ASSESSMENT OF THE DEGREE OF DISORDER IN CRYSTALLINE SOLIDS BY ISOTHERMAL MICROCALORIMETRY

The use of isothermal heat-conduction microcalorimetry for assessment of degree of the disorder within crystalline material has been evaluated. Single entities, physical mixtures with varying contents of 100% amorphous lactose and 100% crystalline alpha-lactose monohydrate, and samples of spray dried lactose with varying degrees of disorder were analysed at 25 degrees C. The technique monitors the heat flow from the crystallisation of the amorphous content of the powder, when the powder is exposed to a humid environment. The heat calculated from the heat flow curve by integration revealed good linearity. The technique was able to detect at least 2% disorder in a crystalline sample. Comparisons with X-ray analysis and DSC showed good agreement above 10% disorder. At lower degrees of disorder only microcalorimetry was able to measure the disorder with high accuracy.