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What is a certificate of analysis for peptides?
The short answer
A certificate of analysis is a laboratory's signed record of what it measured in a specific sample: chromatographic purity, quantity in milligrams per vial, the identity basis, and the method used. It describes one vial from one lot on one date. It is evidence about that sample, not a quality guarantee covering everything a vendor sells.
In detail
A useful CoA answers four questions and says which of them it did not answer. How pure was the material, by what measurement. How much peptide the vial actually contained, against what the label claimed. Whether identity was established presumptively or confirmed. And which method produced those numbers, in a version you can look up.
What a CoA is not is a certificate about a vendor. It covers the sample the laboratory received, on the date stated. A vendor who tested one lot in March and still shows that document in December is telling you about March.
Any certificate that cannot be checked against the issuing laboratory's own records should be read as an unverified claim rather than evidence.
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