BIOC 2580 Lecture Notes - Lecture 21: Glyceraldehyde, Stereoisomerism, Asymmetric Carbon

Thin Layer and Paper Chromatography hromatography is a method of separation of compounds based on the principle of phase distribution. There are several different kinds of chro matography: thin layer, gas, paper, column and liquid chromatography are among the most common types used in organic chemistry. All methods of chromatography involve the partitioning of a substance between a stationary phase and a mobile phase. In paper chromatography the paper itself serves Background and Theory as the stationary phase and the eluting sol as the mobil phase. In layer chromatography the stationary phase is the silica gel layer, a plastic or glass plate scrves as a support, while again the eluting solvent functions as a mobile phase. The stationary phase adsorbs compounds by molecular interactions between functional groups on the stationary phase and the analyte compound. The commonly used stationary phases are polar. Thus, in this type of chroma- tography polar compounds are held more strongly by the stationary phase. Therefore, in order to elute increasingly polar compounds a mobile phase of greater polarity is needed. This property defines an eluatropic series. It begins with nonpolar solvents and proceeds gradually to the mostp organic solvent, methanol and finally water. The ability of a solvent to elute a given substrate from a stationary phase depends on the solvents eluting power and thus its polarity olar

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?