The distribution coefficient for caffeine in dichloromethane and water
is 4.6. Assume that your 100-mL tea solution contained 0.3 g of
caffeine. If you had only extracted with one 15-mL portion of
dichloromethane, how much caffeine would have been left in the
water solution? How much would be left in the water after the second
15-mL dichloromethane extraction? How much caffeine would be left
in the water solution if only one extraction with 30 mL of
dichloromethane were performed?
5. Why is less caffeine actually isolated than is suggested by the
calculation in Question 4?

Introduction Caffeine is one of three legal, mind-altering drugs available in the U.S without a prescription. Two common sources of this drug are tea and coffee, both of which are prepared via extraction of the solid foodstuff with liquid water. In this lab you will extract caffeine from food samples with liquid solvents and quantify the amount obtained. Laborator Hypothesis: We can rank various tea and coffee samples by caffeine content by performing a solid-liquid extraction from the foodstuff, followed by analysis via thin-layer chromatography. Experiment: In a 50 mL Erlenmeyer flask were placed 2.0 g of black tea. Dichloromethane (15 mL) and 0.2 M NaOH (5 mL) were added successively, and the stoppered flask was swirled gently by hand for 10 minutes (note: avoid vigorous shaking, as it will cause an emulsion to form). The dicloromethane layer was separated from the leaves and the aqueous layer by vacuum filtration through 7 g Celite 545, and the leaves were washed with a further 15 mL dichloromethane. The combined dichloromethane solution was placed in a 50 mL round bottom flask and concentrated to a minimal volume (ca. 1 mL) via simple distillation. The remaining dichloromethane solutions was transferred to a watch glass via pipet, and the solvent was evaporated in a fume hood. The sample was evaluated by TLC (a mixture of methanol and ethyl acetate as the mobile phase, co-spotted with authentic caffeine). Data: What was your crude yield of caffeine? What was the mass percentage of caffeine in your food source'? Given that the materials we are interested in are UV active, compared to the TLC standard how would you characterize the purity of your caffeine extracts? Conclusions: Can you comment on the purity of your caffeine sample? For all samples your class worked with where does your foodstuff rank in terms of caffeine content? How much caffeine is reported for the typical serving of coffee or tea? How did your extraction and isolation compare with the typical serving?

Introduction Caffeine is one of three legal, mind-altering drugs available in the U.S without a prescription. Two common sources of this drug are tea and coffee, both of which are prepared via extraction of the solid foodstuff with liquid water. In this lab you will extract caffeine from food samples with liquid solvents and quantify the amount obtained. Laborator Hypothesis: We can rank various tea and coffee samples by caffeine content by performing a solid-liquid extraction from the foodstuff, followed by analysis via thin-layer chromatography. Experiment: In a 50 mL Erlenmeyer flask were placed 2.0 g of black tea. Dichloromethane (15 mL) and 0.2 M NaOH (5 mL) were added successively, and the stoppered flask was swirled gently by hand for 10 minutes (note: avoid vigorous shaking, as it will cause an emulsion to form). The dicloromethane layer was separated from the leaves and the aqueous layer by vacuum filtration through 7 g Celite 545, and the leaves were washed with a further 15 mL dichloromethane. The combined dichloromethane solution was placed in a 50 mL round bottom flask and concentrated to a minimal volume (ca. 1 mL) via simple distillation. The remaining dichloromethane solutions was transferred to a watch glass via pipet, and the solvent was evaporated in a fume hood. The sample was evaluated by TLC (a mixture of methanol and ethyl acetate as the mobile phase, co-spotted with authentic caffeine). Data: What was your crude yield of caffeine? What was the mass percentage of caffeine in your food source'? Given that the materials we are interested in are UV active, compared to the TLC standard how would you characterize the purity of your caffeine extracts? Conclusions: Can you comment on the purity of your caffeine sample? For all samples your class worked with where does your foodstuff rank in terms of caffeine content? How much caffeine is reported for the typical serving of coffee or tea? How did your extraction and isolation compare with the typical serving?