Experiment two: Extraction of caffeine from tea by Soxhlet technique and purity analysis using high performance liquid chromatography (HPLC).
Introduction:.
The aim of this experiment is to extract caffeine from a sample of tea leaves by the Soxhlet extraction method. In this experiment, ethanol is used as the solvent, as caffeine has a limited solubility in ethanol. The ethanol is boiled, and the vapours are condensed, which fall down into a thimble containing the tea leaves. The required caffeine in the tea leaves is partially dissolved in the solvent and then extracted from the tea leaves into the solvent. This process is repeated, and the tea leaves which can't dissolve in the solvent are left in the thimble. The advantage of this process is the same solvent is recycled during the whole process.
The purity of the sample is then analysed through HPLC. The mobile phase in this experiment consists of a mixture of methanol and water, the ratio of which is determined by the separating abilities in relation to a 50/50 caffeine theopylline mixture. Using solutions of varying concentrations of caffeine and constant concentrations of theophylline, a calibration curve is constructed. The desired sample with unknown concentration of caffeine is then analysed and found from the calibration curve.
Experimental: .
Details of the procedure are on pg 8-11 in the Pharmaceutical section of the 3rd year laboratory manual.
Instrumentation Used: .
Model Of HPLC used: Varian HPLC 9050.
Model Of Rotary Evapourator: buchi motivator b-200.
Chemicals Used: .
Reagent grade Caffeine 99%, .
Reagent grade Magnesium Oxide .
HPLC grade Methanol.
Tea leaves.
Dichloromethane .
Results:.
Weight Of Crude Caffeine Obtained: 0.0672g .
Caffeine makes up 2-5% of tea leaves.
Theoretical yield for caffeine should be between 2-5% of original weight of tea .
2% of 10.0017g ïƒ 0.200034g.
5% of 10.0017g ïƒ 0.500085g.
Theoretical yield (average) ïƒ 0.3500595g .