PRECISE DETERMINATION OF LOW-LEVEL SUCROSE AMORPHISM BY MICROCALORIMETRY

The DSC curve of freeze-dried amorphous sucrose shows the glass transition, the crystallization and the melting (just before decomposition) of the sample. Sucrose crystallization occurs below 100-degrees-C: this phenomenon can therefore be observed with the microcalorimeter Setaram Micro-DSC used in the scanning mode. Mixtures of amorphous and crystalline sucrose in known proportions were used to calibrate the instrument. Low level amorphism (down to about 0.5%) could be detected and quantitatively evaluated on the basis of the crystallization enthalpies determined. The calibration curve obtained can be applied to determine the degree of amorphism in milled sucrose. A simple gravimetric method, based on the desorption of water induced by recrystallization of the amorphous layer can be used to obtain similar data more rapidly. This simple method is particularly useful for controlling the amorphism on line during a process, and is also briefly described.