Method of Kinetic Analysis of Photodegradation : Nifedipine in Solutions

概要

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A rate equation for photodegradation was derived from Lambert-Beer's law and Grotthus-Draper's law : -dc/dt=k_1(1-exp(-(k_2c+k_3(c_0-c))))k_2c/(k_2c+k_3(c_0-c))where c is the concentration of reactant, c_0 is the initial concentration of reactant, t is time, k_1 is the rate constant, and k_2 and k_3 are the absorption coefficient of reactant and its photodegradation product, respectively.In a case where the photodegradation products have no photoabsorption, k_3 assumes the value of zero in the above general equation. In a case where the photodegradation products have the same spectrum and molar absorptivity as that of the reactant, k_3 assumes the value of k_2,and hence the photodegradation is not a first-order reaction; however, the equation itself gives the pseudo-first-order reaction rate equation. In a case where the concentration of reactant is high enough, the equation approaches a zero-order reaction rate equation.The photodegradation rate of nifedipine in solutions under a germicidal lamp, near an ultraviolet fluorescent lamp and a fluorescent lamp was analyzed using the above equation. The photodegradatino rate was directly proportional to the amount of light absorbed, and fitted well with the equation. The above theoretical equation was substantiated by the photodegradation of nifedipine, and hence is expected to apply to other photosensitive drugs.
社団法人日本薬学会の論文
1990-06-25