Chemistry · Ch 3 — Some Analytical Techniques
Thin Layer Chromatography
Thin Layer Chromatography
The TLC Plate
In Thin Layer Chromatography (TLC), a thin layer (about thick) of an adsorbent — silica gel or alumina — is spread over a glass plate, which acts as the stationary phase and is called the TLC plate or chromplate. A small spot of the mixture to be separated is applied on the chromplate roughly from one end.
Developing the Plate
The plate is then stood upright inside a closed jar containing the mobile phase, positioned so that the sample spot stays well above the level of the mobile-phase liquid. As the mobile phase rises up the plate, it carries the mixture's components along with it, each travelling a different distance depending on how strongly it is adsorbed — the more strongly adsorbed a component, the less distance it travels — and the components thereby separate.
Visualizing the Spots …
What this figure shows. A glass plate coated with a thin (about 0.2 mm) layer of adsorbent (silica gel or alumina), the chromplate, carrying a small spot of the sample mixture applied about 2 cm from its lower end; the plate is shown standing upright inside a closed jar that holds a shallow pool of mobile-phase solvent at the bottom, positioned so the sample spot itself stays above the liquid's surface, with successive stages illustrating the mobile phase rising up the plate by capillary action and carrying the mix …
What this figure shows. The same TLC chromplate after full development, now showing the sample's original single starting spot resolved into two or more separated spots lying at different heights up the plate, each spot's final position reflecting how strongly that particular component was adsorbed by the stationary phase relative to how far the mobile pha …