Abstract
A new kinetical equation for a gas-solid reaction which is convenient for use in predicting the degradation of a pharmaceutical solid is derived, and a procedure of analyzing accelerated storage data is proposed. The procedure is applied to the air oxidation degradation of ascorbic acid in a mannitol conglomerate. The result of the analysis was consistent with that obtained by Lacey's procedure. With the proposed procedure, operational difficulties met in Lacey's procedure were overcome. The temperature dependence of diffusivity is found to be 56 kcal/mole, with an activation energy for the chemical reaction of 26 kcal/mole. The rate constant for the chemical reaction at 25° is estimated to be 3.3×10-6 hr-1, a value which is consistent with the results of Tardif, which were obtained from a different point of view.
