During photosynthesis, molecules referred to as pigments (due to the wavelength, thus color, they reflect) are used to capture light energy. Four primary pigments of green plants can easily be separated and identified using a technique called paper chromatography.

The process of chromatography separates molecules because of the different solubilities of the molecules in a selected solvent. The solvent carries the dissolved pigments as it moves up the paper. The pigments are carried at different rates because they are not equally soluble.

In Autumn, chlorophyll breaks down, allowing xanthophyll and carotene, and newly made anthocyanin, to show their colors. The mix of pigments in a leaf may be separated into bands of color by the technique of paper chromatography. Pigments are separated on the paper and show up as colored streaks.

From this, we can deduce that carotenes are the least polar pigments (no polar groups), and xanthophylls are the most polar (two alcohol groups, one at each end of the molecule).

The Rf values indicate how soluble the particular pigment is in the solvent by how high the pigment moves on the paper. Two pigments with the same Rf value are likely to be identical molecules. Small Rf values tend to indicate larger, less soluble pigments while the highly soluble pigments have an Rf value near to one.

However, because Rf values are relative, not absolute, some compounds may have very similar Rf values. It is primarily used to determine the purity of a compound. A pure solid will show only one spot on a developed TLC plate.

Radio frequency (RF) is a measurement representing the oscillation rate of electromagnetic radiation spectrum, or electromagnetic radio waves, from frequencies ranging from 300 gigahertz (GHz) to as low as 9 kilohertz (kHz).