Guide
How to read a peptide Certificate of Analysis
A Certificate of Analysis is the only document that connects the vial in your hand to a measurement someone actually made. It is also the easiest document in this industry to fake, reuse, or quietly detach from the material it describes. This is what each part of one means and how to tell a real one from a decorative one.
What a COA actually is
A Certificate of Analysis is a report issued by an analytical laboratory describing tests run on a specific batch of material. It is not a licence, not an approval, and not a statement that anything is safe or effective. It says: on this date, this laboratory ran these methods on this sample, and these were the results.
The word that carries all the weight is batch. A certificate describes the material it was run against and nothing else. A certificate for a batch made last year tells you nothing about the vial that arrived today, however impressive the number on it.
The seven things worth checking
- A lot or batch number, and the same number physically on the vial you received. If the certificate names no lot, it cannot be tied to anything.
- The name of the laboratory, and whether that laboratory is independent of the seller. In-house testing is not third-party testing.
- The date the analysis was run. A certificate with no date cannot be checked against the age of your material.
- The methods used - typically HPLC for purity and mass spectrometry for identity. A number with no method behind it is a claim, not a measurement.
- An identity result as well as a purity result. Purity tells you how much of the sample is one substance. Identity tells you which substance. Purity alone does not establish that the vial contains what the label says.
- The actual chromatogram or spectrum, not only a summary table. The trace is the evidence; the table is somebody's reading of it.
- Whether the seller publishes it openly or sends it on request. A published certificate can be checked by anyone at any time, including after you have bought.
Purity, identity and mass - three different questions
These get conflated constantly, and they answer different things.
Identity asks whether the material is the compound named on the label. Mass spectrometry answers it by measuring molecular mass and comparing it to the expected value for that molecule. A pass here is usually reported as 'conforms'.
Purity asks what proportion of the sample is that compound rather than anything else. HPLC answers it by separating the components and measuring the area under each peak. This is where the 99-point-something figure comes from.
Mass or content asks how much peptide is actually in the vial. This is a separate measurement from purity, and it is the one most often missing. A vial can be 99% pure and contain considerably less peptide than the label claims, because purity is a ratio and content is a quantity.
How to read the purity number
A purity figure is the area of the main peak as a percentage of total peak area in the chromatogram. That definition matters, because it is relative. It does not count anything the method cannot see - salts, water and residual solvent typically do not appear in a UV chromatogram at all.
This is why net peptide content and purity are different numbers, and why a certificate reporting only purity is telling you less than it appears to. Neither figure is wrong; they answer different questions.
Ways a certificate can be misleading without being forged
- Reused across batches. One good result, published against everything that followed. The tell is a lot number that does not change, or none at all.
- Run on a different sample. A certificate for material the seller tested once, attached to stock bought later from somewhere else.
- Summary only. A tidy table with no chromatogram, so the peak integration cannot be checked.
- Cropped traces. A chromatogram cut so that only the region around the main peak is visible, hiding whatever eluted elsewhere.
- Testing by a lab nobody can identify. A logo is not an accreditation. The laboratory should be nameable and findable.
- Identity omitted. Purity reported, identity quietly absent.
How to verify one yourself
Read the lot number off the vial and find that exact lot on the seller's site. If the certificate lives behind an email request, ask why.
Check the date of analysis against when the material was made available. Check that the laboratory named is a real laboratory with a findable address.
Where a signed laboratory report exists, that is the authoritative document - a vendor's summary page is a convenience, not the evidence. Many analytical laboratories will confirm a report they issued if you contact them directly with the report number, which is worth doing for any certificate you are relying on.
What a certificate cannot tell you
A certificate is an analytical result, not a safety assessment. It does not establish that a material is sterile, that it is free of endotoxin, or that it is suitable for any purpose. Those are separate tests, and most peptide certificates do not include them.
It also says nothing about handling after the test. Storage, transport and reconstitution all happen afterwards.
Most importantly: a certificate is not an approval. Research peptides are supplied for laboratory use, are not approved by the FDA for human or veterinary use, and a certificate does not change that.
Common questions
What does 99% purity on a peptide COA actually mean?
It means the main peak accounted for 99% of the total peak area in the chromatogram - a ratio of that compound to other detected substances in the sample. It is not a statement of how much peptide is in the vial, which is a separate measurement called net peptide content.
What is the difference between HPLC and mass spectrometry on a COA?
HPLC separates the components of a sample and is used to measure purity. Mass spectrometry measures molecular mass and is used to confirm identity - that the material is the compound named. A complete certificate reports both, because purity alone does not establish what the substance is.
Is a Certificate of Analysis proof that a peptide is safe?
No. A COA reports analytical results for a batch. It is not a safety assessment and not an approval of any kind. It does not establish sterility or freedom from endotoxin unless those specific tests are listed, and research peptides are not approved for human or veterinary use.
How can I tell if a peptide COA is real?
Check that it names a specific lot number matching the vial, names an identifiable independent laboratory, carries a date of analysis, states the methods used, and includes the chromatogram rather than only a summary table. Certificates published openly against a lot number can be checked by anyone; certificates sent only on request cannot.
Should a COA be batch-specific?
Yes. A certificate describes the batch it was run against. A certificate reused across multiple batches, or one with no lot number at all, cannot be tied to the material you received.
Why do some vendors only send a COA on request?
There is no analytical reason to withhold one. A published certificate can be verified before purchase and re-checked afterwards; one supplied on request can be selected per enquiry, and cannot be compared against what other buyers were sent.
Check the evidence for a Causa lot
Our lot pages publish the available results for assayed batches. Request the original laboratory Certificate of Analysis using the lot number, and compare it with the material you are considering. Materials without a qualifying result are marked assay pending. A summary is not a substitute for the original laboratory report.
Related research documentation guides
Research use only. Not for human or veterinary use. This guide explains how to read an analytical document. It is not medical advice and not guidance on use.