Recrystallization, Phase Composition, and Local Structure of Amorphous Lactose from the Total Scattering Pair Distribution Function

Total scattering pair distribution function (TSPDF) analysis of synchrotron X-ray diffraction data has been used to study the structural characteristics of amorphous lactose and its subsequent recrystallization on aging. This shows that the recrystallization kinetics vary substantially between spray dried, lyophilized, and melt quenched samples aged at 40 °C/75% relative humidity (RH), although all samples consistently form the stable α monohydrate when crystallization does occur. Using TSPDF it was possible to quantify the amount of amorphous and crystalline phases present, as well as to extract other structural information such as crystallite size, as a function of time during aging from the different starting materials. We also were able to determine a correlation between a higher degree of local molecular ordering in the amorphous phase with decreased stability against recrystallization. This study shows the rich information that may be obtained from a TSPDF analysis of recrystallization from the amorphous state in organic systems.