Tuesday: Mock CSI Crime – Chromatography

Welcome to Day 2 where your STEM Explorer solved a CSI Mock Crime using Forensic Science.

Chromatograohy
Today we were detectives and used paper chromatography to figure out which of five different black pens was used to write the letter left at the crime scene. Paper chromatography is a separation technique in which dots of pigment, in our case ink, are placed on special filter paper and the paper is then dipped into a solvent. We used 70% rubbing alcohol as the solvent, and as the alcohol traveled up the paper, it dissolved the dots of ink and carried them along with it. Since black ink is actually a mixture of several different colors, or pigments, the colors get spread out on the paper because they have different affinities to the paper. At the end of the experiment, we took the papers out of the alcohol and these were our chromatographs.
We then were able to compare our chromatographs to the “unknown” chromatograph to figure out which pen was used to write the letter.

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