Chromatography - Forensic Science (full article)

Chromatography - Forensic Science 


Chromatography is an analytical process to physically separate mixtures with the purpose of identifying compounds from crime evidence during a forensic analysis.


 It is routinely used to identify and compare samples of drugs, explosives, inks and biological samples such as saliva, urine, blood and other.


To get the process started, the mixture is dissolved in a substance called the mobile phase, which carries it through a second substance which carries it through a second substance called the stationary phase.


Colour pigments from plants

Mikhail Tsvet  did so to achieve the separation of various colour pigments from plants. As a result, he named the technique “chromatography”; “chroma” from the Greek word for “colour”, combined with “graphy”, meaning writing or recording.

If a sheet of paper or cloth contacts(stationery phase) a container filled with water or alcohol in which a complex pigment is dissolved(mobile phase), capillary action will carry the mixture up the paper or cloth, but the components of the pigment will not all travel at the same rate.The largest molecules of the mixture will travel more slowly while the smallest ones race ahead, causing the stationary phase to develop discrete bands of color corresponding to each component of the mixture.


There are primarily four different types of chromatography: 

  1. Gas chromatography, 

In gas chromatography, the mixture of interest is vaporized and carried through a stationary phase (usually a metal or glass separation column) with an inert gas, usually nitrogen or helium. Larger molecules in the mixture take longer to pass through the column and reach the detector at the far end.

It's used for Toxicology, Arson Investigations, Drug Analysis.


  1.  Liquid chromatography, 

In liquid chromatography, the mixture of interest is dissolved in a liquid and passed through a solid stationary phase, which is often made of a silica material. Several varieties of liquid chromatography exist, depending on the relative polarities of the mobile and stationary phases (normal-phase versus reverse-phase) and whether the mobile phase is pressurized (high-performance).

It's used for Drug Analysis, Explosives Analysis:, Toxicology.


  1. Thin-layer chromatography, and 

In thin-layer chromatography (TLC), the stationary phase is a thin layer of solid material, usually silica-based, and the mobile phase is a liquid in which the mixture of interest is dissolved. Thin-layer chromatography comes with the advantage of photographing well, making its output easy to digitize.

Its used for Drug Identification,Trace Evidence.


  1. Ion exchange chromatography 

separates the components of a mixture based on their charge, in addition to or instead of their size. In essence, positively (cations) or negatively (anions) charged ions are separated using different stationary phases and different pH mobile phases.

A forensic scientist might use IC to analyze the residue found at the scene of an explosion.



Compiled by

Ms Naresh kuwar'


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