Reference
How to read a certificate of analysis
A certificate of analysis is a laboratory’s report on one sample it was sent. Knowing which questions it answers — and which it silently does not — is most of what separates evidence from decoration.
What a certificate actually is
A certificate of analysis, usually shortened to COA, is a document issued by an analytical laboratory recording what it measured in a specific sample on a specific date. It is a record of one test, on one sample, by one laboratory. It is not a statement about a product line, a supplier, or a vial that was never tested.
That distinction is the single most useful thing to hold on to. Everything below is really a way of asking the same question: does this document describe the thing I am being sold?
The fields, and what each one is for
The laboratory
The name of the laboratory that ran the test, not the supplier who commissioned it. A certificate with no laboratory named on it is not a certificate. An independent laboratory is one with no stake in the result; a supplier’s own in-house testing is not worthless, but it is a different kind of claim and should be labelled as such.
The client
Who submitted the sample. This matters more than it looks: if the client name on the report is not the supplier showing it to you, they are showing you somebody else’s test. That is common, and it is not automatically dishonest — but a report commissioned by a different company tells you about that company’s batch, not this one.
The report or task number
The laboratory’s own reference for the job. It is what makes the report checkable: without it there is nothing to look up. Treat a certificate with no reference number as an image rather than a document.
The sample name, and the batch
What the laboratory was told the sample was, and which production batch it came from. The batch field is the link between the tested sample and the vial in front of you. When it is blank — and it often is — the report still tells you what the laboratory found, but it cannot tell you that your vial came from the same material.
The method
How the measurement was made. Purity is normally by reversed-phase high performance liquid chromatography (HPLC); identity is normally by mass spectrometry. A purity figure quoted with no method attached is a number without a unit. What that HPLC figure measures is worth understanding separately, because it is narrower than most people assume.
Purity
Usually a percentage of the total chromatographic peak area. Read it as “of the material this method can see, this proportion was the target peptide” — not “this proportion of the vial is peptide”. Those are different statements and the difference can be large.
Mass, or identity
The measured molecular weight, against the value expected from the sequence. This is the field that addresses identity: purity tells you the sample was mostly one thing, mass spectrometry addresses whether that thing is the compound named on the vial. A report with a purity figure and no mass confirmation has answered only half the question.
Content, or net peptide content
How much of the weighed powder is actually peptide, as opposed to counterion salt, residual water and other non-peptide mass. This is the field most often absent, and the one that governs whether a “10mg” vial contains ten milligrams of peptide or ten milligrams of powder containing rather less.
What a certificate does not tell you
Unless the report explicitly says otherwise, a standard peptide COA says nothing about:
- Sterility. Purity is not sterility. They are unrelated measurements.
- Endotoxin. Bacterial endotoxin is a separate assay and is rarely included.
- Heavy metals or residual solvents. Separate tests again.
- Your particular vial, unless the batch on the report matches the batch you received.
None of that makes a certificate less valuable. It makes it a specific piece of evidence rather than a general reassurance, which is the correct way to use it.
Things worth treating as warning signs
- No laboratory name, or a laboratory that cannot be found to exist.
- No report or task number, so nothing can be looked up.
- A purity figure with no stated method.
- A flat image of a certificate with every identifying field cropped or blurred out.
- The same certificate shown against several different compounds.
- A supplier who will show you a purity number but not the document behind it.
The step most people skip
A published certificate is a claim until you have checked it with the laboratory that issued it. Most reports carry a verification key for exactly this purpose, and the check takes about a minute — here is how it works.
