Use of sub-ambient DSC to complement conventional DSC and TG

Abstract

Several drug substances or excipients are hygroscopic. The uptake or loss of water of such substances is generally difficult to control during processing or storage of drug products. DSC instruments with sub-ambient temperature equipment allow the determination of the amount of freezable water by measuring the corresponding melting enthalpy. The determination of freezable water adds valuable information complementary to TG analysis for understanding the processing and storage of raw materials and drug products. Several substances were tested as is, without treatment, after storage at 92% r.h. and after equilibration with water. The results of these experiments showed that it was possible to demonstrate defined hydrate formation, to determine the upper level of binding of water in amorphous substances and to confirm reversible hydrate formations demonstrated by temperature resolved X-ray diffraction.