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Sometimes, more than one substance is dissolved in a solution.
Chromatography is a technique that is used to separate different dissolved substances from one another.
It can be used to separate the multiple different dyes in a drop of ink - look how many are in just one single drop of ink below!
Chromatography can be used by scientists to analyse samples of water in order to find out how much of certain chemicals are in the water.
DNA fingerprinting, which was invented by Professor Sir Alex Jeffreys in 1984 at the University of Leicester, is based on chromatography and is used to identify criminals by their DNA samples. Samples of blood or skin can also be compared by the police using chromatography.
Method
The sample liquids to be tested are dropped onto special paper. The bottom of the paper is dipped in a suitable solvent (this can be water or another liquid). The different-sized particles that make up the samples travel through the paper at different speeds, so they separate at different distances.
The picture below shows the chromatography results for four different inks. Its called a chromatogram. The colours they separated into can be seen by looking at the coloured dots that appear directly above the names of the different inks.
So you can see that the brown ink is actually made up of three colours - blue, yellow and red!
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