Celestine's CSI Journal 2012: Fifth lesson: Chromatography!

For this lesson, we learnt about chromatography and its importance in forensic investigation. It is defined as "a physical separation method in which the components of a combination are separated by differences in their distribution between two phases, one of which is stationary while the other moves through it in a definite direction".

I have also learnt that there are different chromatographic processes available: gas chromatography, liquid chromatography, ion exchange chromatography, and affinity chromatography.
Ion exchange chromatography- a process that allows separation of ions and polar molecules based on their charge
Affinity chromatography- method of separating biochemical mixtures and based on a highly specific interaction such as that between antigen and antibody, enzyme and substrate.

For this lesson, we are carrying out paper chromatography with ink.

Firstly, the scenario was set:

We were given a cheque and some of the numbers at the top right corner of the cheque were forged. We were tasked to find out which digits were forged using chromatography.

We were given the cheque and a few strips of paper. Firstly, we had to draw the line which indicates the place at which we dropped our solute, using a pencil. Then, we cut out small pieces of paper with the digits individually and tried to extract the ink by using the tip of a dropper to poke the ink out of the small piece of paper in a very very tiny container containing a drop of water. Next, using the capillary tube, we obtained the ink from the container and dripped 2 drops on the starting line (pencil drawn). We then inserted the strip of paper into a boiling tube filled with approximately 2cm cube of water. The strip of paper was then left alone. We repeated the whole procedure for the rest of the digits and eventually, we found out that digits 4 and 7 were the forged ones.

This is because, based on the chromatography obtained, there different colours appeared on the chromatography, for example: the colour pink was present on the chromatographies of digits 4 and 7 but not on the rest. However, this is not the only way in which the conclusion can be made. We can also calculate the r.f values and see which chromatography(ies) has the most differing value(s). :)

Overall, i feel that chromatography can be very useful in forensic investigation because for example: similar to the scenario given, the police can find out if any legal documents are forged using the method of chromatography.

Generally, chromatography can be used to determine what is in a mixture. For example: when people go in for drug tests, their urine may be analysed using chromatography to determine if they have drugs or drug byproducts in their urine. In forensic pathology, a sample may be analysed to determine what chemicals are present in the dead body and possibly indicate if there is a poisonous substance present that may have killed them, or whether they were on drugs/ drunk when they died. Moreover, it is also possible that chromatography is used to analyse samples taken from crime scenes to find out if any unusual substances are present that might indicate where something came from or where someone may have been prior to entering the crime scene. At airports it can be used to detect minute traces of explosives!!

Thus, i felt that this whole lesson was very beneficial and it actually got me thinking about whether i was interested in the area of forensic science in the future :P hehe.

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