SAFETY NOTES: The solvent used in the chromatography tank generates significant fumes that can be corrosive to contact len material. No contacts should be worn during this lab experiment. Persons with asthma should notify their TA so that they can work at the hood to avoid any irritation that the fumes might cause.
GENERAL INSTRUCTIONS: Each student will generate their own chromatogram.
| Part I: Preparing the Chromatography Tank | |
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Prepare the chromatography tank by pouring 40 mL of the solvent mixture (3:2 ethanol/water) into a clean 1000 mL beaker. Cover the top of the beaker with Saran Wrap securely to allow the solvent to saturate the air in the beaker with solvent vapor. |
| Part II: Preparing the Chromatogram | |
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Obtain from the instructor a pre-cut 11 x 20 cm sheet of chromatography paper. The width of the paper should be a little less than the depth of the chromatographic tank and the length should allow the formation of a cylinder that will fit into the tank with adequate clearance from the sides. Avoid contamination of the paper by handling it only along the narrow ends, and use a sheet of clean paper to protect it from the bench. |
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Make a pencil line across one side 1.5 cm from the edge. In increments of 1.5 cm, mark off the line using a pencil. Label the marks in pencil with abbreviations of the color standards and M&M colors that will be used. See Figure 1 for clarification. |
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Spotting requires practice and patience. Obtain several toothpicks from the front counter. Using your large watch glass, place a drop of one of the food colors in the center of the glass. Use one of the toothpicks, to practice making several spots on a scrap of filter paper. The spots should be no more than 2 mm in diameter. When you are confident you can make good spots, continue on to step 5. |
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Carefully apply the four food colorings to your chromatography paper. Allow the spots to dry completely. |
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Obtain 1 M&M of each color from the front counter. |
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Dip a toothpick in DI water to moisten the tip and then rub it on one of the M&Ms until you see enough color transfer to spot the chromatography paper. Spot the paper as before. You may need to make several transfers to the same spot so that it is as dark as the standard food color spots. Repeat the process until each M&M color has a spot. (Return the used M&M's to the front counter for others to use) |
| Part III: Running the Chromatogram | |
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Coil the chromatography paper into a cylinder and fasten with three staples, making sure that the stapled ends do not touch or overlap as touching ends will cause an uneven flow of solvent up the paper. |
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Insert the cylinder into the beaker. Cover the beaker with the Saran wrap during the development. Record the time when development started. Make sure your set-up looks like the one pictured here. |
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Allow the beaker to remain undisturbed for one hour. |
| Part IV: Removing the Chromatogram | |
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At the end of one hour, the solvent front should be about 2 cm from the top of the upper edge of the cylinder. Remove the cylinder and immediately mark the position of the solvent front with a pencil line. Allow the cylinder to dry standing on a clean piece of paper. |
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When dry, remove the staples, flatten the cylinder out and examine the chromatogram. Measure and record the distance each component in the food colorings traveled from the original spot 1.5 cm from the bottom. Record the distance the solvent front traveled beginning at the line 1.5 cm from the bottom. |
