National Chemistry Week - Experiments - Radial Paper Chromatography

Materials:

• two pieces of filter paper (11 centimeters diameter or large works best)
• a plastic cup
• several different felt pens (black felt pens generally give the best results)

Procedure: First piece of filter paper

1. This paper will be your chromatogram (the paper used to separate the ink dyes).
2. Poke a small hole in the center of the filter paper.
3. With one pen, equally space 6 small dots around the circumference of a small circle about 7 mm from the centre hole.

1. From the second piece of filter paper, cut out a small piece in the shape of a triangle that is 4 cm tall and 2 cm at its base.
2. Fold or roll this triangle into a cone.
3. Place the pointed end of the cone into the hole of the dotted piece of filter paper prepared above. The cone will serve as a water wick.
4. Fill the plastic cup with water to within 1 cm of the top. It is very important to dry the rim of the cup with a paper towel before proceeding any further.
5. Place the spotted piece of filter paper over the cup so that it rests on the rim with the wick extending down into the water.
6. The water will travel up the cone to the filter paper, wetting the filter paper in a circular pattern. When the water reaches the ink spots, the radial chromatography pattern begins to develop.
7. Allow your chromatogram to develop until the water has spread to about 1 cm from the outer edge of the filter paper. This takes about 5 to 10 minutes depending on the size of the filter paper.
8. Remove the filter paper and allow it to dry.
9. Repeat the experiment with a different pen.

Note: The filter paper can be replace by a coffee filter that is cut into the shape of a circle. This experiment has been adapted from the article by Robert Becker, John Ihde, Kersti Cox and Jerry Sarquis, Journal of Chemical Education, Vol. 69, No. 12, pp 979-980.