2.4.3. Dynamic Vapour Sorption (DVS)

The water vapour sorption of the substances (sieve fraction 32–150 µm) was determined using a DVS Resolution (Surface Measurement Systems Ltd., London, UK). The relative humidity was increased and decreased stepwise from 0% to 90% to 0% in isothermal conditions (25 °C). This program was conducted twice. Each step was held until mass equilibrium was reached. Hygroscopicity can be assessed by using the criteria from Ph. Eur. 10.0/5.11.00.00, which rate the gain in mass at 80% relative humidity and 25 °C. A mass gain of 0.2–2% is classified as slightly hygroscopic, a mass gain of 2–15% is classified as hygroscopic, and a mass gain of 15% and higher is classified as very hygroscopic.