The project I performed was Paper Chromatography. In this project I attempted to separate different colored dies from the ink in marking pens. I used purple, yellow, black, blue and green Sharpie pens, a green Marks-a-lot and black and green Secureline lab markers. In some cases the ink from these pens separated into various colored dies used to create the color of an ink in a pen. I used Hexane, Rubbing Alcohol and Toluene as solvents to separate the dies from the inks. In the experiment I performed I found out how pure the inks being used today are compared to the combination of dies used in the past to create a colored ink. The pens I used contained dies that were for the most part pure pigments. I only had a few examples of inks that contained more than one color of die.
Paper Chromatography was discovered in 1903 by a Russian botanist by the name of M.S. Tsewtt. By studying the coloring material in plants Tswett developed a way to seperate the different colors that make up the overall color in plants. After the discovery of paper chromatography it was not popular nor widely used until the 1930's. Since the 1930's paper chromatography has been used by people in many different professions from the FBI to medical scientists. In general the process of paper chromatography is used by scientists for separating organic and inorganic compounds. By doing this scientists can determine the purity of a compund and what the make up of the compound is.
In chromatography, substances travel between a stationary phase and a mobile phase. In paper chromatography the stationary phase is the chromatography paper. The mobile phase is the solvent moving up the chromatography paper carrying the samples, or dies, with it. Components, or dies, in the ink will separate onto the chromatography paper, or stationary phase. The dies will separate depending on how strongly they absorb into the paper versus how much they dissolve in the mobile phase or solvent. The process of dies or solutes separating and sticking to the paper, or stationary phase, is called Chromatographic Development.
1. The first thing I did was gather an assortment of pens from around woods labratory. I picked up some dry erase pens, Sharpies, a Marks-a-lot and Secureline lab markers. In the end I only used the sharpies and the secureline lab markers because the dry erase ink would not separate in any of the solvents I used.
2. Secondly I picked up some chromatography paper and cut it into strips six inches long and 2cm wide. I cut approximately 20 strips but I ended up using only 13.
3. In pencil I drew a line 2cm from the bottom of the chromatography paper. In the middle of this line is where I placed the dot of ink from the pens. On some strips of paper I used a higher concentration of ink by repeatedly dotting the area of with the pen.
4. The next thing I did was to get some test tubes and cork stoppers. I put approximately 3mL of solvent in the test tubes.
5. I placed each strip of chromatography paper into a test tube, allowing the solvent to touch the end of the paper but not the ink itself. I did this by placing the paper inbetween the cork stopper and test tube.
6. The solvent moved up the paper carrying the separated ink with it. As the ink traveled up the paper, dies within the ink began to separate. Only a few of the inks I used separated out into different colored dies. The majority of the inks simply traveled up the paper in the solvent without separating.
7. I repeated steps five and six with each of the solvents (Hexane, Rubbing Alcohol and Toluene).
Observations and Data
The results from my chromatography experiment are as follows:
As you can see, out of all three solvents used, rubbing alcohol carried the inks the farthest up the chromatography paper and was most effective at separating them. The red Sharpie and the green Marks-a-lot were the only the markers with inks that separated. These two inks were the only ones that contained more than one color of die.
The other colored markers contained pure pigments in their dies. This can be seen because of the lack of other colored dies on the chromatography strip.
The image above shows a paper chromatography test done with various colored inks. This example is very clear, showing how the dies move up the paper.
In paper chromatogrpahy certain calculations can be done to identifiy substances within a compund. The Rf or retention value of a substance is what is used to help identify those certain substances. The Rf value is found by dividing the distance from the start to the center of the the substance by the solvent front. The solvent front is how far the solvent traveled up the paper from the start and can be seen on the image above.
My results from this experiment were somewhat pleasing but for the most part frustrating. I had hoped to get more separation of dies in the inks I used but because of how pure the pigments were, that were in the inks, made it impossible for any dies to separate out of the inks. Although only the red Sharpie and green Marks-a-lot markers separated, it is clear that Paper Chromatography is a good and effective way to identify substances within a compund.
Block, Richard J., Emmett L. Durrim, Gunter Zweig. Paper Chromatography and Paper Electrophoresis, New York, New York, 1958
I would like to thank the staff in the computer lab for their help with this project. I am not very computer literate and I had a lot of touble inserting images onto this website.