Chromatography is an analytical method used to separate a mixture of compounds, for instance, to identify individual colored pigments found in photosynthetic samples.
In one variant—liquid chromatography—the solid pigments of interest are first dissolved in a liquid and applied to the bottom edge of the stationary phase—an adsorbant material like filter paper. The spotted paper is then placed into the solvent. Flow is created by capillary action as the solvent carries the components up—referred to as the mobile phase.
Based on differences in physical properties, like interaction strength and solubility, pigments will either more strongly adsorb onto the filter paper or more readily dissolve in the solvent. Thus, distinct molecules will leave the solution at different rates as the solvent continues to travel up. The relative distance travelled by each pigment can be divided by that of the solvent, providing the retention factor, or Rf, which can be compared to known values for final identification.