Pharmeuropa: Revision Proposed for Chapter 2.5.32 on Coulometric Karl Fischer Water Determination

A draft revision of European Pharmacopoeia (Ph. Eur.) general chapter 2.5.32. Water: micro determination has been published for public consultation in Pharmeuropa 38.4.

The proposed text adds dedicated instructions on three operating parameters for the evaporation (oven) technique:

• temperature,
• carrier gas flow rate,
• heating time.

These parameters should ensure that water is fully transferred to the titration cell without causing sample decomposition or introducing interfering substances.

The briefing note states that "clarifications on the operating principle and procedure, in particular the necessity to control the background drift, as well as the applicability of reference substances for either direct introduction or evaporation techniques, have been added."

Background drift should be stable and low, typically below 20 µg/min. Coulometric titration is intended for determining small quantities of water from 10 µg, while a working range of 100 µg to 10 mg is recommended for reproducibility.

The draft also specifies that when an individual monograph gives a temperature, the evaporation technique is to be used. If no temperature is specified, direct sample introduction is to be used.

The draft also renames the “Verification of Accuracy” section as “System Suitability” and sets recovery criteria for both direct sample introduction and evaporation.

The draft text is available on the Pharmeuropa website (login required). The public consultation deadline is 31 December 2026. Comments can be submitted via the Pharmeuropa platform.