Student understanding of chromatography: a hands-on approach

Chemistry students are better prepared for careers if they learn about the principles of polarity and chemical partitioning that underlie various kinds of chromatography. Principles are more or less the same for paper chromatography, high-pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC). In science education hands-on activities should illustrate principles. Plant materials, especially colorful leaves such as those of Coleus plants or fall leaves which had been green and then became red, can be used. In a Coleus leaf the pigments represent molecules with a wide range of polarities. First students see a demonstration that results in partitioning of pigments. Later they use their understanding to develop a system to separate different pigments using a rather inexpensive TLC system. They make their own developing solutions. Even advanced high school chemistry students can profit from these activities. The kind of polarity involved with chromatography is not the same kind generally referred to in organic chemistry classes. A football game/music analogy is suggested to help students understand partitioning.