How it works
The method relies on a reaction that consumes water in a defined stoichiometry. Because the reaction is specific to water, the measurement reports water content rather than total volatiles — a distinction that matters for a hygroscopic powder that may also hold residual solvent.
Two variants exist — volumetric and coulometric — differing in how the water-consuming reagent is delivered and quantified; coulometric titration suits the low water levels typical of a well-dried lyophilate.
Karl Fischer measures a property of the physical material, not of the molecule. Two lots of the same peptide with identical formula and mass can carry different residual water, which is why it is a lot-level rather than a molecule-level measurement.
Why it matters
Residual water bears on stability and on how a mass-based measurement is interpreted: water is mass, so a damp lyophilate weighs more than the peptide it contains, and knowing the water content lets that be accounted for.
Because water uptake is a handling and storage concern, a residual-water figure is a snapshot of a lot at test time, not a permanent property — another reason it belongs to the lot, not the molecule.
It measures moisture, and nothing more. A water figure says nothing about identity or purity, which are established separately by ESI-MS and RP-HPLC.
At Lineará
Lineará compounds are supplied as lyophilized powders, and residual-water control is part of why a peptide ships dry rather than in solution.
Water content is a physical-lot property, distinct from the identity (CAS, formula, mass) and purity a certificate reports; where a lot’s water assay is supplied, it belongs with the lot record, not the molecule.