Quality
Purity vs Potency: Two Different Numbers
A 99 percent pure peptide can still deliver far less active than the label claims. The two figures answer different questions.
Key takeaways
- Purity is a proportion; potency is an amount.
- Peptide content is reduced by water, salts and counter-ions.
- Only potency connects to your actual dose.
Two questions, two answers
Purity asks: of the peptide-related material present, what fraction is the target sequence? It is typically measured by HPLC and reported as area percent.
Potency, or content, asks: how many milligrams of the target are in this vial or capsule? That is what determines your dose, and it requires quantitative assay against a reference standard.
A sample can be 99 percent pure and still contain far less peptide by mass than the label implies. The two numbers are not substitutes.
Where the missing mass goes
Lyophilised peptide is not pure peptide by weight. Typical composition includes bound and residual water, counter-ions such as acetate or TFA, and residual salts from purification.
Peptide content by weight — measured by amino acid analysis or quantitative nitrogen determination — commonly lands in the seventy to ninety percent range for material that is 98 to 99 percent pure by HPLC. Both numbers are honest. They measure different things.
Why area percent has limits
HPLC with UV detection at 214 nm responds to the peptide bond, so the response is broadly proportional to chain length. A deletion sequence one residue short produces slightly less signal than the full-length chain of the same mass, which subtly flatters the purity figure.
More importantly, area percent only counts what the detector sees. Inorganic salts, most residual solvents and water contribute nothing to the UV trace and are therefore absent from the purity number entirely.
What this means for comparison
Two products both claiming 1,000 mcg can differ materially in delivered active — through salt form, through peptide content basis, and through whether the label claim refers to the salt or the free peptide.
This is not usually deception. It is more often two manufacturers reporting on different bases without saying which. The fix is disclosure, and asking.
The specific question to ask
Is the label claim stated as peptide content, or as weight of the salt? Is potency verified by assay on the finished product, or inferred from the raw material certificate?
A manufacturer with a real quality system answers both without difficulty.
This article is educational and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.