Experiment 16: Chromatography

Date

2 April 2007 by Hunters. Links in with Chapter 16 of our book.

Safety

Methylated spirits is flammable.

Aim

To use paper chromatography to separate inks into their base colours (component dyes).

Method

Cut filter paper into strips about 12mm wide.

Choose a pen and draw a dot 1cm from one end of the strip. Write the name or description of the pen on the other end of the paper strip to identify the strip.

Place half a centimetre depth of methylated spirits in a beaker.

Place the strips vertically in a beaker with the dot at the bottom end.

Use a blank strip (no ink dot) as a control strip to see what a strip with just methylated spirits looks like.

Equipment

Selection of ballpoint pens of various colours.
Methylated spirits.
Filter paper, scissors.
Glass beakers.

Results/Observations

Some inks took a while to start separating while others started separating straight away. Some inks separated into four or five colours while others did not separate or separated into only two colours. All the samples had a thin horizontal purple line on them.

Inca mask pen separated into cyan, black, yellow and pink. Widely regarded as the prettiest separation.

Red pen separated into orange, yellow and pink.

Control strip produced a single purple line across it.

Green gel pen did not separate into different colours and only a small amount of ink was carried up the filter paper.

Conclusion

Most common inks are made from more than one colour of dye. Different inks that look similar can separate into different numbers of colours.

The purple dye common in methylated spirits is also carried up the filter paper and this caused a purple line on all our specimens. Ideally colourless methylated spirits would be used.

Methylated spirits appears to not be a good solvent for a green gel pen.

Chromatography is a good way to separate (or filter) small particles like dye particles, and can thus be used to identify substances from their constituents.

Discussion

Capillary action is what causes the methylated spirits to rise up the filter paper.