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Lab Notes: Extraction of Caffeine From Tea by Soxhlet Technique


             Experimental yield ïƒ 0.0672g.
             The experimental % yield = (experimental yield/theoretical yield) x 100.
             % yeild = (0.0672g/0.3500595g) x 100 = 19.20% ïƒ 19% .
             Optimumisation of Mobile Phase .
             Mixture(HPLC Methanol/water ratio) Observation:.
             70Methanol:30Waterïƒ Single peak .
             50Methanol:50Water ïƒ Single peak .
             30Methanol:70Water ïƒ Two distinct separate peaks .
             Calibration Curve.
             Concentration (mg/L) Theophylline peak area Caffeine peak area.
             2 7.68 1.26.
             5 7.68 2.44.
             10 7.68 2.84.
             15 7.68 4.23.
             20 6.72 4.24.
             Table 1 Table of results from chromatograms .
             Figure 1 Calibration curve of the concentration of caffeine (mg/L) vs. peak ratio.
             Purity of crude caffeine.
             Using the Y equation calculated above the concentration of caffeine can be calculated.
             Y = 0.025x + 0.1457.
             Where y is the value of the peak ratio and x is concentration in mg/L.
             35742 = 0.025x + 0.1457.
             x = (0.35742 - 0.1457)/0.025 ïƒ 8.47 mg/L.
             This is multiplied by 100 due to a dilution factor of 100 ïƒ 846.89 mg/L.
             The is then multiplied by 0.025 as the sol was made in a 25ml flask ïƒ 21.17mg/L.
             Discussion:.
             As the natural caffeine content of tea leaves was noted to be between 2-5% a range of the typical caffeine content could be found. From this range an average was taken. The average weight was then taken to be the theoretical yield. The experimental % yield of the sample was then noted to be 19%. This was a low yield this could be due to the conditions were not optimum for caffeine extraction. The loss of yield may be due to a number of factor. The ethanol, may not have been the best solvent which could have been used as other solvents may have shown a greater affinity to extracting the caffeine, also the run time could have been increased to optimise caffeine extraction. It was also noticed that when treating the solution with dichloromethane bubbling of the aqueous layer occurred. This could have caused the aqueous layer to remain in the organic layer. This would have affected the purity of the sample in the end and making the separation step void some of the caffeine was lost.


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