How to read a peptide certificate of analysis (COA)

What a COA is and what it is for

The COA (certificate of analysis) summarizes the tests run on one specific lot of a product. For research peptides it is the only way to know the vial contains what the label says, in the amount and purity it says.

It matters more than it seems: anti-doping analyses have found products sold online whose contents did not match their description, and FDA has warned about unapproved peptides with wrong doses or different salts.

The lines to check

1. Lot number. It must be the same as on your vial. A COA with no lot, or with a lot that is not yours, does not describe your product.
2. Laboratory and date. Who ran the analysis and when. An independent laboratory gives more confidence than the manufacturer itself.
3. Identity by mass spectrometry (MS). The measured mass must match the compound’s theoretical mass. It is the test that tells, for example, tirzepatide (about 4813 Da) from retatrutide (about 4731 Da).
4. Purity by HPLC. The percentage of the main peak against the total. Better if the chromatogram is shown, not just a number.
5. Peptide, salt and water content. A vial’s powder includes counter-ions (acetate, trifluoroacetate) and water; net content says how much is actually peptide.
6. Appearance. Color and form of the powder; GHK-Cu, for example, should look blue.

What "99% purity" means

HPLC purity says what share of what the method detects is the main peptide. It does not say how much peptide is in the vial: a powder can be 99% pure by HPLC and still contain a large share of salt and water. That is why purity and net content are different figures, and a good COA reports both.

It does not replace identity either: a very clean HPLC of the wrong molecule is still the wrong molecule. Mass spectrometry is what confirms what it is.

Signals in mass spectrometry

• +16 Da: one added oxygen; in peptides with methionine or tryptophan it usually means oxidation.
• −42 Da: a missing acetyl group, as in a non-acetylated TB-500 fragment.
• Masses of truncated sequences or molecules missing the fatty acid chain, in peptides such as tirzepatide or retatrutide.

Signs of an unreliable COA

• It has no lot number, or the same COA appears for every lot.
• It only says "99% purity" with no method, chromatogram or mass identity.
• It does not name the laboratory or the date of analysis.
• The reported mass does not match the compound.

CaribePeptides COAs

We publish certificates by product and lot in the COA library, where you can open each PDF. Each product page shows whether the current lot’s certificate is published, so you can compare the lot number before you order.