spectrocopic method: characterization of caffeine and determination of caffeine in tea...
TRANSCRIPT
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SPECTROCOPIC
METHOD:
Characterization of caffeine
and determination of
caffeine in tea leaves using
UV-Vis spectrometer.
BY: SARAH ELEENA
JULIANA SHAIBUN
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PROBLEM STATEMENT
To determine the characterization of pure
caffeine
To determine caffeine content in twelve
commercial tea leaves using UV-Visible
spectrometer
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SAMPLING TECHNIQUE
Nature of population
- A set of twelve commercial tea samples
made up of five Ethiopian black teas
(Addis, Black lion, Cinamon, Tosign and
Ginger). These samples were from tea bags
except Black lion. Cinamon, Tosign and
Ginger tea leaves are blended teas with
cinamon, tosign and ginger respectively.
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Sample and sampling techniques.
• Tea leaves are heterogeneous solid
sample.
• Homogenization of solid sample by
grinding process of the gross sample.
• Cone and quarter method can be used to
reduce gross sample.
• Next, the sample is dissolved with distilled
water, then extract with different solvents
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SAMPLE PREPARATION
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(A) STANDARD SOLUTION PREPARATION
0.46 mg
caffein
+ 25 ml
dichloromet
hane
1.40 mg
caffein + 50
ml water
0.85 mg
caffein +
50 ml
chlorofoam
0.80 mg caffeine + 40
ml ethane acetate
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Measure the absorbance for each dilution
using UV- Vis spectrometer.
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(B) TEA SAMPLE PREPARATION (30 C)
50 mgTea leaves + 30ml distilled water
Stir 30 min then filter
Add 40ml dichloromethane
Stir
(10 min)
Separate layer using separating
Funnel
Pour dissolution in 1cm cuvette
Measure absorbance using
UV-Vis spectrometer
Extract dissolution & repeat the procedures
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Cool
at
21 ᵒC
Forms 2
layers
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(C) TEA SAMPLE PREPARATION (94 C)
(Using ethiopian origin (addis,black lion, cinnamon and green tea)
50 mgTea leaves + 30ml distilled water
Stir 3 min then filter
Add 40ml dichloromethane
Stir
(5 min)
Separate layer using separating
funnel
Pour dissolution in 1cm cuvette
Measure absorbance using
UV-Vis spectrometer
Extract dissolution & repeat the procedures
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Forms 2
layers
Cool
at
21 ᵒC
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PRECAUTION STEPS
Make sure the cuvette has no air bubbles
The cuvettes are cleaned and oriented
consistently in the light beam
The compounds to be examine is
completely dissolved
The spectrometer is in a proper state of
calibration and is well maintained at all
times
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INTERFERENCES
Caffeine content in tea leaves cannot be
determine directly using UV visible
spectrometer due to the matrix effect of UV
absorbing substance.
Removal of Interferences
Therefore, the sample need to be dissolved
in water and then extract using
dichloromethane to overcome the problem.
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CALIBRATION AND STATISTICS
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Figure 1 : Absorption spectrum of tea leaves in water
Caffeine spectra interface
with other compounds in
tea leaves.
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Figure 2 : Absorption spectra of pure caffeine and caffeine extracted from tea leaves
The absorption Spectra of pure caffeine and Caffeine Extracted by dichloromethane Exactly overlaps.
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Figure 3 : Overlapped spectra of caffeine extracted from Ethiopian green tea and cinamon tea.
Uv-vis absorbance range
of caffeine is from 243 nm to
302 nm
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Caffeine is better extracted at the
higher temperature
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Real Sample
A set of twelve commercial tea samples
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CONCLUSION
Optical transition properties of pure
caffeine and caffeine content of real tea
leaves at two different temperature were
analyzed and the result agrees with the
literature values of either analytical
methods.
• Caffeine is better extracted at the boiling
temperature (94 ᵒC) than that 30 ᵒC and
more extraction time.
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…THE END…
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