How to Read a Peptide Certificate of Analysis (COA)
A Certificate of Analysis (COA) is the single most useful document for judging a research peptide's quality — if you know what to look at. This guide breaks down the parts that matter and the red flags that do not.
What a COA is
A COA is a lab report for a specific batch of product. A good one answers two questions: is this actually the compound it claims to be (identity), and how pure is it (purity). Everything else is supporting detail.
Purity — the HPLC number
Purity is usually measured by HPLC (high-performance liquid chromatography) and reported as a percentage — for research peptides you will commonly see figures like 98–99%+. HPLC separates the sample into its components; the peptide's peak area relative to everything else gives the purity percentage. Higher is better, and the chromatogram itself (the trace) is worth a look if provided.
Identity — mass spectrometry
Mass spec (MS) confirms the compound's molecular weight, verifying you have the right peptide and not a mislabeled or substituted one. A COA that reports a measured mass matching the expected mass is doing its most important job.
Batch matching
The COA should correspond to the specific batch or lot of the vial you received — not a generic sample. Reputable suppliers tie each product to its own batch COA, sometimes via a QR code or a lookup on their site, so you can verify the exact vial in your hand.
Third-party vs in-house testing
An in-house COA is better than nothing, but independent third-party testing carries more weight because the lab has no incentive to inflate the result. The strongest signal is a supplier that publishes batch-level COAs and welcomes independent verification.
Red flags
No COA at all; a single generic COA reused across every product; a COA with no batch/lot number; purity claims with no chromatogram or mass-spec data behind them; or a document that cannot be matched to the vial you actually received.
Key takeaways
- A COA answers two questions: identity (mass spec) and purity (HPLC %).
- The COA should match your specific batch/lot — not be a generic sample.
- Independent third-party testing beats in-house claims.
- No batch number, no chromatogram, or one reused COA for everything are red flags.
