How to read a peptide Certificate of Analysis
A Certificate of Analysis reports what a laboratory measured on one specific batch, against limits set before the sample was run. Read it in this order: find the batch number and match it to your vial, check that every result sits beside a specification, then check that the purity figure names the method that produced it. If any of those three is missing, the rest of the document does not matter.
This page explains each field in plain terms and lists the red flags worth walking away from. It applies to any vendor's certificate, not only ours. Our own published certificates are on the lab results page, where you can check every claim below against a real document.
What each field means
Batch or lot number
The identifier for the specific quantity of material this certificate describes. It is the only field that ties the document to a physical vial.
What to check: Check it matches the lot printed on your vial. A certificate you cannot tie to a lot is a brochure.
Test, method, specification, result
Four columns that belong together. The test names the determination, the method names how it was measured, the specification is the limit agreed in advance, and the result is what came back.
What to check: A result with no specification next to it cannot pass or fail anything. A specification written after the result is not a specification.
Purity
For a peptide, almost always the target peak as a percentage of total peak area in a reversed-phase HPLC run at a stated wavelength.
What to check: Look for the wavelength and the column. Purity quoted with no method attached is a number with no units.
Date of analysis and date of issue
When the sample was actually run, and when the document was produced. They are not the same date and the gap matters.
What to check: An analysis date far older than the batch in circulation means you are reading a certificate for material that has since been replaced.
Identity confirmation
Usually a measured molecular mass compared against the theoretical mass of the sequence, by mass spectrometry.
What to check: Purity without identity tells you the vial contains one thing in high proportion. It does not tell you it is the right thing.
Who performed the analysis
The laboratory that ran the sample, which is separate from the company that published the document.
What to check: A certificate issued and signed by the seller's own quality department is a self-assessment. That is not automatically dishonest, but it is not independent evidence either.
What a certificate cannot tell you
A purity percentage describes the sample that was analysed. It does not describe the vial in your hand unless the lot numbers match, and it does not describe how the material was handled after it left the laboratory. Heat and repeated freeze-thaw cycles degrade peptides in ways no certificate can anticipate, which is why the published storage conditions are part of the evidence rather than an afterthought.
It also carries no regulatory weight. Where a method cites a pharmacopoeial chapter, that names the procedure followed for that determination, not a statement of compendial compliance for the product. The chapters cited across our own certificates are USP <61>, USP <71>, USP <232>, USP <467>, USP <788>.
Red flags on any vendor's certificate
- ●No batch or lot number anywhere on the document, so it cannot be matched to anything you were sent.
- ●The same certificate reused across batches, sometimes with only the date changed.
- ●A purity figure with no method, no wavelength and no column stated.
- ●A result column with no specification column, so nothing was ever defined as passing.
- ●An image-only file with no selectable text, which is the usual sign a number has been edited over the original.
- ●An unnamed laboratory, or a lab named only as "third-party" with no way to verify the result independently.
- ●Purity claimed to three decimal places on a method that does not resolve to three decimal places.
- ●Identity asserted in prose rather than reported as a measured mass against a theoretical mass.
- ●A certificate that arrives in the box rather than being published, so it can never be checked against anything.
Common questions
What does 99 percent purity on a peptide COA actually mean?
It normally means the target peak accounted for 99 percent of the total peak area in a reversed-phase HPLC run, at a stated detection wavelength. It is a proportion of what the detector saw, not a proportion of the mass in the vial. Water, salt and counter-ion do not absorb at those wavelengths and so are not counted at all, which is why water content and counter-ion content are reported as separate determinations.
Is a Certificate of Analysis proof that a peptide is safe?
No. A certificate reports analytical results against specifications. It is not a safety assessment, not a regulatory approval and not a fitness-for-purpose claim. Research material sold for laboratory use is not approved by any regulator for human use, and a certificate does not change that.
How do I know a Certificate of Analysis has not been edited?
Three checks catch most of it. First, the certificate should be published at a stable address rather than sent to you as a file, so the same document is visible to everyone. Second, the batch number on it should match the lot on your vial. Third, the analytical result should be internally consistent: a stated purity should agree with the chromatogram area, and the reported mass should agree with the theoretical mass of the sequence.
Why do different certificates for the same compound show different tests?
Because the panel follows the molecule. A small synthetic peptide is characterised by reversed-phase HPLC and mass spectrometry. A folded protein is denatured by those conditions, so its purity figure comes from size-exclusion monomer content instead. A metal complex adds elemental analysis. A panel identical across every product would be a sign the panel is decorative.
What is the difference between an in-house COA and a third-party COA?
An in-house certificate is produced by the seller's own quality function. A third-party certificate reports analysis performed by an independent laboratory with no commercial interest in the result. Both can be accurate. Only the second one is evidence, because only the second one was produced by somebody with nothing to gain from the number.
The rest of the evidence
Each page answers one part of the same question. None of them asks you to take a claim on trust.
The procedures that decide whether a batch is released, held or withdrawn.
Every technique on the certificates, what it proves, and what it cannot.
How the vial in your hand connects back to the batch that was tested.
How material is made, how a supplier is qualified, and what changes trigger a re-test.
Published storage conditions, shelf life, and what degrades material fastest.
For research and laboratory use only. All Lyze Labs compounds are sold as research reference material, not for human or veterinary use. Nothing on this page is medical advice or a regulatory approval of any kind.