A large number of dietary supplements and beverages containing caffeine are available on the market. Caffeine is a natural alkaloid found in leaves, fruits and seeds of many plants. People like to drink caffeine because of its stimulating effect, which reduces exhaustion and sleepiness. In this diploma thesis I aimed to determine the caffeine content in various dietary supplements and drinks (coffee and tea). A reversed-phase high performance liquid chromatography with UV detector was used for determination of caffeine. I also checked repeatability of the chromatographic method. I came to conclusion that Guarana natural energy supplement contains the most caffeine, while green tea turned out to be the least caffeinated.
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