. The presence of amorphous materials can be wanted or unwanted, depending on the desired or undesired unique properties of the amorphous state. Even relatively low levels of amorphous material (<10%), may have a detrimental impact on the stability and manufacturability of the formulated drug product. Disordered materials are inherently metastable and provided with thermal or mechanical energy will tend to revert to a more thermodynamically stable, crystalline form. For these reasons, investigating the level of disorder or thermodynamic state of pharmaceutical materials is critical in their formulation, storage and processing.
This overview paper highlights how vapor sorption techniques can be used to study pharmaceutical solids ranging from the lowest-energy crystalline state, to higher energy polymorphs and solvates, to defect sites, to completely amorphous materials. Dynamic Vapor Sorption (DVS) and Inverse Gas Chromatography (iGC SEA) are well-established techniques used for the determination of surface and bulk properties of powders, fibers, and films. The aim of this paper is to focus on the applications of these techniques as they relate to thermodynamic stability in pharmaceutical materials.