6 Aug 2014 | 13:39
By Dr Jürgen Dienstmaier
The Dynamic Vapour Sorption Instrument (or DVS for short) was developed as a response to the pharmaceutical and industrial researcher’s need for fast and effective analytical methods to determine a material’s moisture content and related sorption isotherms.
Before the invention of the DVS, water sorption isotherms were obtained from a process known as the “Jar Method” or desiccator method. It was a slow and tedious process that took weeks, if not months, to achieve results. In short, the older method created a fixed water activity/relative humidity within a sealed container or jar by use of a salt slurry beneath a sample platform while maintaining the container at constant temperature. The sample would then be taken out of the container on a regular basis, weighed and returned to the container. When the change in mass was almost invariable between successive weighing, then the sample had achieved equilibrium (isotherm point) at that relative humidity (RH). If a complete isotherm, from 0% up to ~95% RH was required, many containers were needed. Further complicating the complete isotherm method, only experimental relative humidity values of known salt slurries were available thereby limiting the amount of equilibrium points used to construct the isotherm. This lengthy work was extended even further if experiments at several different temperatures were required. Considering the extreme work involved in preparation and measurement along with the chance to lose or contaminate samples during the weighing transfer process, it is understandable that a faster, simpler and more cost-effective method was urgently required.