Judging quality & evidence
How to read a peptide certificate of analysis
The short answer
A useful certificate of analysis names the peptide, the lot number, the testing laboratory and its methods, and shows the HPLC chromatogram rather than only a purity figure — plus mass-spectrometry identity data and the net peptide content. A certificate missing the lot number, the lab name, or the chromatogram cannot be verified by anyone. And purity is not content: a vial can be 99% pure and still be only 75% peptide by mass.
Key facts
- Purity
- Peptide vs. peptide-related impurities
- Net peptide content
- Peptide vs. everything — water, salts, counter-ions
- Identity
- Only mass spectrometry confirms it
- Sterility & endotoxin
- Invisible to purity testing. Separate assays.
What a certificate of analysis is for
A certificate of analysis describes one specific batch of material. It is not a statement about a vendor, a product line, or a brand. Its entire value rests on being traceable to the vial in your hand.
That is why a lot number matters more than the purity figure everyone quotes. If a vendor cannot tell you which batch your vial came from and show you the matching certificate, the document describes someone else’s vial.
Purity is not content — the field’s most expensive confusion
Purity compares the peptide against the by-products of its own synthesis: truncated chains, deletion sequences, oxidised variants. It is measured by HPLC, and expressed as the percentage of the detected material that is the target peptide.
Net peptide content compares the peptide against everything in the vial — water, counter-ions, salts, bulking agents. The HPLC detector cannot see mannitol or trifluoroacetate, so they never enter the purity calculation.
The consequence is concrete. A vial can be 99% pure by HPLC and 70–85% peptide by mass. If a 10 mg vial is 75% net content, you have 7.5 mg of peptide — and every dose you calculated from the label is 25% high. Ask for both numbers.
What purity cannot tell you
Purity says nothing about identity — 99% of something is still 99% of something. Only mass spectrometry, comparing observed mass to theoretical mass, confirms the vial contains the peptide you ordered. Purity also says nothing about sterility, heavy metals, or bacterial endotoxin, each of which needs its own assay.
Reading the document, line by line
Work through it in this order. Anything missing is a question for the vendor, and the questions themselves are diagnostic — a source that answers them directly is a different kind of operation from one that replies with marketing copy.
- Lot number — does it match the number printed on your vial?
- Laboratory name — is an independent lab named, or was this run in-house by the seller?
- Analysis date — is it recent, and does it belong to the batch being sold?
- The chromatogram itself — not just the percentage. A number with no trace cannot be checked by anybody.
- Mass spectrometry — observed mass against theoretical mass for the stated sequence.
- Net peptide content and salt form — how much of the vial’s mass is actually peptide.
- Endotoxin, sterility, heavy metals — for anything injected, these belong on the certificate.
How fabricated certificates give themselves away
Real analysis is untidy. Genuine chromatograms carry baseline noise and small satellite peaks, and purity drifts from batch to batch — honest figures tend to cluster somewhere around 98–99.2%. A catalogue in which every product is exactly 99.9%, with flawlessly symmetric peaks on a perfectly flat baseline, is describing a graphic rather than a measurement.
Independent laboratories publish their results in a public database keyed to an identifier printed on the certificate — typically a report or task number together with a case-sensitive verification key. Enter those credentials on the laboratory’s own portal. If they return no record, the certificate was fabricated. It takes two minutes and it settles the question.
Note also that matching a lot number is necessary but not sufficient. FDA seized counterfeit Ozempic bearing a genuine lot number; the counterfeits were distinguishable only by where the EXP/LOT text sat on the label.
Frequently asked questions
Does 99% purity mean a peptide is safe?
No. Purity measures the peptide against peptide-related impurities from synthesis. It says nothing about identity, sterility, heavy metals, or bacterial endotoxin — each requires a separate test. A perfectly pure, correctly identified peptide can still be non-sterile.
What is the difference between purity and net peptide content?
Purity compares the peptide to other peptide-like impurities. Net peptide content compares it to everything in the vial, including water, salts, counter-ions and bulking agents. A vial can be 99% pure and only 75% peptide by mass, because the HPLC detector never registers the rest.
How do I verify a peptide COA is real?
Take the report number and case-sensitive verification key printed on the certificate and enter them on the issuing laboratory’s own public portal. If the credentials return no record, the certificate is fabricated. Separately, confirm that the lot number on the certificate matches the lot printed on your vial.
Is an in-house COA worthless?
Not worthless, but not independent verification either. An in-house certificate is a self-report by the party with a commercial interest in the result. Only a certificate from a named, independent laboratory is third-party verification.
Sources
Every link below was checked and resolved before publication. Where a claim could not be traced to a primary document, we left it out.
Written by Pepperz Editorial and not medically reviewed — see our editorial standards. Educational reference only. Pepperz does not provide medical advice, diagnosis, treatment, prescribing guidance, or dosing recommendations.