Paper Chromatography Experiments

A method of analyzing compound mixtures like ink through a process of separating them into the chemicals that are used to make them is called chromatography and is even used identify drugs that could be in samples of urine and blood. What happens is essentially the result of separation of the compounds because of their different molecular sizes.

If you take several coffee filters and cut them into long strips, fold one end into a loop and glue or staple the loop. The loop must be large enough that you can get a pencil through the loop. The strip of the coffee filter should be long enough to reach near the bottom of a drinking glass and all the strips you make should be the same length and the glasses you use should be the same size. You will measure up from the bottom of the strips of paper about 1 1/2 inches and make a small but visible mark with a Pencil. Then at the point of the mark you would make a small dot of ink with an ink pen. On each strip you would make a similar sized dot of ink with a different kind of ink and/or a different color (water soluble) ink. You would add water to the glasses to a level that would allow the bottom of the strips to get into the water but not touching the dot of ink. All the water levels should be the same. You would put the pencil through the loop and then let the strip of coffee filter paper with the ink dot go down into the glass and into the water. As the water travels up the paper strip it will come into contact with the ink and as it moves more up the coffee filter it will carry the lighter ink particles quicker and further up the paper strip. The heavier molecules in the ink will travel slower and not as far up the filter paper. Each kind of ink will create a different pattern of ink separation. Other types of inks will most likely need a different solvent like rubbing alcohol. Other substances may pose fire or health hazards so for children it is usually better to use water as the solvent and water soluble inks to test. You can also test other substances through this process but inks provide a nice very visible separation pattern.

Television shows about crime scene investigation have shown this process but use more sophisticated methods of separation. By comparison with known data investigators can gain a lot of information that might not have been previously available. Substances can also be burned and the light produced can be viewed through a spectroscope. In a way this seems like a similar type of investigation. The spectroscope separates the light into different bands of colors. The spectroscope does not use a solvent however and sometimes people confuse the two different processes.