Identification of Leaf Pigments by Paper Chromatography

Chlorophylls are the pigments that lend leaves their dark green color.

Chromatography offers chemists a powerful way to separate compounds in a complex mixture. While some chromatographic techniques such as HPLC or GC-MS require advanced equipment, paper chromatography is not only useful but simple and easy to perform.

History

In the early 20th century, Russian biologist M.S. Tsvet wanted to find a way to separate pigments in leaves. Dubbed "color writing" or chromatography, the technique he invented is the ancestor of all chromatography methods in use today.

Features

In paper chromatography, a drop of the leaf pigments is added to the bottom of a sheet of paper. Next, the tip of the paper is suspended in a shallow layer of solvent in the bottom of a beaker or other container. The container is typically kept covered to keep the solvent from evaporating.

Function

Over the ensuing minutes and hours, the pigments will gradually climb the sheet through capillary action. Depending on the structure of each molecule and the way it interacts with molecules in the paper, different pigments will ascend at different rates and become separated into distinct bands.

References

• "Chemical Principles, the Quest for Insight, 4th Edition"; Peter Atkins and Loretta Jones; 2008
• ChemGuide UK: Paper Chromatography