Quick revision of chromatography for JEE/NEET

Chromatography explained: principles, stationary & mobile phases, column vs TLC, partition and adsorption methods — concise notes for JEE/NEET & boards.

Chromatography — Principles, Types & Key Concepts

Concise, exam-ready notes on chromatography: stationary & mobile phases, column chromatography, thin-layer & paper chromatography, partition vs adsorption techniques.

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What is Chromatography?

Chromatography is a powerful physical separation technique used to separate, purify and identify components in a mixture. According to IUPAC, it involves two phases — a stationary phase and a mobile phase — with analytes partitioning between them.

Stationary & Mobile Phases — core idea

• Stationary phase: Fixed phase where components can adsorb or dissolve. Comes as packed columns (column chromatography), thin layers on plates (TLC), or paper pores (paper chromatography).
• Mobile phase: Fluid that moves through or over the stationary phase — can be a liquid or a gas. Movement of components depends on their affinity to each phase.

Column Chromatography vs Thin-Layer Chromatography (TLC)

Column chromatography: Stationary phase is packed into a column; the mobile phase flows through under gravity or pressure. Great for preparative separation and purification.

Thin-Layer Chromatography (TLC): Stationary phase is a thin film (silica or alumina) coated on glass or plastic; the mobile phase rises by capillary action. TLC is fast, analytical and useful for monitoring reactions.

Partition Chromatography (Paper Chromatography)

Partition chromatography uses a thin film of liquid stationary phase adsorbed on an inert support; the mobile phase is usually a liquid or gas. Paper chromatography is a classical example: liquid retained in paper pores acts as the stationary phase while another liquid moves through, separating solutes by partitioning and adsorption.

Adsorption Chromatography

In adsorption chromatography the stationary phase is a finely divided solid (e.g., silica gel, alumina) and the mobile phase is typically liquid. Separation occurs because different components adsorb to the solid surface to different extents — stronger adsorption → slower movement.

Key Mechanism — Equilibrium Between Phases

All chromatographic separations are driven by an equilibrium: analyte molecules constantly distribute between the mobile and stationary phases. Components that interact strongly with the stationary phase spend more time bound and therefore move slower; components with weaker interaction move faster with the mobile phase.

Practical Tips & Exam Points

• Remember: Rf value in TLC = distance travelled by solute / distance travelled by solvent front — used for qualitative identification.
• Column chromatography is ideal for preparative separations; TLC is ideal for quick checks and analytical purposes.
• Partition vs adsorption: partition involves distribution between two liquids (one immobilized), adsorption involves surface binding to a solid.
• Polarity matters: polar solutes prefer polar stationary phases (e.g., silica) and move slower in non-polar mobile phases.

Summary — What to Remember

1. Chromatography = separation technique using stationary + mobile phases.
2. Stationary phase forms: packed columns, thin layers, or paper pores.
3. TLC uses capillary action; column chromatography uses mobile phase flow through a packed column.
4. Partition chromatography = liquid film on inert support (paper chromatography example).
5. Adsorption chromatography = separation by selective adsorption on a solid surface.
6. Stronger interaction with stationary phase → slower migration in the mobile phase.

Related resources: Physical Chemistry notes • Practice Tests

Conclusion: Chromatography is a versatile technique — understand stationary/mobile phases and how molecules partition to master problems in JEE/NEET and board exams.

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