Determination of the glass properties of D-mannitol using sorbitol as an impurity

Due to its strong tendency to crystallize, the glass properties of mannitol cannot be measured directly. However, because mannitol can exist in a fully or partially amorphous state in drug formulations, it is important to determine the glass properties of mannitol. We obtained the glass properties of mannitol by introducing a small amount of sorbitol, an isomer of mannitol, to delay the onset of crystallization. Extrapolation to zero sorbitol concentration yielded the following properties for the mannitol glass: T-g onset = 10.7 degrees C, T-g midpoint= 12.6 degrees C, T-g end = 18.4 degrees C and Delta C-p = 1.27 J/g/K. In addition, we estimated the following parameters of the mannitol glass from the width of glass transition using the results of Moynihan (J. Am. Ceram. Sec. 1993, 76, 1081) and Angell (J. Phys. Chem. 1994, 98, 13780). Delta H* (at T-g onset) = 103 kcal/mol, D = 11, and T-0 = 222 K. The value of T-0 is consistent with the Kauzmann temperature T-K (236 K) obtained calorimetrically. The properties of the mannitol glass may be useful for predicting the behavior of amorphous mixtures containing mannitol.