Science | Science Experiment of the Week 8 | 284 - Chromatography

Forensics, Crime Detection, Poisons, Chemical Evidence - Chromatography is the science of separating chemicals as they are carried along by a liquid. In the world of forensics, chromatography is used to separate chemicals to look for and identify possible poisons and other chemical evidence.

This Week's Experiment - #284 Chromatography

These experiments are from Robert Krampf - The Happy Scientist

This week's experiment started with a request that I got from a homeschooling family in Australia. Louise wrote asking for experiments dealing with forensics. What are forensics? It is the science of crime detection. I sent her past experiments on fingerprints and footprints. I was writing instructions for chromatography when I realized that it would make a good experiment for this week. To learn about chromatography, you will need:

coffee filters
several kinds of black ink pens (not indelible ink)
a small drinking glass
water
scissors

Carefully use the scissors to cut the coffee filter into strips about an inch wide. Pick one of the strips and make a fold about 1/2 inch from one end, so that the strip will hang over the side of the glass. About an inch from the other end, use one of the black ink pens to make a round dot about the size of this "0".

Hang the strip inside the glass and carefully add water until the bottom 1/2 inch of the strip is in the water. This should put the dot about 1/2 inch above the water. Quickly the water will begin to soak into the strip, and you can see the moisture climbing. As it passes the dot, you should start to see the ink dissolving and running.

Over the next few minutes, something very interesting should happen. As the ink dissolves in the rising water, it should separate into bands of different colors.

What you are seeing is the science of chromatography at work. Chromatography is the science of separating chemicals as they are carried along by a liquid. The idea is that the black ink is made by mixing several different colors. Some of the inks stick to the paper more than others. The less they stick to the paper; the faster the ink travels with the water, so the band of color that is farthest from the original dot is the ink that is least attracted to the paper. Density also plays a part, with denser inks traveling slower.

If you try black ink from different brands of pen, you will find that they use different recipes. A common activity when museums teach a forensics class for students is to have students use chromatography to find out which suspect's pen was used to write a mysterious note.

You can try other colors of ink, and you can even write on the same dot with several colors of pen. This can lead to some very artistic patterns. In a past experiment we did a similar demonstration with brown M&M candy, which is a good excuse to get some and eat all the other colors. In the world of forensics, chromatography is used to separate chemicals to look for and identify possible poisons and other chemical evidence. Not as much fun as the M&M's, but still pretty cool stuff.

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