Chromatography is a method of separating out materials from a mixture.
Ink is a mixture of several dyes and therefore we can separate those
colors from one another using chromatography. When ink is exposed to
certain solvents the colors dissolve and can be separated out. When we
expose a piece of paper with ink on it to a solvent, the ink spreads
across the paper when the ink dissolves.
Some inks are water-soluble, so you can use water as the solvent. Inks
which are not water soluble are often alcohol-soluble and you can use
Isopropyl alcohol as the solvent to create your chromatograph.
Different ink pens use different types of ink and this is obvious when
you
expose the ink to a solvent. A banding pattern of the components of the
ink mixture is called a chromatograph. Follow the instructions below to
discover which pen was used to write a note.
Preparation
- Gather several black or blue pens
- Obtain a sample of the evidence (have someone use one of the pens to
write a note - your job is to figure out which pen they used)
- Cut several coffee filters into 1/2" strips
- Set up your chromatography apparatus. Place a skewer or other long
object across two supports. Place a pan underneath the skewer and fill it
about 1/2" deep with the solvent (water or alcohol).
Procedure
- Use a long 1/2" wide strip of your evidence and hang it from the
skewer so that the end just touches the solvent. Don't let the ink get
wet.
- Use each of your suspect pens to place a dark spot of ink about 1/4" -
1/2" from the end of each coffee filter strip.
- Hang these strips from the skewer so that the tips of the strips just
touch the solvent
- Allow the inks to separate for about 15 minutes
- Examine the banding patterns and determine which of your known suspect
pens is the pen used to write the note.