Karl Fischer Water Determination
Definition
The standard laboratory assay for water content in a dry solid, using an iodine reaction specific to water. On a lyophilised peptide it reports residual moisture, which is a stability predictor, and the result is reported as a mass fraction of water in the solid.
In more detail
The Karl Fischer method measures water content specifically, through a reaction that consumes water, rather than inferring it from mass lost on drying. For a lyophilised peptide that specificity matters, because loss on drying also drives off residual solvent and counts it as water.
The result is what allows a purity figure to be converted between an as-received and an anhydrous basis. Without it the two cannot be related, and a certificate quoting an anhydrous figure with no water determination behind it has made an assumption rather than a measurement.
What this means for research sourcing
Purity and identity verification are central to research reproducibility. Every Volta compound ships with >99% HPLC-verified purity and a certificate of analysis.
Related Terms in Quality
Purity
The proportion of a sample that is the intended peptide rather than related impurities, measured chromatographically and quoted as a percentage. It says nothing about identity, sterility or endotoxin content, each of which is a separate test. Volta releases every batch against a >99% HPLC specification.
Endotoxin
Lipopolysaccharide from the outer membrane of Gram-negative bacteria. It survives ordinary sterilisation and is not removed by filtration alone, and it provokes a febrile inflammatory response, which is why it is assayed separately from sterility.
LAL Test (Limulus Amebocyte Lysate)
The endotoxin assay, which uses a clotting cascade from horseshoe crab blood that endotoxin triggers. A result on a certificate is a quantity against a limit, not a yes or no.
Sterility Testing
Incubation of a sample in growth media to confirm no viable microorganism is present. Sterility is a property of a validated process and its container and is independent of chemical purity: a very pure material can be non-sterile and often is.
Sterility
The absence of viable microorganisms in a preparation. It is conferred by a process and preserved by a closure, so it is lost the moment either is compromised and nothing about the appearance of a vial reports that.
Assay
Any procedure that measures whether something is present, how much of it there is, or how active it is. Analytical assays report composition; functional assays report activity, and a material can pass one and fail the other.
Quality Control (QC)
The testing a batch passes through before release, typically identity by mass spectrometry, purity by HPLC, content and, where relevant, water, sterility and endotoxin. QC is the set of tests; the certificate is the report of their results.
Degradation Product
A compound formed as a peptide breaks down, through oxidation, deamidation, hydrolysis or aggregation. Certificates report these as impurity peaks, and their pattern says more about how a batch was handled than the headline purity figure does.
