The purpose of paper chromatography is to separate a mixture into its various components. Using a sample that is a mixture of several highly colored components, such as ink or leaf pigments, allows the scientist to see the components as they separate. With samples that do not display colors, other means of detection are necessary.
The idea behind chromatography is that different chemicals will move through different substrates at different rates. Therefore, if the column is long enough, the different substances can be separated, either for fractioning or for analysis. While scientists use advanced types of chromatography with specialized equipment, similar processes allow junior scientists to experiment at home. Coffee filters cut into strips make an ideal medium for practicing chromatography skills. About.com suggests using white chalk as the medium for separating ink or food coloring into various components using rubbing alcohol as a solvent. Once the chalk dries, it writes with the different colors.
Paper chromatography allows the user to place a spot of a known substance beside an unknown in order to determine if the two are the same by the ways the colors separate. In a similar way, chromatography finds use in many different fields, including medical testing, scientific research, chemical analysis and industry.