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.
- Inks for testing - water-based
- Chromatography paper
- Dropper pipette or narrow glass rob
- Beaker or container for water
- Clamp stand with clamp or bulldog clips
- Draw a line across the width of the chromatography paper about 4 to 5 cm from the bottom.
- 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.
- If using more than one ink per paper keep each spot on the pencil line and separated by at least 3 cm.
- Add a shallow layer of water to the container.
- 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.
- Leave undisturbed until the water has moved up the paper to within a few cm of the top of the paper.
- ÷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.
- Allow it to dry for a few hours.
- Measure the distance from the original pencil line to each of
- The water-mark at the top of the paper (distance moved by the solvent).
- The top of each of the separate dyes for each ink used. (distance moved by the dyes)
- Calculate the Rf values for each dye.
RF = distance moved by the dye ÷ distance moved by the water (solvent).