Column Chromatography: Isolation of Lycopene from Tomato Paste
Reading: Zubrick, pages 79-82, 127-130, 138-139, 141-143, and 235-240
Pre-lab: look up the structure of lycopene.
Introduction: Lycopene is the red pigment in ripe tomatoes and, as an antioxidant, helps to fight certain cancers. In this lab you will isolate lycopene from tomato paste. To do this you will first extract carotenoid pigments from the paste and then use column chromatography to isolate the lycopene from the other pigments. You will then use TLC to evaluate the column chromatography separation. Note: because lycopene is light-sensitive, prevent any unnecessary exposure to light.
Weigh roughly 1.0 g of tomato paste into a 15 mL centrifuge tube. Add 4 mL of a 50/50 (% volume) mixture of petroleum ether and acetone. Cap the centrifuge tube and shake until the solid becomes fluffy. Open the cap and crush the solid with a spatula. Close the tube and shake again. Repeat this crushing and shaking two more times. Centrifuge the tube to separate the extract and residue. Remember to balance the centrifuge so that it does not walk (perhaps you and your neighboring lab group can share and balance each other’s tubes) and do not stop the centrifuge with your fingers! Transfer the extract (liquid) to a clean centrifuge tube. In the original centrifuge tube, add a new 4 mL of solvent and repeat the entire extraction procedure. Add the resulting extract to the first extract (in the second centrifuge tube). Now wash (microscale) the combined extracts with saturated NaCl solution (5mL), then with 10% aqueous potassium carbonate (5mL), then with saturated NaCl solution (5 mL) again. Dry the organic layer with anhydrous sodium sulfate. Decant the organic layer into a small beaker and concentrate to roughly 0.2 mL by evaporation in the hood (do not apply heat!). If the sample goes to dryness, re-dissolve in hexane (0.2 mL).
*Set aside a small amount of your crude