Question

What precautions would have to be taken when measuring free water in a liquid? How would the measurement be made?

Answer 1

Water activity is a measure of water in a material that is available to react with or attach itself to another material. This unattached water is referred to as “Free" water, while the unavailable water is called “Bound”.

How is Water Activity Measured?

The typical system uses a sealed temperature controlled chamber. A sample is placed in the chamber and sealed. The free water is allowed to escape into the air in the chamber. it remains there until all the free water has left the sample. (A condition of equilibrium)

At equilibrium the relative humidity of the air in the chamber is measured. The relation of this reading to pure water is the water activity measurement expressed as the term aw. The range of water activity is from zero (no free water) to 1.0 (pure water)

Precautions:

1. chamber should be sealed

2. Temperature should not change