Paper Chromatography: Separation and

The example of column chromatography (Figure 1) demonstrates the typical features found in this analytical technique. The diagram shows an experiment where a two-component mixture is subjected to column chromatography. The column is packed with a solid material called the stationary phase. A liquid solvent or eluting solution is poured into the column and completely wets the solid packing material. Then the mixture is loaded onto the top of the wet column and more eluent is added. Gravity pulls the mobile phase down through the stationary phase and the components in the mixture start to move through the column at different rates. In the diagram, component A moves faster than component B; thus component B is retained on the column for a longer time than component A. Usually this is due to a difference in solubility of the two compounds in the solvent and/or to a difference in attraction to the solid packing material. As more eluent is added to the top of the column, the components will eventually exit the column separately. The time taken to exit the column, called retention time, will be reproducible for each component under the given set conditions—mobile and stationary phase identities, temperature and column width. Once the components exit the column, the solvent can be removed by evaporation and the pure components can be further analyzed or identified.