Thin layer chromatography
spotted plate
in tank with
mobile phase
mobile phase
creeping up
fully developed
In thin layer chromatography the stationary phase is a layer of silica on an aluminium backing plate.
The diagram shows a thin layer plate where a mixture has been applied at the left side and a pure substance at the right.
The diagram shows a thin layer plate where a mixture has been applied at the left side and a pure substance at the right.
The separation is accomplished by passing a mobile phase (solvent) over the stationary phase.
In thin layer chromatography, the plate is immersed in a vessel containing the solvent to a depth no higher than the level at which the plate was spotted.
As the solvent moves through the spot and up the plate, the mixture is separated because some components move farther than others.
The fact that the pure substance moves to the same amount as one component of the mixture indicates that this pure substance may be one of the components present in the mixture.
As the solvent moves through the spot and up the plate, the mixture is separated because some components move farther than others.
The fact that the pure substance moves to the same amount as one component of the mixture indicates that this pure substance may be one of the components present in the mixture.
The plate is removed from the chromatography tank when the solvent front is close to, but not at the top of the plate.
The stationary phase "retards" some substances to a greater extent than others. The extent to which substances move on the thin layer plate in a particular mobile phase is a characteristic of the substance is known as the Rf (retardation factor).
The Rf for each spot can be calculated as shown below.
The position of spotting is shown by the line just up from the bottom of the plate.
Rf values are between 0 and 1.
| Rf = | distance the spot travels from position of spotting |
| distance the solvent front travels from position of spotting |