In this research, characterization of pure caffeine and the method for determination of caffeine content in twelve commercial tea leaves have been reported using UV-visible spectrometer. The optical transition properties of caffeine were measured in different solvents (dichloromethane, water, chloroform and ethyl acetate). The results show that, caffeine has highest optical transitions in dichloromethane than the other solvents. After characterization of the electron transition, the content of caffeine in 6 Ethiopian black and green tea leaves and 5 different black tea leaves from South Africa, Kenya, 2 India, Zimbabwe, and Sri Lanka green teas, were analyzed at 30°C. Four Ethiopian tea samples were also analyzed at the boiling temperature using smaller extraction time. The result of the experiment at both temperatures indicates that, the caffeine content of Ethiopian green tea leaves is greatest of all the Ethiopian teas while black lion tea has the least. Of all the samples tested, Kenyan black tea had the highest caffeine content and Sri Lankan green teas had the least caffeine. The result also indicates that, caffeine can be extracted more at the boiling temperature than at 30°C. Furthermore, the absorption range of cinnamon tea was greater than the others by 16 nm.
Key words: Tea leaves, caffeine, extraction, UV-visible spectrometer, optical transition properties.
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