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Thursday, October 20, 2005
 
::FUN CHEMISTRY FACT OF THE DAY, PART 5::

On with my affinity for the chemistry of color and light!

Chromatography involves the separation of complex mixtures. Ecologists perform chromatograms on air samples to see what gases make them up. Detectives (chemical detectives!) use chromatography to match pen types used in ransom notes. The funnest (and most see-it-yourself) version uses paper or fibrous material to "seep" various colors of ink from a pen.

Imagine you're using a black felt-tip pen to write a note. You're actually using about four colors blended together. By using chromatography (chroma = color; graphy = representation), you can get the inks, due to "the differential affinities of substances for a stationary adsorbing medium through which they pass" (basically, how "willing" they are to seep through a piece of filter paper), to make a little rainbow "fingerprint" exclusive to that pen. Try it!

What do you think would happen if you used a Sharpie (or other permanent marker) in that experiment?

(Chromatographic answer in the comments.)
Comments:
It wouldn't work -- you'd need to use alcohol.

Since water is polar (has different electrochemical charges on each end of the molecule) and non-permanent marker ink uses polar molecules, too, they form intermolecular bonds, and the water "seeps" and dissipates the ink just fine. Polar water, though, doesn't have any "pull" with Sharpie ink, which isn't polar.

The non-polar job is done by alcohol, though, so if you label stuff with a Sharpie and get alcohol in it (when would that ever happen, hmmm?), you're totally (though beautifully chromatographically) screwed.
 

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