Moisture Profiling™ and the WVEP

Moisture Profiling™ was created by Relequa from observing the way materials initially interact with moisture in the air. Using relative humidity (%RH) as a measurement of moisture in the air, we looked at moisture uptake in different types of materials, and particularly in pharmaceutical tablets. Our unique approach is a variation on Water Activity (Aw) measurement. The crucial difference in our test methodology is that we always set up the starting %RH at a point above the Equilibrium Relative Humidity of the material.

By applying this approach we can guarantee that the material will adsorb moisture and we see this in the moisture profile as decreasing %RH. As you can see in the figure below of various tablet products the %RH measurement generates a profile of moisture sorption that comes to an equilibrium point. To distinguish our Moisture Profiling™ technique from Aw measurement we call the end of the moisture profile the Water Vapour Equilibrium Point or WVEP.

Every tablet product we have tested over the past 10 years, involving hundreds of moisture profiles, has a WVEP of around 65% or less. The vast majority of WVEP values are less than 60%. Products with a low WVEP, of no more than about 35%, can take several hours to reach their WVEP. However, we have made no attempt to accelerate moisture uptake of low WVEP products. The natural moisture profile of a material contains valuable information about its moisture interaction behaviour that is influenced by its chemical and physical characteristics.