Calculation of the vapor pressure-temperature relationship using thermogravimetry for the drug allopurinol

Allopurinol sublimates when subjected to thermogravimetry in a nitrogen atm osphere. The process is zero order and plots of in k venus reciprocal tempe rature (K) give a value of 132.64 kJ mol(-1) for the activation energy. On the basis that equilibrium is achieved at all temperatures the data is used to establish a plot of the vapor pressure curve versus temperature from wh ich a Clausius-Clapeyron relationship can be used to establish the DeltaH f or sublimation. The method requires that the equipment is calibrated and da ta for p-aminobenzoic acid is used for this purpose. (C) 2001 Elsevier Scie nce B.V. All rights reserved.