Determination of caffeine
1 g solid sample (or 200 mL liquid sample) was taken in 750 mL Erlenmeyer beaker
and subsequently distilled water (450 mL) was added to it. To remove tannins 50 mL
H2SO4 0.1N were added to the sample. The mixture was boiled for 30 min and filtered
through filter paper. Then 7 mL Zn(CH3COO)2 1M and 6 mL K4[Fe(CN)6] 0.25 M was
added to 50 mL of the filtrate in a 100 mL volumetric flask. After the volume was
adjusted to the mark, the solution containing zinc precipitate was filtered. Absorbance
of this filtrate was measured at 273.5 nm.