ThinLayer

Thin-layer chromatography (TLC) is an analytical technique used to separate, identify, and monitor compounds in a mixture. It relies on a thin layer of an adsorbent, typically silica gel or alumina, spread on a flat solid support such as glass, plastic, or aluminum. A small amount of sample is applied as a spot near one edge of the plate. The plate is placed in a development chamber containing a shallow layer of solvent, the mobile phase.

As the solvent moves up the plate by capillary action, mixture components partition between the mobile phase and the stationary phase. Differences in polarity, hydrogen bonding, and other interactions cause components to travel at different rates, producing distinct spots along the plate.

Visualization and measurement are common steps. After development, the plate is removed and dried. Spots may be visible under ultraviolet light if they are UV-active, or may require staining reagents. The position of spots is often described by the retention factor (Rf), defined as the distance a spot traveled divided by the distance the solvent front traveled.

Variations include normal-phase TLC, which uses a polar stationary phase and non-polar mobile phase; reversed-phase TLC, which uses a non-polar stationary phase; high-performance TLC (HPTLC) that employs finer particles and automated handling for higher resolution; and two-dimensional TLC, which develops the plate in two directions with different solvent systems.

Applications span monitoring reaction progress, assessing purity, and identifying components by comparison with standards. TLC is valued for its simplicity, speed, low cost, and small sample requirements, though it offers lower resolution and quantitative precision than high-performance liquid chromatography, requiring appropriate calibration for quantitative use.