Start with what the document actually proves
A certificate of analysis proves one thing: a specific lab measured a specific sample on a specific date. It does not prove that the vial in your hand came from that sample. That single gap is where most bad peptide purchases happen.
Before reading a single number, check three fields: the lab name, the sample identifier, and the test date. If any of those are missing or generic, the document is marketing collateral. Our third-party COA verification service exists for exactly this case.
The purity number is meaningless without the chromatogram
A COA that says "99.2% purity" with no chromatogram attached tells you nothing. Purity by HPLC is an area-percent calculation, and that percentage depends entirely on how the method was run and where the integration lines were drawn.
What to look for on the chromatogram:
| Feature | Healthy sample | Warning sign |
|---|---|---|
| Main peak shape | Sharp, symmetrical | Broad, shouldered, or split |
| Baseline | Flat before and after the peak | Drifting or noisy |
| Run length | Long enough for late-eluting impurities | Truncated right after the main peak |
| Impurity peaks | Small, resolved, quantified | Unlabeled or cropped out of the image |
Identity is a separate test from purity
Purity tells you how much of the sample is one compound. It does not tell you which compound. Identity confirmation requires mass spectrometry, and the COA should list the observed mass against the theoretical mass for the sequence.
If a COA reports purity but no mass confirmation, you have a document that says "this vial contains 99% of something." We run both together in mass spec identity confirmation for that reason.
