A certificate of analysis (CoA) is a laboratory report describing what was actually found in one specific batch of a research-use-only compound. In the research-peptide market it is the single most useful document a buyer can read — and also the easiest thing to fake with a decorative PDF. A real CoA is evidence; a fake one is decoration that happens to be shaped like evidence. This guide walks through every element a genuine peptide certificate of analysis should contain, how to read the purity and identity results, and the specific red flags that separate third-party testing from theatre.
What should a peptide CoA contain?
A credible peptide CoA is built from a small number of non-negotiable fields. Each one answers a different question, and each one has a matching failure mode. Read the document field by field rather than trusting the headline percentage.
| Field | What it proves | Red flag if missing or vague |
|---|---|---|
| Named laboratory | An identifiable, independent lab ran the analysis | “Tested by a US third-party lab” with no name |
| Batch / lot number | The result describes your vial, not a generic sample | One certificate reused across every product |
| Date of analysis | Results describe the batch at a point in time | Undated, or several years old |
| Purity method + result | How clean the peptide is, with the HPLC trace behind it | A percentage with no chromatogram attached |
| Identity method + result | The molecule is the one on the label (mass spectrometry) | Purity shown, identity absent |
| Verification mechanism | The document can be authenticated at the lab's source | A code or QR that resolves nowhere |
If any of the first three are missing, you are not really looking at a batch-level report — see batch-level vs generic CoAs for why a lot number is the difference between a document about your vial and marketing wallpaper.
How do you read the purity result on a CoA?
Purity is almost always an HPLC (High-Performance Liquid Chromatography) figure — for example 99.0%. It means the target peptide's peak accounts for 99% of the total detected signal, and everything else (impurities, related substances, breakdown products) makes up the remaining 1%. The number is a summary; the real evidence is the chromatogram — the plotted trace itself. A bare percentage with no trace behind it is a weak signal, because you cannot see how the lab reached it, whether the baseline was stable, or whether the main peak was cleanly separated from its neighbours.
A worked example: a CoA states 98.7% purity and attaches a chromatogram with one tall, well-separated main peak and two tiny peaks near the baseline. That is internally consistent and readable. A CoA that states 99.9% but shows no trace — or shows a trace whose peaks do not visibly match the claimed integration — has told you less than it appears to. For the full method, read what a purity percentage actually measures and how to read an HPLC chromatogram.
How does a CoA confirm identity?
Purity tells you the sample is clean. It does not tell you the clean substance is the peptide the label names. That is a separate question — identity — answered by a separate method: mass spectrometry (MS), often coupled as LC-MS. MS measures the compound's molecular mass and checks it against the expected value for the claimed peptide. A sample can be 99% pure and still be the wrong molecule, so a complete CoA pairs an HPLC purity result with an MS identity result. If a certificate shows only a purity figure, it has answered half the question. See HPLC vs mass spectrometry and how MS confirms identity for what each method can and cannot prove.
Is purity the same as net peptide content?
No — and confusing the two is one of the most common CoA misreadings. HPLC purity describes how clean the peptide fraction is relative to other peaks. Net peptide content describes how much of the vial's mass is actually peptide, because a freeze-dried peptide also carries water, residual salts (TFA or acetate) and counter-ions. A sample can be 99% pure by HPLC and still be a meaningful fraction water and salt by weight. Net content is measured separately (amino acid analysis or nitrogen determination) and reported as its own figure. Our guide on net peptide content vs purity covers the gap in detail.
How can you tell if a peptide CoA is fake?
Most fake or worthless certificates fail on the same handful of signals. Treat any of these as a reason to distrust the document until proven otherwise:
- No lab name, or a “lab” that cannot be found to exist anywhere outside the vendor's own site.
- A percentage with no chromatogram — a purity claim you cannot see the evidence for.
- One generic certificate linked from every product, with no batch number tying it to a specific lot.
- CoAs only “available by email on request” after purchase, rather than published up front.
- A verification code or QR that leads nowhere, or a portal you can never actually reach.
- Identity missing entirely — purity shown, but nothing confirming the molecule is what the label claims.
These overlap with the broader red flags in vendor transparency that lower a vendor's score on PeptideTrust.
How do you verify a CoA is real?
The strongest test is not reading the CoA — it is authenticating it at the source. The best certificates can be verified on the lab's own website, not just downloaded from the vendor. A verification code or QR that resolves on the lab's domain (Janoshik, MZ Biolabs, and similar independent labs publish such lookups) is very hard to fake, because it means the document exists in the lab's records, not only in the vendor's marketing folder. When PeptideTrust scores “CoA verifiable at source,” we test it by actually following the code — not by trusting that the mechanism exists. Step by step, see how to verify a CoA at the source and our list of independent peptide testing labs. Accreditation to ISO/IEC 17025 is a further strengthening signal.
Does a CoA prove a peptide is safe?
No. A purity-and-identity CoA describes composition — not sterility, not bacterial endotoxin load, and not safety. A solution can be 99% pure and the correct molecule while still being non-sterile or carrying endotoxins, because those are tested by different methods that most standard peptide CoAs exclude. Some vendors publish separate sterility and endotoxin (LAL) reports; many labs explicitly leave them off a purity CoA. Absence of that data is common — just understand that a purity CoA is not a sterility guarantee. See endotoxin and sterility testing. Nothing on a CoA, and nothing in this guide, is medical advice.
Once you can read a certificate of analysis, the PeptideTrust scoreboard shows which vendors actually publish one that survives this checklist — every score links to the exact document we checked. Our scoring methodology explains how each element above is weighted.