How to read a peptide certificate of analysis

A certificate of analysis (COA) is a lab report on one batch of a product. For a peptide it should answer two questions: is this the right molecule, and how much of what is in the vial is that molecule. Everything else on the page is there to prove the report belongs to the vial in your hand.

What a complete COA contains

• The lab's name and contact details. An independent lab you can look up, not the seller's own letterhead.
• The product and the batch (lot) number. The batch number should match the one printed on the vial.
• The test date. A report from long before the batch was made cannot be about that batch.
• The methods used, usually HPLC for purity and mass spectrometry (MS) for identity.
• The results: purity as a percentage, the measured mass next to the expected mass, and the raw chromatogram or spectrum.
• A signature or verification code that lets you confirm the report with the lab.

Purity and identity are different tests

HPLC separates the contents of a sample and reports how much of the signal comes from the main peak. That gives a purity percentage, but HPLC alone does not prove the main peak is the peptide on the label. Mass spectrometry measures the mass of the molecules. If the measured mass matches the peptide's known mass, that confirms identity. A COA with only one of the two answers only one of the two questions. Our guide to HPLC and mass spec goes deeper.

Purity is not quantity

A vial can be 99% pure and still hold less peptide than the label says. Purity tells you what share of the peptide material is the right peptide. How much peptide is in the vial is a separate measurement, sometimes reported as net peptide content or quantity. Freeze-dried peptides also contain water and salts left over from manufacturing, which add weight without being peptide.

Seven checks that catch most bad COAs

1. The batch number on the COA matches the vial.
2. The lab exists, is independent of the seller, and lists the test on its own site or verifies the report on request.
3. The test date is after the batch was made and is not years old.
4. Both identity (MS) and purity (HPLC) are reported.
5. The raw chromatogram or spectrum is included, not just a number.
6. The same report is not reused across different peptides or batches. Reverse-image search catches many recycled COAs.
7. For injectable products, an endotoxin result is reported. Purity says nothing about bacterial contamination.

Looking up a batch

Codex Research Lab has a public batch verification page where you can enter a batch number and see its COA, and a COA checklist for going over a peptide certificate.