How to Read a Certificate of Analysis (CoA)

A Certificate of Analysis (CoA) is the document a supplier provides to show that a specific batch of peptide has been independently tested and meets its stated specification. It's the single most useful piece of documentation for judging research material — but only if you know how to read it. A logo and a "99%" figure alone mean very little without the underlying data behind them.

Batch and Identity Information

A meaningful CoA starts by identifying exactly what was tested: the peptide name, its molecular formula, molecular weight, and — critically — a batch or lot number that matches the label on the vial you received. If the lot number on the CoA doesn't match the vial, the certificate tells you nothing about the material in your hand. The test date should also be present, since peptide quality is a property of a specific batch at a specific time.

The Purity Section (HPLC)

Purity is normally determined by HPLC (high-performance liquid chromatography) and expressed as a percentage — the area of the target peptide's peak as a proportion of all peaks detected. A credible CoA shows the actual chromatogram, not just a number: a single dominant peak with minimal smaller peaks around it. Be cautious of any certificate that states a purity figure without showing the trace it came from.

The Identity Section (Mass Spectrometry)

HPLC tells you how pure the sample is, but not whether it's actually the right compound. That's what mass spectrometry (MS) confirms — it measures the molecular weight of the peptide and checks it against the expected value. A complete CoA pairs HPLC purity with MS identity, because a sample can be 99% pure and still be the wrong peptide. Seeing both is a strong signal the supplier is testing properly.

Red Flags

• No chromatogram — just a stated percentage with no visual trace to support it.
• No batch number, or one that doesn't match your vial.
• HPLC but no mass spec — purity without identity confirmation.
• No testing date or no name of the testing lab.
• A generic CoA reused across every product rather than being batch-specific.

For more on the two analytical methods a CoA relies on, see our guide to HPLC and mass spec testing, and our explainer on what a purity percentage actually means.