thin layer chromatography

What is thin layer chromatography

Thin layer chromatography is a technique used to separate pigments using a thin layer of absorbent material, known as the stationary phase. After the sample has been applied to the baseline, a solvent, known as the mobile phase, moves up the material. Different pigments move up the TLC at different rates so separation is achieved.

The distance travelled by the pigment is divided by the distance travelled by the solvent to find the retention factor.

Difficulties of thin layer chromatography

Not all molecules can be seen, some are colourless. Overcome using:

• UV light

• Ninhydrin which binds to amino acids to make them visible

• Iodine gas binds to molecules

How does it work

The distance travelled by the molecules is dependent on their polarity and solubility. Exposed OH- groups of the paper form hydrogen bonds with the molecules. A highly polar solute will stick to the surface and move slowly, a non polar solute will travel quickly up the plate.