Determination of caffeine in green tea by extraction with ethanol

Caffeine is a substance occuring in many beverages – especially known in coffee and black tea but also in soft drinks as Coca Cola. With around 120,000 t/a caffeine is the world´s most popular psychoactive substance. Caffeine is a stimulant for the central nervous system and increases focus, body coordination and the person´s awakeness. Effects show rather fast (below one hour). The duration of the listed positive effects disappear after a few hours – the half-life of caffeine in a person is around five hours. Too much caffeine input is not advisable for the human health, an uptake below around 250 mg/d should not lead to concerning negative health effects. Concentrations above 250 mg/d though, can lead to caffeinism which expresses itself by nervousness, irritability, restlessness, insomnia, headaches and heart palpitations. Determination of caffeine concentrations in beverages usually needs a time-consuming sample preparation with several steps for separation of unwanted substances and extraction steps for concentration of the caffeine. But also the total amount of caffeine in the dried tea before decoction is of interest. On the one hand to see differences in species and origin, and on the other hand to calculate the extraction yield during the decoction process. In this investigation green tea powder taken from tea-bags has been directly extracted with ethanol. Amounts of tea dry mass (100 – 250 mg) and extraction volume (5 – 20 mL) have been varied in order to investigate possible effects and to optimize the method. Best results were found for using 10 mL ethanol for 100 mg sample. The method optimized was used for the analysis of commercially available green teas. Furthermore tea infusions have been prepared as usually with hot water using the optimal extraction time given on the tea packages as basis for extraction yield determinations All samples have than been measured at room temperature with HPLC. The caffeine content has then been determined at 273 nm.