Karl Fischer water content

A titration method that measures the water remaining in a lyophilised powder — one of the reasons gross powder mass overstates the peptide a vial actually contains.

Karl Fischer titration is the standard analytical method for measuring water content in a solid or liquid sample. It relies on a chemical reaction that consumes water stoichiometrically, so the amount of reagent used translates directly into the amount of water present. For lyophilised peptides it answers a specific question: how much of the powder's mass is residual moisture rather than compound.

Freeze-drying removes most water but never all of it. A few percent of residual moisture is typical, bound tightly enough to survive lyophilisation, and it varies between batches and with storage. That water contributes to the gross weight of the powder while contributing nothing to the peptide content, which is one of the two standing reasons — the counterion being the other — why label mass and peptide mass differ.

Water content appears on peptide certificates less often than purity and identity, usually when a fuller characterisation was commissioned. Where it is reported, it allows net peptide content to be reconciled with the gross mass; where it is not, the moisture fraction remains an unmeasured part of the difference.

For research purposes only. Not for human consumption, diagnosis, treatment, or prevention of any condition. Nothing on this page is medical advice.