Article: Introduction to USP-922 General Chapter for Water Activity Measurement

The (drafted) USP <922> General Chapter describes methods for water activity determination in testing protocols. It is water activity, not total water content, that best correlates to critical product quality attributes. USP <922> includes a description of tunable diode laser absorption spectroscopy and states that it is the only method to reliably and accurately measure water activity when the sample contains other volatile compounds. This article summarizes the importance of water activity and how laser-based headspace analysis can be used for water activity determination.