TLC is an inexpensive chromatography technique used to separate non-volatile mixtures. Samples are applied to a plate (normally glass or plastic) that has been coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide, or cellulose.
After the sample has been applied on the plate, a solvent or solvent mixture is drawn up the plate via capillary action. Because different analytes ascend the TLC plate at different rates, separation is achieved.
After the experiment, the spots are visualized. Often this can be done simply by projecting ultraviolet light onto the sheet; the sheets are treated with a phosphor, and dark spots appear on the sheet where compounds absorb the light impinging on a certain area. Chemical derivitizaton can also be used to visualize spots; anisaldehyde, for example, forms colored adducts with many compounds, and sulfuric acid will char most organic compounds, leaving a dark spot on the sheet.