A thermogravimetric study of ascorbic acid and its excipients in pharmaceutical formulations

The thermal decomposition of ascorbic acid and its excipients in tablet formulations was studied under an atmosphere of nitrogen using a thermogravimetric balance. To maximize the tendency of an interaction, binary mixtures (1:1 by weight) of drug and excipient and between excipients were utilized. Two new methods were employed to assess the change in reactivities, and the thermal behavior of the materials under investigation. In the first method, named the αs−αr method, the solid state reactivity of the sample was compared to that of a reference. The term α refers to the extent of the reaction. The second method is called the W p W t method. In this method, the effect of the excipients on the decomposition pattern of ascorbic acid can be shown. The terms Wp and Wt refer to the percentage of residual solid material obtained experimentally (Wp) and theoretically (Wt). The ratio W p W t is reported at various values of temperature.