Thermal aging phenomena in chitosan-related pharmaceutical systems

Results are presented of detection of thermal aging in the chitosan/ketoprofen acid (KTA) system, using low-frequency dielectric spectroscopy. Aging leads to substantial changes of the low frequency dielectric properties of the system. In order to identify the reasons for the detected aging, near infra-red (NIR) Raman spectra and distribution of molecular weights as well as direct measurements of water content were carried out. The additional measurements suggest that water desorption is mainly responsible for the detected aging phenomena. Formation of a charge transfer complex between the anionic carbonyl group of KTA and the cationic NH3/sup +/ group of chitosan, has also been detected.