How to Read a Peptide Certificate of Analysis (COA)
A Certificate of Analysis (COA) is the single most important document attached to a research peptide — and also the most commonly faked. This guide explains exactly what each field on a peptide COA means, how to tell a legitimate third-party report from an in-house screenshot, and how to independently verify the result yourself.
If you only take one thing away: a COA you cannot independently verify is just a picture.
What a Certificate of Analysis Actually Is
A COA is a lab report documenting the analytical testing performed on a specific batch of a compound. For research peptides, a credible COA answers three questions:
- Identity — is this actually the peptide it claims to be?
- Purity — what percentage of the sample is the target peptide versus impurities?
- Traceability — which batch was tested, by which lab, and when?
A COA is batch-specific. A report for one lot does not certify a different lot, which is why batch numbers and test dates matter.
The Key Fields, Explained
Purity (%)
Reported purity is almost always measured by HPLC (High-Performance Liquid Chromatography). HPLC separates the sample into peaks; the target peptide peak is measured against impurity peaks, and the ratio is reported as a percentage. For research-grade material, 99%+ HPLC purity is the standard benchmark.
A purity figure with no testing method listed is a red flag — purity is meaningless without the method that produced it.
Mass / Molecular Weight
Many COAs include mass spectrometry (MS) confirmation. MS verifies the peptide’s molecular weight matches the expected value for that exact amino-acid sequence, confirming the lab tested the right molecule and not a similar one. Identity (MS) and purity (HPLC) are two different questions — strong COAs answer both.
Batch / Lot Number
This ties the report to a specific production run. If the batch on the COA doesn’t match the batch on the vial, the report doesn’t describe what you received.
Testing Laboratory
Note who ran the test. An independent third-party lab (such as Janoshik Analytical) provides materially stronger assurance than an in-house “self-tested” result, because the seller has no ability to edit a third party’s report.
Test Date
Peptides are tested per batch over time. A recent date tells you the lot is current; an old date may mean the inventory has turned over since testing.
The One Step Most Buyers Skip: Verification
Here is the difference between a transparent supplier and a convincing one. A legitimate third-party COA can be verified at the source. Janoshik, for example, issues every report with a unique key, and anyone can confirm the result at janoshik.com/verify/ by entering the task number and key.
If a supplier shows you a COA image but there is no way to confirm it on the testing lab’s own website, you are trusting a screenshot that could have been altered in any image editor. This is the most common form of COA fraud in the research peptide market.
How to verify in under a minute:
1. Find the task number and unique key on the COA.
2. Go to the testing lab’s official verification page.
3. Enter the details and confirm the purity, batch, and date match what the supplier showed you.
At PolixLabs, every tested lot links directly to its live verification — see our Lab Results page, where each compound carries a “Verify” link that takes you to Janoshik’s own site. The data you see is the data we report, and you never have to take our word for it.
Red Flags on a Peptide COA
- No testing method listed next to the purity figure.
- In-house testing only, with no independent lab named.
- No batch number, or a batch that doesn’t match the vial.
- No way to verify the report on the lab’s website.
- A placeholder or broken reference where the verification link should be — a sign of a template that was never properly filled in.
- One COA reused across every product, rather than a batch-specific report per compound.
Why This Matters for Research Integrity
Reproducible research depends on knowing what you actually put into an experiment. An unverified compound of unknown purity introduces a variable you can’t control or report. A verifiable COA isn’t bureaucracy — it’s the documentation that makes your results defensible.
Suppliers who publish independent, verifiable third-party COAs for every batch are signaling that they expect to be checked. That’s the standard worth holding the market to.
Frequently Asked Questions
What purity should a research peptide be?
99%+ by HPLC is the widely used benchmark for research-grade peptides. Always confirm the testing method is stated.
What’s the difference between HPLC and mass spectrometry on a COA?
HPLC measures purity (how much of the sample is the target peptide). Mass spectrometry confirms identity (that the molecule has the correct molecular weight). Strong COAs include both.
How do I know a COA is real and not edited?
Verify it on the testing laboratory’s own website using the report’s unique key or task number. If it can’t be verified at the source, treat it as unconfirmed.
Is an in-house COA good enough?
In-house testing is better than nothing, but a third-party COA from an independent lab is the stronger standard because the seller cannot alter the result.
PolixLabs publishes independent, third-party Janoshik certificates of analysis for every tested lot. Browse verified research peptides or confirm any result yourself on our Lab Results page. All products are for laboratory and research use only — not for human or animal consumption.