Two fundamental principles:

Adsorption chromatography: Components adsorb onto a solid stationary phase surface (silica gel, alumina) with different strengths. More polar compounds adsorb more strongly → move slower → elute later. Used in: column chromatography, TLC.

Partition chromatography: Components distribute between two liquid phases. Stationary phase is a liquid immobilized on a solid support. Separation based on differential solubility (partition coefficient). Used in: paper chromatography (stationary = water in cellulose), GC (stationary = liquid on inert solid).

Column chromatography: Glass column packed with alumina or silica. Load sample at top → add eluent (organic solvent) → components separate as they travel down → collect fractions from bottom. Polarity order: hexane (non-polar) < CH2Cl2 < ethyl acetate < acetone < methanol < water (polar). Start with non-polar eluent → gradually increase polarity to elute strongly adsorbed compounds.

TLC: Same principle as column but faster (analytical). Spot sample at bottom of silica-coated plate → develop in solvent chamber → visualize spots. Rf = distance of spot / distance of solvent front. Rf depends on compound polarity, solvent polarity, and adsorbent activity.