Certificate of Analysis

A Certificate of Analysis is a laboratory report on a specific batch. It states what was tested, by what method, and what the result was. A good one is signed, dated, names the lab, and identifies the batch it belongs to. It is evidence about one sample at one moment, and that framing is the key to reading it correctly.

Nearly every problem with COAs in this space comes from treating a batch document as a product guarantee.

Purity and identity are two different tests

Purity asks what fraction of the material is the thing it is supposed to be, and is usually reported from HPLC, high-performance liquid chromatography. The sample is separated into its components and the target peak is measured against everything else. A result of 99 percent means the target accounted for 99 percent of what the detector saw.

Identity asks whether the main peak is actually the molecule claimed, and needs mass spectrometry. It measures molecular weight, which is how you confirm the sequence is the one on the label rather than a different peptide of similar size.

These answer different questions and one does not substitute for the other. A certificate reporting only HPLC purity is telling you the sample was mostly one thing. It is not telling you what that thing was.

What the number does not cover

An HPLC purity figure describes what the detector responded to under the conditions used. Several categories of contaminant are routinely outside that.

• Residual solvents from synthesis, which need their own test.
• Endotoxin, a bacterial breakdown product that is not a peptide, does not show as an impurity peak, and matters specifically for injectables. It is measured separately, usually by LAL assay.
• Sterility, which is a microbiological test and not a chromatographic one.
• Water content and net peptide content. Lyophilised powder includes counter-ions and residual moisture, so a vial labelled 5 mg may hold less than 5 mg of peptide. Net peptide content is the figure that answers this and it is frequently absent.

A certificate can therefore report 99 percent purity on material that is not sterile, carries endotoxin, and contains meaningfully less peptide than the label says. Each of those is a separate test and each is separately absent or present.

Who tested it

The question that decides how much a certificate is worth is who ran the assay. A COA produced by the seller, or by a lab the seller commissioned and paid, is not independent of the sale. Third-party testing, where an independent laboratory receives the sample and reports directly, is the version that carries weight.

Two practical checks. Does the batch or lot number on the certificate match the number on the vial in front of you, and is the document dated. A certificate for a different batch is not evidence about the one you have, and an undated certificate cannot be placed against a manufacturing date at all.

A PDF with no lab name, no batch number and no date cannot be checked against anything, and does not do what a certificate is for.

What it still cannot tell you

Even a complete, third-party certificate is silent on the things that determine what is in the vial by the time it reaches you. It says nothing about how the material was stored or shipped, whether it was held cold, or how it was handled after the sample was drawn. It says nothing about stability over time, because it is a snapshot. And it says nothing about whether the compound does anything, which is a question about clinical evidence and not about chemistry.

That last distinction is worth holding onto. A certificate is a manufacturing document. It speaks to what a substance is, never to what it does. Those are the two axes this site keeps separate: the compound library grades how much research exists behind each compound, which is an entirely different question from whether a given vial contains what the label claims.

Related terms: HPLC, mass spectrometry, research chemical, lyophilized.