Water-solid interactions. I: A technique for studying moisture sorption/desorption

Abstract Moisture sorption and desorption have been characterized for active (naproxen and paracetamol) and inactive pharmaceutical solids by using a climatic test chamber. The relative humidity (RH) of the climatic test chamber was varied in the range from 15 to 90%. Equilibrium moisture content was achieved within a period of 2 h for slightly hygroscopic and moderately hygroscopic substances. For very hygroscopic substances equilibrium was reached within 2 h at low RH ( 60%). Moisture sorption isotherms were characterized by using the climatic test chamber and were found to be identical with moisture sorption isotherms characterized by desiccators.