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Authors: Tesfaye, Wakgari
Keywords: Caffeine
Pseudo Zero-Order
Monoexponential fit
Date Added: 6-Sep-2007
Abstract: In this project optical properties of pure caffeine, i.e., time dependency of caffeine in coffee powder and solution kept under different conditions and temperatures were investigated. For the pure caffeine molar decadic absorption coefficient and transitional dipole moment were computed and found to be (1095 ± 37) m2 mol−1 and (11.3 ± 0.2)⋅10−30 C m. Respectively in all the systems and temperatures caffeine in coffee was investigated , a decrease in caffeine concentration as a function of time was observed. For the solution both in closed and open storage conditions the pseudo zero order kinetics was observed. The rate constant of decomposition = 2.41667x10dk−5 mol m−3 hr−1 for closed system and = 5.50417x10dk1−−5 mol m−3hr−1 for open system were determined. The linear regression coefficient values were above R = 0.99 in both cases. The half-life time of caffeine were 1177 hr and 517 hr for closed and open systems, respectively. In the contrary, for open powder system the kinetics obeyed the expected first order rate expression. For open powder coffee the monoexponential fits resulted in rate constant of decay at room temperature (23 °C) and in ambient atmosphere is computed to be k and half-life time of caffeine is 289 hr, which implies again chemical reaction during half-life was fastest for powder form storage than other conditions. Reaction rate was faster, as expected, for storage at 23 °C than 8 °C.
Description: A Thesis Presented to The School of Graduate Studies The Faculty of Science Addis Ababa University In partial Fulfillment of the Requirements for the Degree of Master of Science in Physics
URI: http://hdl.handle.net/123456789/97
Appears in:Thesis - Physics

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