BIOLOGICAL MOLECULES: Chromatography

Chromatography is done to separate a mixture into its constituents. The two key components are the stationary phase and the mobile phase.

The stationary phase is either the chromatography paper or a thin-layer chromatography (TLC) plate. The paper is made of cellulose. The TLC plate is often a sheet of plastin, coated with a thin layer of silica gel or aluminium hydroxide. In each case, it has -OH groups pointing outwards in contact with the mobile phase.

The mobile phase is the solvent for the biological molecules. At a simple level, we can use water (for polar molecules) or ethanol (for non-polar molecules). The mobile phase flows through and across the stationary phase, carrying the biological molecules with it.

Carrying out Chromatography

1) Wear eye protection

2) Draw the line in pencil and put a tiny dot to show you where to place your solution mixture - drawing in ink will confuse the experiment as the ink will also separate.

3) Spot the solution mixture onto the pencil dot several times using capillary tubing. Wait for the spot to dry before putting on the next spot - try to make these as thin as possible. When it is completely dry, lower it into the solvent. Ensure the levelof the solvent at the start is below the pencil line. 

4) Cover the beaker with a watch glass, or glass plate.

5) Let the apparatus run until the solvent has reached…