Forensic scientists can learn who’s been involved with a crime by matching suspects’ DNA, fingerprints, hair, or clothing fibers to those found at the crime scene. Another way to make a connection is to look closely at the ink used to write a note at the scene, and compare it to the ink used by suspects at their homes and jobs.
In this activity, kids will learn that the color they see is actually made up of a combination of colors. Chromatography is used in forensic science to separate and analyze the pigments — in this case, in ink.
1. Gather three different pens with black ink from around the house.
2. Cut three strips of chromatography paper in half. Make a large dot about ½-inch from the bottom of a strip of chromatography paper, cut in half. Repeat so you have three strips, each with a dot from a different pen. Have someone write a short note on a piece of the chromatography paper using one of the pens, without letting you know which pen they used.
3. Use the binder clip to attach the top of the paper strips with the dots to the splint. Place the splint across the top of the beaker so the paper hangs
down inside.
4. Dilute the isopropyl alcohol and carefully pour just enough into the beaker to touch the bottom of the paper, but not the dot.
5. The alcohol will creep up the paper. When it reaches the top of the paper, remove from the beaker and let dry.
6. Do the same procedure with the note. Once it’s dry, compare it to the dot samples to try to determine which pen was used to write the note, by comparing the Rf value of chromatography spreads.
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