Paper Chromatography--Lab

Paper Chromatography Lab
To learn about chromatography as a chemical identification technique and to
practice skills of observation and comparison.
Use paper chromatography to identify which pen was used to write a note found at
the crime scene.
Chromatography literally means “color writing”. Chromatography is a
method for analyzing complex mixtures (such as ink) by separating them
into the chemicals from which they are made. Chromatography is used to
separate and identify all sorts of substances in police work. Drugs from
narcotics to aspirin can be identified in urine and blood samples, often
with the aid of chromatography.
Your experiment will separate inks as they move in water through paper.
The black inks will separate because each of the colored pigments that
make up the black ink have different solubility in water. They also vary
in how much they stick to the paper. The colors that move the farthest are
the most soluble in water and/or stick to the paper the least.
test pens
container of water
test paper strips (one for each pen)
chromatograph of note
1. Pour a small amount of water (about ½ - 1 inch deep) into container
2. Use one of the pens to make a dot in the middle of a test paper strip.
3. Use a pencil to label the top of the test paper strip so you will know which
pen is being tested.
4. Push a skewer through the top end of the test strip so that the strip hangs
from the skewer.
5. Repeat steps 2-4 using the remaining pens.
6. Rest the skewer across the rim of the container of water so that the bottom of
the strips just touch the water.
7. Leave test strips suspended for about 10 minutes.
 Observe how the ink bleeds and the color pigments separate as the ink
comes in contact with the water absorbed by the filter paper.
 Record your observations of the reactions and color separations
8. Compare the chromatograph for each pen with the chromatograph for the
note to determine which pen was used to write the note.
Color Pattern Observed
1. _______________|________________________________________________
2. _______________ |_______________________________________________
3. _______________|_______________________________________________
Which pen matches the chromatograph? Explain why your answer.
Pen: ____________________________________
Explanation: ______________________________________________________