SPECTROCOPIC

METHOD:

Characterization of caffeine

and determination of

caffeine in tea leaves using

UV-Vis spectrometer.

BY: SARAH ELEENA

JULIANA SHAIBUN

1

PROBLEM STATEMENT

To determine the characterization of pure

caffeine

To determine caffeine content in twelve

commercial tea leaves using UV-Visible

spectrometer

2

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.

3

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

4

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

Measure the absorbance for each dilution

using UV- Vis spectrometer.

6

(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

(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

8

Forms 2

layers

Cool

at

21 ᵒC

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

9

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.

10

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

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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