Determination of caffeine concentrations of Ethiopian export standard coffee samples and the investigation of Optical and Quantum mechanical transition properties of caffeine molecule by UV/Vis- absorption spectroscopy

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Addis Ababa University


In this thesis, determination of caffeine concentration in aqueous solution of medium roasted export quality coffee bean samples performed by using UV/Vis absorption spectroscopy. Using UV/Vis absorption spectroscopy the molar decadic absorption coefficients and transitional dipole moment of pure caffeine in distilled water and DCM were obtained at 273 and 276 nm. The molar decadic absorption coefficients of caffeine in water and dichloromethane at these wavelengths were 1125.035 and 376.06m2mol-1, respectively. The calculated values for the transitional dipole moment of caffeine in distilled water and in DCM were 6.70 x 10-30and 11.63 x 10-30C m for the given concentration in wave number range of 2,800,000 to 4,100,000m-1 respectively. After characterizing caffeine in water and DCM, a simple, rapid, cost-effective, and environmentally friendly UV/Vis absorption spectroscopy method was developed that enables to quantify the concentration of caffeine in coffee beans. Caffeine extracted with dichloromethane (DCM) from aqueous solution of coffee in distilled water to get UV/Vis absorption spectrum. The inference matrix was eliminated by fitting Gaussian function to the spectrum band of the experiment. From absorption spectrum optical & quantum transition mechanical properties such as; integrated absorption coefficient, integrated absorption cross-section, oscillator strength, dipole moment, and Einstein B coefficient as well as number density of caffeine molecule were calculated in DCM and distilled water. Optical & quantum transition mechanical property shows us the intrinsic ability of molecules to absorb light and these were proportional to the intensity of transition. The concentration of caffeine in medium roasted Ethiopian export standard coffee samples expressed in percentage ranged from 1.34% to 2.51% by BLL and by IAT. These finding will help Ethiopian coffee storage & liquoring board, Ethiopian standard agency, and Farming & agricultural ministry of Ethiopia for specifying caffeine concentration in each coffee samples. The highest caffeine concentration in this work was found in Teppi & washed Sidama coffee samples and the lowest caffeine concentration was found in Limu coffee sample. The caffeine concentration for Ethiopian export standard roasted coffee in this work was in a good agreement with other researchers reported on roasted Arabica coffee samples by the same method Key words: - Export standard, optical transition, caffeine, concentration, absorbtion spectroscopy, Einstein B coefficient



Export Standard; Optical Transition; Caffeine, Concentration;Absorbtion Spectroscopy; Einstein B Coefficient