Chemistry · General Principles Of Organic Chemistry · NEET
Paper chromatography is PARTITION chromatography, not adsorption. This is the single most tested point (asked directly in NEET 2020). In paper chromatography the chromatography paper holds water trapped in its fibres, and this trapped water is the stationary phase. Components separate by dividing (partitioning) between this stationary water and the moving solvent. It is NOT adsorption because nothing sticks onto a solid surface here.
The stationary phase stays fixed and does not move. It can be a solid (silica gel or alumina in column/TLC) or a liquid held in place (water trapped in the paper). The mobile phase moves slowly over the stationary phase and carries the components along. It can be a pure solvent, a mixture of solvents, or a gas. Separation happens because the two phases pull on each component with different strength.
Adsorption chromatography works because different compounds STICK (adsorb) onto a solid adsorbent to different degrees; column chromatography and TLC belong here and use silica gel or alumina. Partition chromatography works because components DISSOLVE and divide between two liquids to different degrees; paper chromatography belongs here (water is the stationary liquid). One-line rule: adsorption = sticking onto a solid, partition = dissolving/dividing between liquids.
Silica gel and alumina are the common adsorbents (stationary phase) in both column chromatography and TLC. They have a large surface that holds different organic compounds to different degrees. The compound that is adsorbed most strongly stays near the top of the column and moves the least; the one adsorbed weakly comes down fastest. That difference in adsorption is exactly what separates the mixture.
Column chromatography (and TLC) are ADSORPTION chromatography, because they rely on differential adsorption on a solid adsorbent (silica gel/alumina). Only paper chromatography is partition. NEET often gives four options and asks which one is partition — the answer is paper, and column/TLC/adsorption are the traps.
Paper chromatography is an example of
Try the real previous-year questions from this chapter — each with the answer and a full solution.
NCERT lists three uses: to separate a mixture into its components, to purify a compound, and to test the purity of a compound. It is described as one of the most useful modern separation and identification techniques.
The name comes from the Greek word 'chroma' meaning colour, because the method was first used to separate coloured substances found in plants.
Adsorption chromatography (which includes column chromatography and thin layer chromatography, TLC) and partition chromatography (which includes paper chromatography).
The mobile phase can be a pure solvent, a mixture of solvents, or a gas. It moves slowly over the fixed stationary phase and carries the components along at different speeds.
Column chromatography and thin layer chromatography (TLC). Both use a solid adsorbent (commonly silica gel or alumina) as the stationary phase and separate components by differential adsorption.
