The Chromatography Detectives

Experiment Design by Jan Rossi,  Webpage and Screenplay by Tony Alfrey - Lucille M. Nixon Elementary School Parents.



Some evildoer (is that really a word?) at Nixon Elementary has been disguising himself/herself as our school principal and has been secretly buying marshmallows for the whole school.  Who could it be?  The detectives found a handwriting sample at the local supermarket where the marshmallow suspect used a black marker to write on a credit card slip.  Then, four suspects were found at the market in the marshmallow section.  Each suspect was carrying a black marker.  Which of these four suspects could be guilty?  Is this a task for the National Security Administration?  No, this is a job for the Nixon Noon Scientists!

© Jay Ward Productions.

Solving the Crime: The Kids Get To Work!


1. The Evidence

The markers were labeled "1" to "4" (corresponding to the four suspects, of course).  For your test of this experiment, select four different small-tip, black felt markers that you might find at an office supply store.


2. Preparing The Test

Cut out five strips of filter paper (coffee filter paper works well) about 1" wide and 4-5" long.


3. Keep Going

Ink from the credit card slip was removed using Special Equipment (conveniently loaned by the NSA), and some of this ink was used to draw a line about 1" from the end of one strip of filter paper.  For your experiment, have a friend or teacher secretly draw a line on a piece of the filter paper using one of the four markers. Of course, your friend should not tell you which marker they used, because you're going to figure this out, right?  Make sure you put two ?? marks at the top of the strip to show that this is the ink from the person believed to be the marshmallow criminal.


4. Finish The Strips

Write the numbers "1" to "4" at one end of each blank strip of filter paper.   Make a line on strip #1 using marker #1;  draw the line about 1" from the end of the strip.  Do the same for strip #2 and marker #2 and so on for all of the markers.


5. Prepare a Beaker.

Obtain a clear plastic or glass cup or container.  Put in only enough water to make the water about 1/4" deep in the bottom.


6. Add The Strips.

Now add the strips with the ink mark down. Put the strips in just far enough so that the water just touches the paper. Don't put the strip in so far that the ink mark is under water. When each strip is just right, fold the strip over the side of the cup to keep the strip in place.


7. Check The Results.

Wait several minutes for the water and ink to diffuse, Then take out the strips and compare the results with the unknown. Who is the marshmallow criminal? The ink found at the supermarket is on the first strip, and the marker belonging to suspect number 3 (Fearless Leader) was used to make the strip second from the right.


What's Going On?

Colors separate out of the black ink mark from a marking pen line on a coffee filter. As water seeps up the filter paper, the molecules of color are carried with them. They can be separated because they are in a mixture rather than being chemically combined. They will attach themselves to the cellulose in the paper, but with differing affinities depending on their chemical nature. Some cling hard, others are only weakly held. Those that are weakly attached to the cellulose travel further up the paper than those with the stronger bond, and they will spread further. Components in similar chemical tests, such as DNA segments in gel electrophoresis, can be identified by how far they are carried.


Credits

Images of Boris Badenov, Natasia Fatale, Fearless Leader and Rocket J. Squirrel: © Jay Ward Productions.