mixture, that will be separated and by this, every compound can subsequently be identified by an instrument called a gas chromatograph-mass spectrometer (GC-MS).

The anthropometry identification system was replaced by fingerprinting after 20 years, a more accurate identification system.

Comparative analyses: 

Classification and Individualization.

The purpose of a comparative analysis is to link a questioned sample and a known sample for a common origin.

The origin may also broad which leads to classification or the exclusive that leads to individualization. for example, within the case of a hair sample analysis, its identification is commonly obvious or even easily established within the laboratory.

In fact, the value of the hair sample in forensic evidence is not found in its identification in peace of hair. The more important is, to investigate the source or origin of the sample during a particular species or individual.

This could also be determined through comparative analysis with different samples of a known origin.

The class characteristics are properties of a substance that are divided by a bunch of drugs but they don't look to be unique to any other substances of one origin.

A class characteristic that varies within a substance is named natural variation.