Home › Learn › How to read a peptide CoA (2026)
How to read a peptide CoA.
The short answer
Read a peptide CoA in this order: verify it against the lab's system first; then check quantity against the label claim; then purity, remembering it is chromatographic purity (% of peak area), not absolute content; then the identity basis — retention-time co-elution is presumptive, only mass spectrometry confirms. A CoA without a verification path is just a PDF.
Before reading
Verify, then read — not the other way round
A CoA is a file, and files are editable. Every legitimate laboratory provides a way to check a report against its own records: a task ID and key, a QR code, or a public database entry. If the document in your hands cannot be verified, nothing else on it matters.
The four numbers
What each line means
- Quantity (mg/vial). The measured content versus what the label claims. Serious labs run duplicates and show both values; a single unreplicated number deserves less confidence. Deviations beyond roughly ±10% of label claim are commonly treated as failures in community datasets.
- Purity (%). Almost always chromatographic purity: the main peak’s share of total integrated area at a stated wavelength (usually 214 nm for peptides). It is not a statement that the vial is X% peptide by mass — water and counter-ions are invisible to it. 99% chromatographic purity with 15% water content is entirely possible and not a contradiction.
- Identity. “Retention time consistent with standard” means presumptive identity: strong evidence, not proof — different molecules can co-elute. Only a mass-spectral match confirms identity. An honest CoA states which basis it used.
- Method & version. The CoA should reference the method used. A lab that publishes its method lets you interrogate the result; one that does not is asking for faith.
The traps
Four ways a real CoA still misleads
- The wrong vial’s CoA. A certificate for batch A shipped with batch B. Batch numbers on the CoA must match the product in hand.
- Purity without quantity. 99% pure says nothing about whether there are 5 mg or 3 mg in the vial. Both numbers or it is half a report.
- “Tested” without a date. A 2024 CoA proves nothing about 2026 stock.
- Impressive-looking add-ons absent. Sterility, endotoxin and heavy metals are separate assays. If they are not on the report, they were not tested — and an honest report says “not tested” rather than staying silent.
FAQ
Common questions
What does 99% purity actually mean on a peptide CoA?
It means the main peak accounted for 99% of the integrated chromatogram area at the stated wavelength. It is a ratio between peptide-related peaks — not a claim that 99% of the vial's mass is peptide, since water, salts and counter-ions do not absorb the same way.
What is the difference between presumptive and confirmed identity?
Presumptive identity means the sample eluted at the same retention time as a reference standard under the same method — strong evidence, but co-elution of different molecules is possible. Confirmed identity requires mass spectrometry matching the molecular mass. A trustworthy CoA states which one it delivered.
Can a peptide CoA be faked?
The PDF can. That is why verification against the laboratory's own system — task ID, unique key, QR, or a public database entry — matters more than the document. A CoA that exists only as a file should be treated as unverified.
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