Tonya Wright 01/02/98
Many water-soluble dyes can be easily separated on paper. Artist's watercolor paper works well (make sure the paper is white). "Spot" the paper by applying the pigment with a capillary tip; if you can let the spot dry completely and then reapply pigment in exactly the same place you'll get better results. Place a concentrated (e. g. 20% w/w) NaCl solution in a glass or beaker and suspend the paper vertically so the edge below the spot is soaking the solution. Keep the top of the container closed so the paper can't dry out as the solvent front rises.
- The solvent front may be uneven if the chamber isn't saturated with solvent vapor.
- If you don't get a good separation try diluting the salt solution until you do.
- If the separation is still poor or the spot doesn't move much, try mixing a little alcohol in with the solution.
- If you see a lot of "tailing", you might try adding some acetic acid or vinegar to the solution. The tails are often caused when the dye is a weak acid or base present in several different ionic forms; adding vinegar helps to keep the dye a single (acid) form.
The following Web sites contain useful background information and experimental procedures for paper chromatography.
Analysis of Mr. Sketch Ink by Paper Chromatography
The St. Louis Chromatography Discussion Group 
A laboratory exercise that includes a nice introduction to color mixing and paper chromatography.
http://wwwchem.csustan.edu/chem1002/mrsketch.htm (01/02/99)This site is for professional chromatographers, but it includes a discussion board with friendly answers for high school, science fair, and college level questions.
http://www.stlcdg.org/ (01/02/99)