Chromatography is a technique used to separate and identify different components in a mixture. It works by making the different substances move at different speeds through a stationary phase while being carried by a mobile phase.

• Stationary Phase: The fixed material that the mixture moves through (e.g., paper, silica gel).

• Mobile Phase: The solvent that carries the mixture through the stationary phase (e.g., water, ethanol).

• Separation Principle: Different components move at different speeds based on their size, solubility, or affinity to the phases.

Types:

• Paper Chromatography:

  • Used for separating pigments, inks, or food dyes.

  • A drop of the mixture is placed on filter paper, and the solvent carries the components upward.

  • Different substances travel different distances.

• Thin Layer Chromatography (TLC):

  • Similar to paper chromatography but uses a glass plate coated with a thin layer of silica or alumina.

  • Provides faster and better separation.

• Gas Chromatography (GC):

  • Used for volatile substances.

  • A gas acts as the mobile phase, carrying the sample through a tube coated with the stationary phase.

• Liquid Chromatography (LC):

  • Used for non-volatile substances.

  • Often used in medical and drug testing.

Rf Value:

The Rf value helps identify the separated substances:

Rf = Distance moved by the solvent/Distance moved by the substance​

• Rf values are always less than 1.

• Each substance has a unique Rf value in a given solvent.