States of Matter and Mixtures: Chromatography

Chromatography is a physical method used to separate mixtures into their individual components. These mixtures are often complex, and their individual components could be hard to identify without such a method.
The central principle behind chromatography is that different chemicals will move at different rates when transported by a liquid. This liquid is often called the “mobile phase”, and the stationary substance (like paper) that this liquid moves through is often called the “stationary phase”.
In paper chromatography, the sample is applied to a point near one end of the paper, known as the baseline. The paper is then dipped into a solvent, making sure that the initial spot where the sample was placed doesn’t touch the solvent.
As the solvent rises up the paper (by capillary action) it carries along with it the components of the sample.
Different components will travel at different rates, thus they get separated on paper. The different rates of movement occur because the components have different solubilities in the solvent and different affinities for the paper.
The end result of chromatography is a chromatogram, which is a visual display of the composition of the mixture.
After carrying out paper chromatography, a component can be identified by calculating its Rf value. To calculate the Rf value, divide the distance travelled by the component by the distance travelled by the solvent. Each substance has a characteristic Rf value in a given solvent.
Chromatography can be used in many contexts: to identify the components of inks, dyes and plant pigments; to test for certain substances in blood or urine; to purify and identify compounds obtained from natural sources like plant extracts.
Remember, like all laboratory methods, chromatography must be used with care. Proper laboratory practises and safety precautions must always be observed.