PURPOSETea is a beverage which is consumed all over the world. One of the main reasons for this consumption is that tea contains caffeine. Caffeine is alkaloid compound, which like other alkaloids, such as ephedrine, is a natural stimulant. All types of tea (green, oolong and black) are all produced from the same leaves; however the processing method is different. When wanting to extract caffeine from tea, it can be difficult due to the other cellular components. Besides caffeine, tea leaves also contain cellulose, proteins, amino acids, tannins, pigments and saponins. Here we will extract only caffeine from tea by using a variety of different chemicals to ensure that all other components are removed from the solution and only the caffeine remains.
One tea bag was weighed and placed in a 250ml flask with approximately 0.3g of sodium carbonate and 100ml of water with a boiling chip. The Sodium carbonate was added to ensure that caffeine remained present as a free base. This solution was then boiled for 20 minutes with gentle stirring. Then the bag was squeezed against the sides of the beaker with a glass rob to maximize removal of tea solution, and then thrown away. Then 1ml of a saturated sodium chloride solution was added to the flask. The sodium chloride makes the water in the solution be more attracted to the polar sodium chloride, then the caffeine allowing it to be extracted into the organic layer. The solution was then extracted with 25ml ethyl acetate and transferred to a 100ml graduated cylinder and the top layer was placed in a 125ml erlenmeyer flask. This was repeated one more time and the second organic layer was combined with the first organic layer. The organic layer was then dried using anhydrous sodium sulfate, to remove any remaining water, until it was clear. The dry layer was then removed and placed into a pre-weighed 125ml flask. The solution was then heated until 1ml remained and then left to evaporate. The flask was then reweighed to determine the weight of the crude caffeine extract.
The extract was dissolved in 1ml ethyl acetate and, using a capillary tube, one drop was placed on the start line of a prepared TLC plate. The plate was then placed into a 200ml beaker with 10ml developing solution, composed of 75% ethyl acetate and 25% hexane. This was covered in plastic wrap and left until the solvent migrated to the top of the plate, then a line was drawn to mark the solvent front. The plate was then dried and under UV light the spots were circled and measured.
In total 2.5688g of tea was used. The empty flask weighed 63.11g and with the crude caffeine the weight was 63.27g. On the TLC front the caffiene spot migrated 3cm and the solvent front migrated 6.2cm.
The weight of the crude caffeine extract was 0.16G (63.27g – 63.11g). This means taht the approximate percent caffeine in tea was 6.22% [(0.16g/2.5688g)*100%]. On the TLC plate the Rf value was 0.48 (3cm/6.2). Pure caffeine has an Rf value of 0.12, therefore the crude extract is not pure and contains contaminants.
Overall it was determined that the percent caffeine of the tea bag was approximately 6.22%. However, when run on a TLC plate, an Rf value of 0.48 was obtained indicating that the extract was not pure. Therefore, this is a source of error for the calculation of percent caffeine, due to the presence of contaminants which will inflate the percentage. In future if repeated, attempts to remove these contaminants should be preformed to better determine the actual percentage of caffeine.