Chromotagraphy

Separation of Inks

Inks are a mixture of dyes in a solvent, normally water. They can be separated to see which dyes have been used to make a given coloured ink using simple paper chromatography.

Equipment:

1. Inks for testing - water-based
2. Chromatography paper
3. Water
4. Ruler
5. Pencil
6. Dropper pipette or narrow glass rob
7. Beaker or container for water
8. Clamp stand with clamp or bulldog clips

Method:

1. Draw a line across the width of the chromatography paper about 4 to 5 cm from the bottom.
2. Using the pipette or the glass rob, place a small drop of ink on the pencil line. Allow it to dry then add drops to build up a concentrated spot of the ink. Do not add too much at once or the results will be too spread out and hard to find the Rf values.
3. If using more than one ink per paper keep each spot on the pencil line and separated by at least 3 cm.
4. Add a shallow layer of water to the container.
5. Suspend the chromatography paper into the water ensuring the water line is at least 1 cm below the pencil line or the bottom of the largest spot of ink.
6. Leave undisturbed until the water has moved up the paper to within a few cm of the top of the paper.
7. ÷Carefully remove the paper and draw a line to make the point the water has reached near the top of the paper - use a pencil NOT a pen.
8. Allow it to dry for a few hours.
9. Measure the distance from the original pencil line to each of
10. The water-mark at the top of the paper (distance moved by the solvent).
11. The top of each of the separate dyes for each ink used. (distance moved by the dyes)
12. Calculate the Rf values for each dye.

RF = distance moved by the dye ÷ distance moved by the water (solvent).

Setup:

Rf Values