Introduction To USP <922>: General Chapter For Water Activity Measurement

By Michael Lally, Application and Validation Specialist at Lighthouse Instruments

The newly drafted USP <922> General Chapter describes the specific methods that pharmaceutical companies will use to calibrate, qualify, and use water activity instruments in their testing protocols. It is water activity measurements, not total water content, that correlate to critical product quality attributes. The latest updated version of the proposed chapter is available online via the US Pharmacopeia Forum (PF). The comment period for the proposed USP<922> General Chapter closed on 31-Mar-2020 and the official final chapter is targeted to be published in USP-NF 2021 at the beginning of 2021.

USP <922> includes a description of Tunable Diode Laser Absorption Spectroscopy (TDLAS) measurements and states that it is the only method to reliably and accurately measure water activity when the sample contains other volatile compounds. The Lighthouse FMS-Water Activity Analyzer uses TDLAS to non-destructively and directly measure the water activity non-invasively of samples in a sealed glass vial.