Required Practical: Chromatography

You can carry out chromatography to separate and identify different components in a mixture such as INK or FOOD COLOURING.

Method

• Draw a PENCIL LINE near the bottom of the chromatography paper.
• Place dots of KNOWN DYE COLOURS and a dot of the INK being investigated.
• Place the bottom of the paper IN THE SOLVENT, making sure the pencil line is ABOVE the solvent.
• The solvent will move up the paper, taking the substances with it.
• Before the solvent reaches the top, remove the paper and let it dry to see the CHROMATOGRAM.
• Compare the positions of the dots on the KNOWN DYES to those of the INK.

Chromatogram Analysis

Let's look at a chromatogram on an ink and 3 different dyes:

You can see that the ink has 3 DYES, two of which are known and one that is unknown.

You can tell by matching the heights of the components and assuming the ones at the SAME HEIGHTS have the same Rf values, so are the SAME SUBSTANCES.

Therefore the ink contains DYE 1 and DYE 2 but does NOT contain DYE 3, as it is at a completely different height to the others.