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Determination of Caffeine in Tea: A K11-12 Project

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Tea leaves from different sources taken in individual beakers

Tea leaves from different sources taken in individual beakers

Tea decoction filtered

Tea decoction filtered

Tea decoction treated with lead acetate

Tea decoction treated with lead acetate

The tradition of tea drinking is ritualistically observed in almost all countries around the globe. The student community patronizes tea drinking as the caffeine kick is important. It helps meet time targeted deadlines and fight jet lag to make timely submissions.

The analysis of caffeine becomes pertinent when overuse of caffeine leads to its manifestation on the physical body in the form of insomnia, nausea, tremors ,vomiting, chest pain and palpitations which pose a serious health hazard. Caffeine is instrumental in triggering panic attacks as well as interfering with sleep patterns. Caffeine interferes with the absorption of calcium , thus increasing the risk of osteoporosis.

The caffeine content in a cup of tea depends on the dry weight of the tea, the type of tea, as well as the method used to brew the tea. On an average there are 30-90 mg of caffeine per cup of tea. The astringency in tea can be attributed to the presence of poly-phenols. These are the most abundant compounds in tea leaves, making upto 30-40% of their composition. Tea also contains small amounts of theobromine and theophylline, which are stimulants, along with xanthines which have structures similar to caffeine. The decoction prepared from tea leaves has properties of both a solution as well as a suspension. It is a solution of all the water-soluble compounds that have been extracted from the tea leaves, such as the polyphenols and amino acids, but it is a suspension when all of the insoluble components are considered, such as the cellulose in the tea leaves.

Caffeine is a central nervous system (CNS) stimulant of the methyl-xanthine class.It is the world's most widely consumed psychoactive drug which is legal and unregulated in all parts of the world. There are several known mechanisms of action to explain the effects of caffeine. The most prominent is that it reversibly blocks the action of adenosine on its receptor and consequently prevents the onset of drowsiness induced by adenosine. Caffeine also stimulates certain portions of the autonomic nervous system.

The tea extract is treated with lead acetate. The tea leaves in the presence of water dissolves many glycoside compounds in addition to caffeine. The clear solution is then treated with lead acetate to precipitate the glycoside compounds in the form of lead complex.
The solubility of caffeine in chloroform is quite high at room temperature. Therefore, when chloroform is added to the aqueous caffeine solution, the caffeine is transferred to the chloroform. The chloroform- caffeine mixture can then be separated by utilizing the different densities of chloroform and water. Because chloroform is much denser than water and insoluble in it, the chloroform will form a layer under the water and can be separated. Ten grams of the tea sample is taken in a beaker to which 100 ml of water is added. The tea –water solution is placed over the bunsen burner, until the solution begins to boil. The solution is then filtered through a filter paper. The liquid obtained in the new beaker is the filtrate. To which lead acetate is added. The solution is filtered with the formation of a slightly colored liquid. This solution is heated and reduced to half its original volume. This reduced volume solution is allowed to cool in a beaker after which 10 ml of chloroform is added. A separating funnel is taken and washed with water and then rinsed with chloroform. The solution from the beaker is now added to the separating funnel. Here it is allowed to separate out in the form of layers. A stopper is placed on the separating funnel and then solution is thoroughly swirled. The solution is allowed to separate out again. A weighed beaker is placed below the separating funnel and the lower layer is separated out.

  1. The beaker is now placed into a hot water bath so that the chloroform is evaporated.
  2. The residue left behind is the caffeine present in the sample.
  3. The beaker is allowed to cool.
  4. The beaker is now weighed and the observations are recorded.

The same procedure is repeated for the remaining three tea samples.

The experimental work for the above project was completed by Aarushi Kataria and Vaishnavi Vishwanath of R.N Podar Sr. Sec High School under the guidance of Ms Anjali B Gharpure