Carnegie Mellon University


Hunter Scientific Company has reported the theft of one of its famous works of art from the Middle Ages.

The painting "The Alchemist's Wife at Work in Her Home Laboratory" was stolen from the main reception room after normal working hours. Security cameras mounted in the area were somehow temporarily disabled and the thief got away.

The next day, a laboratory technician found a ransom note, signed in black ink, on the lab bench top.  The technician was able to pin-point the time when the note was placed there to between 10:05 AM when she started an experiment, and 10:25 AM when she noticed the ransom note.

Hunter Scientific security cameras showed that only three people entered the research corridor during that time period; Joe Beakerman, April Burette, and Jason Bunsen.

Police searched the offices of all three employees and confiscated a black pen in each.  The artwork was not found. Determine which pen signed the ransom note and identify the thief.

Scientific Information

CHROMATOGRAPHY is an ancient technique that separates a substance from within a mixture.  It is widely used in research and industry to separate and identify the components of mixtures.  Examples include finding pollutants in water and soil and studying the ingredients in food and cosmetics.

Ink is made up of a mixture of colored pigments which when blended together give it a particular color.  We can separate the pigments using a technique called PAPER CHROMATOGRAPHY.

A spot of ink is placed on some chromatography paper and a liquid is allowed to slowly travel across the paper.  As it travels, some of the components of the mixture travel with it.  The ones that are most easily dissolved in the liquid travel the farthest.  A characteristic pattern forms called a chromatogram.

Ink in a particular pen can be identified by the colors it separates into and their positions on the chromatogram.  We will make chromatograms of all three pens confiscated by the police and of a sample portion of the ransom note.  By comparing the ransom note's chromatogram to those of the three pens, we can determine which pen may have written the note.