Early in the Research and Development of our Moisture Profiling™ technique we saw that the amount of sample being tested sometimes did, and sometimes did not, influence the equilibrium point. Precise control of sample mass was not a parameter traditionally used in Water Activity (Aw) measurements. Without historical data to rely upon we carried out our own detailed investigations into varying the mass of the test material. A simple way of representing our findings is to look at the moisture profiles and the Water Vapour Equilibrium Point (WVEP) of multiples of tablets as shown in the graph.
As you can see in the graph adding more material reduces the WVEP. Adding more tablets (Mass) results in the lowest WVEP achievable for the test sample. The lowest WVEP value for the material is a measure of the equilibrium %RH of the bulk material. In other words, within a pharmaceutical bottle containing for example 28 tablets, or inside a bulk storage container, the %RH of the air surrounding your product will be its lowest WVEP as measured by Relequa® Moisture Profiling™.