How to Read a Peptide Certificate of Analysis (COA)

A Certificate of Analysis (COA) is the single most important piece of documentation a research peptide supplier can provide. It is the batch-level proof that the vial in your hand matches the sequence and purity claimed on the label. Here is how to read one critically.

What a legitimate COA contains

• Batch or lot number, matching the vial label exactly.
• Test date and lab name, from an independent third-party analytical laboratory (not the supplier's in-house claim).
• HPLC chromatogram with a purity percentage and clear integration of the main peak vs. impurity peaks.
• Mass spectrometry (typically ESI-MS or MALDI-TOF) confirming the observed molecular weight matches theoretical within instrument tolerance.
• Endotoxin (LAL) result in EU/mg — commonly overlooked but critical for downstream cell-culture work.
• Residual solvent screen (often GC or NMR) for TFA, acetonitrile, and other synthesis-stage solvents.

Red flags

1. No chromatogram, just a number. A stated purity without the underlying HPLC trace is not verifiable.
2. Lab logo missing or unlisted lab. Reputable third-party analytical labs are named and reachable.
3. Batch number does not match the vial. Ask why — legitimate suppliers can explain the numbering scheme.
4. No endotoxin data. Common gap. Endotoxin contamination invalidates most cell-based assays.

The bottom line

A COA is the accountability document. If a supplier cannot produce one on request, or the COA cannot be tied back to a specific batch number, treat the material as unverified.