How to Read a Peptide Certificate of Analysis
What a COA actually reports, what it does not, and how to check one against the vial in front of you.
What a certificate is
A certificate of analysis is a laboratory's report on one specific lot of material. It is not a statement about the product in general, and it is not transferable between lots. Two vials of the same compound from the same supplier can have different certificates, because they came from different synthesis runs.
That is the first thing to check: the lot number on the certificate must match the lot number on the vial in front of you. A certificate for a different lot tells you nothing about what you are holding.
What it should contain
A usable certificate names all of the following. If any are missing, the document is decorative rather than informative.
- The compound, and ideally its CAS number
- The lot or batch number, matching the vial
- The date of analysis
- The testing laboratory — a named lab, not just the seller
- The method used for each measurement, e.g. RP-HPLC, ESI-MS
- A purity figure, with the chromatogram it came from
- An identity confirmation, usually a measured mass against the expected molecular weight
How to check it against the vial
Compare the lot number first. Then compare the measured mass on the certificate against the compound's published molecular weight — they should agree to within about a unit. If the certificate reports a mass that does not match the formula, that is a substantive problem, not a rounding error.
Purity and identity are separate questions and both should be answered. A certificate that gives a purity percentage with no identity confirmation has established that the vial contains 99% of something.
What a certificate does not tell you
A certificate establishes composition. It does not establish sterility, endotoxin levels, or that the material is appropriate for any particular use. Those are separate tests, reported separately when they are done at all.
It is also not a safety document. A certificate confirms what is in the vial. It is not evidence that the material is safe or suitable for any use outside a laboratory.
We do not provide dosing, reconstitution, administration or protocol guidance for any compound, and we will not answer questions about using a product on a person or an animal. See our Research Use Only Policy.