Monitoring hydration state conversion by TG-DTA

Characterization of the solid-state form (hydrate or polymorph) of a pharmaceutical active is a key scientific and regulatory requirement during development of and prior to seeking approval for marketing of the drug product. A variety of analytical methods are available to perform this task. By nature of the fundamental information it provides, TG-DTA offers advantages over other methods in regards to monitoring and quantitation of hydration state changes. In a single experiment with only a few milligrams of sample, TG-DTA perceives minor changes in phase, quantitates total water content and percent conversion, and illustrates hydrate type. All of this is accomplished without the necessity of generating time-consuming standard curves representing the differing ratios of hydrated to anhydrous forms. This study describes the use of TG-DTA to monitor and quantitate humidity induced solid–solid phase conversion of nitrofurantoin and risedronate. Percent conversion was qualitatively observed by both TG and DTA signals and quantitated by the TG.