# Reading a peptide vendor’s certificate of analysis

Three checks catch most bad certificates of analysis (COAs) in the research-peptide market:

1. Match the lot number. The COA is only evidence for the batch whose number is printed on it. If the certificate’s lot does not match the vial you received, it is decoration.
2. Check the test date. A purity percentage without a recent test date says nothing about what is shipping today. Reputable vendors re-test and re-publish; resellers recycle the same PDF for years.
3. Look for a named third-party lab. In-house HPLC printouts are better than nothing, but a named independent lab with contactable results is the standard that holds up.

Also worth noting: purity is measured per batch, not per vendor. A vendor that tested 99.2% in March is not automatically 99.2% in October — the question is whether later batches carry later certificates.

Dated purity records, per-mg price comparisons and a public vendor-warnings list are maintained at Peptide Compare.

(Informational comparison content only — not medical advice.)