1991 Volume 39 Issue 4 Pages 1027-1031
Effect of mixing with a controlled pore glass (CPG) on the stability of aspirin was studied under conditions of various relative humidities (RH), pore diameters of CPG and concentrations of aspirin. The crystallinity changes of aspirin in the mixtures with CPG170 or CPG3000 were also studied using the powder X-ray diffraction method and microscopy. The amorphous aspirin in the CPG mixtures showed an extremely fast decomposition rate, and a high rate was obtained when the pore diameter of the CPGs were less than 300 Å. In the mixtures of small pore diameter CPG, the decomposition rate constants were greater at a lower RH. These results can be explained in terms of the catalytic effect of free silanol groups on the surface of the CPG.