Characterization of Amorphous Solids with Weak Glass Transitions Using High Ramp Rate Differential Scanning Calorimetry

Measurement of the glass transition temperature (Tg) of proteins and other high molecular weight polymers in the amorphous state is often difficult, since the transition is extremely weak, that is, the ΔCp at the glass transition temperature is small. For example, little is known about the solid-state properties of hydroxyethyl starch (HES), which is beginning to become more commonly evaluated as a bulking agent in pharmaceutical products. For weak thermal events, such as the change in heat capacity at the Tg of a pure protein or large synthetic polymer, increased heating rate should produce greater sensitivity in terms of heat flow. Recent innovations in rapid scanning technology for differential scanning calorimetry (DSC) allow measurements on materials where the thermal events are difficult to detect by conventional DSC. In the current study, measurements of the Tg of proteins in the solid state, amorphous pharmaceutical excipients which have small ΔCp at the glass transition temperature, and bacterial spores, have all been made using high ramp rate DSC, providing information on materials that was inaccessible using conventional DSC methods. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:1013-1024, 2008