What Is a COA for Peptides?

A COA (Certificate of Analysis) is a document issued by an analytical laboratory that verifies the identity, purity, and quality of a specific peptide batch. It typically includes HPLC (High-Performance Liquid Chromatography) results showing purity percentage and mass spectrometry (MS) data confirming the peptide's molecular weight matches the target sequence.

What a COA Contains

HPLC purity: The most critical number. Shown as a percentage (e.g., 98.7%) representing the proportion of target peptide in the sample. Reputable suppliers deliver ≥98% purity. The COA includes the HPLC chromatogram — a graph showing peaks for the target peptide and any impurities.

Mass spectrometry: Confirms molecular identity. The observed molecular weight should match the theoretical weight of the target peptide sequence within ±1 Da (Dalton). This ensures you received the correct compound, not a different peptide at the same purity.

Additional data may include: batch/lot number, synthesis date, appearance (usually white lyophilized powder), solubility, net peptide content, sequence, and storage recommendations.

Why COAs Matter

Without a COA, you have no way to verify what you're working with. Research results built on unverified peptides are unreproducible at best and dangerous at worst. A 2019 study analyzing peptides from online suppliers found significant discrepancies between advertised and actual purity in products without third-party COAs (PMID: 30816438).

Testing is not one thing, though, and evidence comes at different distances from the vial in your hand. From strongest to weakest: (1) a per-lot COA commissioned by the seller and verifiable with the named laboratory — the strongest link, because the document is tied to one production lot and the lab will confirm it; (2) group-buy testing, where a panel from a shared batch is sent to a named third-party laboratory by one of the purchasers — real independent evidence about the same material, with a looser link to your particular vial; (3) a supplier-commissioned COA — the manufacturer's evidence about its own material; (4) nothing at all, or a certificate that cannot be verified with the laboratory that supposedly issued it. The useful question is not "does this vendor clear the bar" but "which rung is this document standing on, and can I check it?"

Red Flags

Be wary of: missing chromatograms (just a number without the graph), COAs that look identical across different peptides or batches, certificates that name no laboratory at all, and suppliers who will not produce the underlying report on request. A missing lot number is worth asking about, but it is not by itself proof of anything — group-buy and supplier-commissioned certificates often carry no lot you could match to your vial, and an honest vendor will tell you so. What is a genuine red flag is a vendor who lets you believe a certificate proves more than it does.

The sharpest test is verifiability. Some laboratories publish every result in a public database you can query with the numbers printed on the document; the rest have a phone number and will confirm whether they issued a report. A certificate you cannot check is worth less than a weaker-tier certificate you can — verifiability, not tier, is the real red flag.

Turning the Checklist on Ourselves

NorthPeptide is a distributor, not a laboratory. We do not run our own analysis, we are not the client on any certificate we hold, and we do not operate a per-batch or per-lot certificate programme. Published lab results, where they exist for a compound, are listed on our test results page along with the party that commissioned each one — either the manufacturer that makes the material, or another participant in a shared test. Those results cover eighteen compounds; most of the catalogue has no published result of any kind, and the page does not pretend otherwise.

On the ladder above, that puts us on rungs two and three — group-buy testing and supplier-commissioned certificates — not on rung one. We buy our material on our own account, not in shared group purchases; what is shared is the cost of the testing. Buyers of the same manufacturer's material pool funds to send a panel to an independent laboratory, we take part in that testing, and we publish what comes back. Neither kind traces back to the specific vial in your order, and anyone who tells you a published certificate proves what is in the vial you received is claiming more than this kind of testing can do. Per-lot verification is where we want to be, and we are working toward it. Read the document yourself against the checklist above rather than taking a number on trust.

Related Resources

• How to Read a Peptide COA: Complete Guide
• Research-Grade vs Pharmaceutical-Grade Peptides
• NorthPeptide Test Results — every published lab result, with who commissioned it
• Browse NorthPeptide Products

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Written by NorthPeptide Research Team · For laboratory and research use only. Not for human consumption.

Written by NorthPeptide Research Team