Chromatography is one tool scientists use to separate mixtures of substances. We used one of the simplest, paper chromatography, to explore the composition of inks. Students applied inks to strips of heavy paper, then observed the various components move as water traveled up the paper.
We compared the behavior of six different black pens, Sharpie, Alvin Penstix, Flair, Expo Wet Erase, Crayola Washable, and EF Felt Tip in six different solvents, water, rubbing alcohol (70% isopropyl alcohol 30% water). ethanol, methanol. methyl ethyl ketone, and dichloromethane. Students determined how many dyes made up each black ink, and calculated retention factors for several of those dyes.
Students received pairs of paper strips, each with a dot of the same unknown ink. They put drops of water on one dot, rubbing alcohol on the other. After waiting one minute, they tried to identify which of 60 possible inks their sample represented.