Most products we obtain from nature are mixtures containing a multitude of different substances. Usually we use only one or few of these substances due to their special effects. So the first step for gaining natural products is often a purification. E.g. if a medicament is required from herbs first you have an extraction process followed by a purification; after that it might be used.
The most important method to separate and identify substances is called chromatography. There are various types of chromatography all based on the same principle: A mixture is transported by a mobile phase (liquid or gas) along a so-called stationary phase which is a solid usually made of silica or cellulose.
Depending on the solubility (if a carrier liquid is used) and adhesion forces with the solid the more or less of a substance is transported along the stationary phase
(depending on size or charge of the substance) and hence a mixture separated.


Thin layer chromatography of paprika powder

By using the so-called thin layer-chromatography the stationary phase is a plastic foil with a surface of silica or cellulose.
An extract of paprika powder shall be separated in our example.

Let the teacher demonstrate the following description!

A thin layer-sheet is prepared by careful drawing - with a ruler and a pencil - a line
ca. 1[cm] from the bottom.
The extract is obtained by giving 1-2 spatula of paprika powder into a test-tube and adding a few [ml] of acetone. Shake well and allow to settle; the liquid should be
reddish. With special capillary glass-rods the extract is repeatedly given on the start line of the chromatography-sheet.
A development-chamber is prepared by giving a mixture of naphta (b.p. range 100 - 150 [°C] ) and propanol-2 with a ratio 10 : 1 into a glass-cylinder. The cylinder should be covered so that the solvents remain in the chamber.
Now the prepared chromatography sheet can be given into the development chamber. Development can be interrupted if the liquid is around 4/5 to the top of the sheet.

How many different components can you identify?

Repeat the experiment but use as mobile phase in the chamber

I pure naphta     II pure propanol-2     III pure acetone

Read on the topic! - What other types of chromatography exist? -
What is a R_F-value?