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Water activity, or equilibrium relative humidity (ERH%), is widely used as a quality control measure in pharmaceuticals to maintain the stability of the composition and effectiveness of the active ingredients (API).

Normally, very low water activity control measures for pharmaceuticals are needed which mean that measuring instruments require calibration at ultra-low humidity levels with reliable traceable standards. Often there are also high-solvent contents in samples which necessitate specific filters for the sensor cell to protect it from contamination and consequent calibration drift. These special REDOX filters act as a barrier to allow only water molecules to pass through to the sensor cell and give reliable readings.


Challenges in measuring water activity

Often there are high concentrations of solvents in samples, eg glycerol as a humectant, which can lead to slow aw readings, false results or damage and sensor drift for the water activity meter. It is therefore important to use a sensor protective alcohol and chemical filter in the aw meter to block these effects

Toothpaste aw