How to read a peptide COA, line by line
A certificate of analysis is a lab's report on one specific sample. It answers two questions: is this the compound on the label, and how pure is it? Everything else on the page tells you whether you can trust those two answers.
1. Identity: is it the right molecule?
Identity is usually confirmed by mass spectrometry (MS). The report should list an expected molecular mass and an observed one, and they should match within the lab's stated tolerance. A COA that shows purity but no identity test has told you how clean the sample is without confirming what it is.
2. Purity: how much of the sample is that molecule?
Purity is usually measured by HPLC (high-performance liquid chromatography) and reported as a percentage of peak area. Look for the chromatogram, the trace with peaks. One dominant peak with small side peaks is normal. A bare "99%" with no chromatogram is a claim, not a measurement you can check.
3. Lot or batch number: is this report about your vial?
A COA describes one lot. The lot number on the report must match the lot number on the vial or label you receive. If a supplier shows the same COA for every order, month after month, it isn't describing what's in your box.
4. The lab: who tested it, and can they be checked?
- Independent or in-house? A report from the manufacturer's own lab is a self-assessment. An independent third-party lab has no stake in the outcome.
- Accreditation. Testing labs can be accredited to ISO/IEC 17025, the international standard for testing-lab competence. Accreditation covers specific methods, so check that the method on your COA is within the lab's accredited scope.
- Verifiable. Many labs let you confirm a report with them directly, by a verification code or by contacting them with the report number. A report the lab can't confirm is a document anyone could have made.
5. Dates: tested when?
Check the sample-received and report dates. A report dated long before the lot was supposedly produced can't be about that lot.
Red flags at a glance
| What you see | What it can mean |
|---|---|
| No lab name, or a lab you can't find | The report can't be checked |
| Lot number missing or different from your vial | The report isn't about your product |
| Purity figure but no chromatogram | Nothing to check the number against |
| Purity but no identity (MS) test | Clean, but possibly the wrong compound |
| The same COA shown across many months | One old test standing in for every lot since |
| Edited-looking PDF, mismatched fonts, no report ID | Possibly altered. Ask the lab to confirm it. |
Next: why "it's all the same batch" isn't enough.