Abstract
The kinetics of the color change (ΔE) of sugar-coated tablets containing ascorbic acid in the core was studied by means of a differentiation procedure. The time course of ΔE for the cores under accelerated deterioration conditions was fitted to a curve, and the curve was differentiated with respect to time. The apparent rate constant for the color change was estimated from the differential coefficient on the assumption of an appropriate reaction order. The other kinetic parameters were obtained on the basis of the formulae described by Carstensen et al. The values of ΔE and moisture content for the tablets were examined in moisture-semipermeable packages kept in a storehouse for two years, and compared with the values predicted by an iterative calculation procedure using a mathe-matical model based on the moisture permeabilities and the kinetic parameters obtained here. The predicted values of ΔE in this study coincided well with the observed data, and it was found that there was a reasonable agreement between the shelf lives predicted in this study and those predicted in the previous paper. Thus, it might be concluded that the differential analysis procedure was useful for kinetic studies of the deterioration of solid dosage forms under the influence of the moisture content and ambient temperature.
