Paper chromatography

Paper Chromatography

Paper chromatography is a type of partition chromatography used to separate mixtures. In this method, the stationary phase is water trapped in the fibers of paper, while the mobile phase is an organic solvent that moves over the paper via capillary action.

Types of Paper Chromatography:

Ascending Chromatography
Descending Chromatography
Radial (Circular) Chromatography

Ascending Paper Chromatography (Procedure):

In this method:

A suitable solvent mixture is placed in a chromatographic tank.
Take 20 cm of Whatman No.1 filter paper and draw a pencil line 2.5 cm from the bottom.
Apply the sample and, if needed, a known compound spot on the line.
Hang the paper vertically so the bottom edge dips 5–6 mm into the solvent.
Close the tank to create a saturated atmosphere and allow the solvent to rise.
Once the solvent front reaches about three-quarters of the paper, remove it, mark the solvent front, and let it dry.

Chromatogram:

After drying, the resulting pattern of separated spots on the paper is called a chromatogram. If the spots are colorless, detection methods such as chemical reagents or UV light may be used.

Retardation Factor (Rf):

Each compound has a specific Rf value which helps in identifying it. It is calculated using the formula:

Rf = Distance travelled by the compound ÷ Distance travelled by the solvent

Paper chromatography