A practical guide to Karl Fischer titration for water content in pharma intermediates

Volumetric or coulometric pick by water content

The decision is straightforward and the wrong call wastes weeks. Coulometric KF covers roughly 1 ppm to 5% water and is the right choice for dry intermediates, APIs, and most solid-state pharma samples. Volumetric KF covers ~100 ppm to 100% water and is the right choice for solvents, syrups, and wet excipients. Outside those ranges you'll fight noise (coulometric) or precision (volumetric).

Sample preparation is most of the method

Solid samples with very low water content drift quickly once exposed to the room. Weigh into a septum vial inside a glove bag, inject through the septum, and document the elapsed time from weighing to injection in your SOP. For sticky or insoluble samples, oven evaporator coupling beats forcing dissolution in a single solvent.

Drift troubleshooting in three minutes

If the baseline drift won't stabilize: check the molecular sieves on the dry-air inlet, confirm the desiccant in the titration cell isn't spent, then look at the septum for damage. Eighty percent of drift complaints resolve at that level. Replace the reagent only after exhausting those.

What to put in your SOP

Drift acceptance criterion. Recovery on a water standard at the start of every shift. The clock on sample handling. A second-line reviewer signature on the weighing record. Methods that document these survive audits without follow-up findings.