Paper Chromatography Overview

Overview

This lecture explains paper chromatography, including its procedure, theory (mobile and stationary phases), and how to calculate Rf values.

Chromatography is an analytical technique used to separate substances in a mixture for identification.
Paper chromatography specifically separates different dyes in an ink sample.

Draw a pencil baseline near the bottom of filter paper.
Place a spot of the ink sample onto the baseline.
Add a shallow layer of solvent (e.g., water or ethanol) to a beaker.
Place the paper in the beaker, ensuring the baseline is above the solvent.
Optionally, cover the beaker to prevent solvent evaporation.
Allow the solvent to travel up the paper, carrying the different dyes.
Dyes that are more soluble move faster and farther; less soluble dyes lag behind.
Insoluble chemicals will stay at the baseline.
Remove the paper before the solvent reaches the top and let it dry, forming a chromatogram.

The mobile phase is the solvent (liquid or gas) that moves the molecules.
The stationary phase is the filter paper (solid) that the molecules temporarily bind to.
Chemicals continuously switch between the mobile and stationary phases during the process.
Movement rate depends on how soluble a substance is in the solvent and its attraction to the paper.

Rf value = (distance travelled by substance) ÷ (distance travelled by solvent).
Example: If dye moves 6 cm and solvent moves 10 cm, Rf = 6/10 = 0.6.
Rf values are used for substance identification by comparing to values in databooks.
Rf values vary depending on the solvent and type of paper used.

Chromatogram — The pattern of spots formed after chromatography, showing separated substances.
Mobile phase — The liquid or gas (solvent) that moves molecules in chromatography.
Stationary phase — The solid (paper) that molecules temporarily bind to in chromatography.
Rf value — A ratio showing how far a substance travels compared to the solvent.