Chemistry - Paper and thin-layer chromatography
Paper and thin-layer chromatography
In paper chromatography, the stationary phase is a piece of high-quality
absorbent paper, similar to filter paper.
In thin-layer chromatography, the stationary phase is a thin layer of a
fine powder, such as alumina, spread on a glass or plastic plate.
A small spot of the substance being analysed is placed on the paper or
thin layer. The paper or material supporting the thin layer is then placed
in a shallow dish of solvent. The solvent moves up the paper or thin layer.
The different components of a mixture will move up the paper or thin layer
at different rates - depending on the relative strength of their attraction
to the stationary and mobile phases - and produce a chromatogram. In the
chromatogram shown here, component A was more strongly attracted to the
mobile phase than was component B. Component B was more strongly attracted
to the stationary phase than was component A.
Rf values are determined according to
The main application of paper and thin-layer chromatography is in
qualitative analysis, i.e. to check the presence of a particular compound
in a mixture
However, an_ R_f value alone cannot tell us anything.
Reference to a file of _ R_f values obtained under the same experimental
conditions is an effective way of identifying a particular compound.
Alternatively, if the identity of the compound is suspected, a chromatogram
of the pure compound under the same experimental conditions should give the
same _ R_f value.
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