To quantify the results, the distance traveled by the substance being considered is divided by the total distance traveled by the mobile phase, this ratio is called the retardation factor ( R f), or sometimes colloquially as retention factor. Chemical processes 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. Often this can be done simply by projecting ultraviolet light onto the sheet the sheets are often treated with a phosphor, and dark spots appear on the sheet where compounds absorb the light impinging on a certain area. The mobile phase may be a mixture, allowing chemists to fine-tune the bulk properties of the mobile phase.Īfter the experiment, the spots are visualized. For example, with silica gel, a very polar substance, non-polar mobile phases such as heptane are used. The mobile phase has different properties from the stationary phase. The goal of TLC is to obtain well defined, well separated spots. TLC functions on the same principle as all chromatography: a compound will have different affinities for the mobile and stationary phases, and this affects the speed at which it migrates. TLC is an analytical tool widely used because of its simplicity, relative low cost, high sensitivity, and speed of separation. It may be performed on the analytical scale as a means of monitoring the progress of a reaction, or on the preparative scale to purify small amounts of a compound. Because different analytes ascend the TLC plate at different rates, separation is achieved. After the sample has been applied on the plate, a solvent or solvent mixture (known as the mobile phase) is drawn up the plate via capillary action. This layer of adsorbent is known as the stationary phase. Thin-layer chromatography is performed on a sheet of an inert substrate such as glass, plastic, or aluminium foil, which is coated with a thin layer of adsorbent material, usually silica gel, aluminium oxide (alumina), or cellulose. Thin-layer chromatography (TLC) is a chromatography technique used to separate non-volatile mixtures. Fluorescent TLC plate under an ultraviolet (UV) light
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