A THERMOGRAVIMETRIC STUDY OF ASCORBIC-ACID ANP ITS EXCIPIENTS IN PHARMACEUTICAL FORMULATIONS

The thermal decomposition of ascorbic acid and its excipients in table t formulations was studied under an atmosphere of nitrogen using a the rmogravimetric balance. To maximize the tendency of an interaction, bi nary mixtures (1:1 by weight) of drug and excipient and between excipi ents were utilized. Two new methods were employed to assess the change in reactivities, and the thermal behavior of the materials under inve stigation. In the first method, named the alpha(s)-alpha(r) method, th e solid state reactivity of the sample was compared to that of a refer ence. The term alpha 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 W-p and W-t refer to the percentage of residual solid mate rial obtained experimentally (W-p) and theoretically (W-t). The ratio W-p/W-t is reported at various values of temperature.