Practice question

Chromatographic systems are classified by the physical arrangement of stationary phase. Planar formats utilize stationary phase spread as a thin layer on a flat support, allowing capillary-driven migration. Paper chromatography employs filter paper where cellulose fibers retain bound water as stationary phase, while organic solvent moves by capillarity, exemplifying planar mode. Column systems pack stationary phase within a tube. Gas chromatography uses gaseous mobile phase. Ion exchange relies on electrostatic interaction principle, not geometry. Recognizing paper as planar clarifies its mechanism, simplicity, and use in teaching partition principles for amino acids and pigments.