Sophie Duncan looks at colourful ways to investigate chromatography

30th May 2003 at 01:00
Sophie Duncan looks at colourful ways to investigate chromatography

One hundred years ago, a Russian scientist developed a process called chromatography - writing with colours. Mikhail Tswett used this process to separate plant pigment. Since then, it has become an important analytical technique, used to separate many different types of material.

Chromatography need not be complicated. Here's an easy experiment to carry out in the classroom.

Cut some blotting paper into strips, 2cm across and 10cm long. Draw a thick line on each strip with differently coloured soluble felt-tip pens. (The markers used for OHTs work well, and dark colours tend to yield more interesting results.) Put a small amount of water into the bottom of a beaker. Place a pencil over the top and secure one of the strips to the pencil with sticky tape, making sure that the end of the paper is in the water but the line of the felt-tip is above the water surface. Wait.

The water will be drawn up the blotting paper, and different coloured lines appear. The various molecules in the ink behave in different ways when the water reaches them, and some types travel further than others.

This means the ink is split into its constituent parts. Remove the paper before the water reaches the top and leave it to dry.

You can use this technique to work out which pen wrote the note in a crime scene, to determine the colours of pigment in an autumn leaf, or to find out the colours added to sweets.

You can also use different techniques to create beautiful chromatography art.

Take circles of blotting paper and draw a number of concentric circles with pens of different colours, leaving lots of space between them. Use a pipette to put several drops of water in the centre and wait. The colours should spread and merge, creating lovely pieces every time.

Sophie Duncan is project manager for science at the BBC www.bbc.co.ukscience

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