How to Verify a Peptide Supplier: Reading a Certificate of Analysis
A certificate of analysis is the single most important document a peptide supplier can give you, and the easiest to fake badly. Here's how to read one properly, what a legitimate certificate always includes, and the tells that separate real testing from a PDF someone made in an afternoon.
Who ran the test?
The first thing to check is the laboratory. A credible COA comes from an independent, ISO 17025-accredited third-party lab — not from the supplier's own bench and not from a manufacturer with a financial interest in the result. Marinexis releases every lot only after third-party testing, and the certificate names the lab.
The six numbers that matter
- HPLC purity. The percentage of the material that is the intended peptide versus related impurities. Marinexis's release specification is 99% or higher; a lot that tests below is rejected and never enters inventory.
- Mass-spec identity. Confirms the molecular weight matches the intended sequence. Purity without identity is meaningless — a 99% pure wrong molecule is still the wrong molecule.
- Net peptide content. How much of the vial's mass is actually peptide after subtracting water and counter-ions. A "10 mg" vial with 70% net content contains 7 mg of peptide.
- Water content. Excess moisture accelerates degradation of lyophilized product.
- TFA (trifluoroacetic acid). A residual from synthesis and purification; reputable suppliers quantify it.
- Endotoxin. Bacterial endotoxin levels, critical for anything intended for sterile use. Its absence from a COA is a serious red flag.
Red flags
- No lot number, or a lot number that doesn't match the vial label.
- Purity reported without a chromatogram or method summary.
- A single generic certificate reused across many products.
- A supplier that will show you "a COA" but not one for the lot you're actually buying.
- Refusal to ship samples for your own independent test.
The verification that beats any document
Send samples to a lab you choose. Marinexis ships pre-order samples of any SKU for independent testing, invoiced at cost and pulled from the same lot that would fulfil your PO. A supplier who won't do that is telling you something.
Related reading: lot traceability and recalls.
Want to see a real COA?
Recent third-party certificates for any catalog compound are available on request.
Request a COAProducts supplied through the Marinexis wholesale channel are sold strictly for laboratory research use and are not for human consumption or clinical, diagnostic, or therapeutic use. Clinical products are supplied only to licensed practices and dispensed through licensed pharmacies pursuant to valid prescriptions. Nothing in this article is medical, legal, or financial advice.