Does a peptide COA show how much peptide is in the vial?
Short answer · as of 2026-10-05
Only if it reports a content (assay) result, and even then it describes the sample tested. EMA's synthetic-peptide guideline treats impurities and assay as separate tests, and expresses assay limits on a counter-ion-free, anhydrous basis. A purity percentage alone does not tell you milligrams of peptide, and a result for a bulk lot does not by itself show the fill of a vial.
By Peptide Industry Gossip · Published · General explanation, not legal or medical advice. Disclaimer.
Purity and content are different results
Purity describes how much of the detected material is not the main peptide, controlled in EMA's guideline as total and individual impurities. Assay describes how much peptide is present. EMA lists liquid chromatography, amino acid analysis, nitrogen analysis and qNMR as ways to assay content.
Why the two numbers diverge
EMA expresses assay limits on a counter-ion-free, anhydrous basis, and lists water content and counter-ion content as separate items. Our inference: a freeze-dried powder includes water and counter-ion, so its peptide content is below its weight, and a purity figure cannot be converted into milligrams.
What to look for on the report
- A line labeled content, net peptide content or assay, with a unit, a method and a limit.
- Water content and counter-ion lines, which explain the gap between weight and peptide.
- The sample and lot the result applies to, and whether it is a bulk lot or a filled vial.
What a result cannot show
- Whether a vial you hold contains the amount on its label. That needs a result for that vial or lot.
- Anything about tests the report does not list.
Sources
- EMA, Guideline on development and manufacture of synthetic peptides (adopted Dec. 4, 2025)
- WHO, Model certificate of analysis