A Certificate of Analysis (COA) is the lab report that says what’s in a vial, how much of it there is, and how pure it is. Almost every peptide seller posts one now, which means the COA itself proves nothing unless you know how to read it. This guide walks through every section using a fictional sample and shows you how to spot a COA that doesn’t hold up.
Key takeaways
- A useful COA is batch-specific, recent, and from a named independent lab.
- Purity (HPLC) and identity (mass spec) answer two different questions. You want both.
- “99% pure” doesn’t mean 99% of the powder is peptide. Net peptide content is usually lower.
- If the lot number on the COA doesn’t match your vial, the COA isn’t for your product.
Sample COA (fictional, for teaching only)
| Product | Example Peptide-X, 10 mg lyophilized |
|---|---|
| Lot / batch | EX-26-0117 |
| Manufacture date | 2026-02-10 |
| Test date | 2026-03-02 |
| Testing lab | Sample Analytical Labs (independent), report #SAL-44821 |
| Appearance | White lyophilized powder. Conforms. |
| Purity (HPLC, 220 nm) | 99.1% |
| Identity (ESI-MS) | Observed 1419.6 Da, expected 1419.5 Da. Conforms. |
| Net peptide content | 84.3% |
| Quantity per vial | 10.2 mg |
| Endotoxin (LAL) | <0.5 EU/mg |
| Water content | 4.1% |
Section by section
1. Product name and lot number
The lot (or batch) number ties the report to one production run. It should be printed on your vial or box and match the COA exactly. A COA without a lot number can’t be tied to anything.
2. Dates
Look at both the manufacture and test dates. A recent test is better. If a seller shows the same COA from years ago for every batch they’ve sold since, it tells you nothing about the vial in your hands.
3. Testing lab
An independent, named lab is more trustworthy than an in-house report from the seller. Many labs issue a report number or QR code you can check on their website. If you can’t verify the report with the lab that supposedly issued it, treat it as unverified.
4. Purity by HPLC
High-performance liquid chromatography (HPLC) pushes the dissolved sample through a column that separates molecules. A detector records each one as a peak on a chart called a chromatogram. Purity is the size of the main peak as a percentage of all the peaks.
- Research-grade peptides typically aim for 98% or higher.
- A good COA includes the actual chromatogram, not just a number.
- Small extra peaks are usually related impurities, such as peptides missing one amino acid.
5. Identity by mass spectrometry
Here’s the catch with HPLC: it tells you that one main thing is in the vial, not that it’s the right thing. Mass spectrometry (MS) measures the molecular weight and compares it with the expected weight of the target peptide. A match within a small margin confirms identity.
A COA with purity but no identity test is incomplete. A vial could be 99% pure of the wrong compound.
6. Net peptide content
This is the line most people skip. Lyophilized peptides aren’t 100% peptide by weight. They also contain water and counter-ions (often trifluoroacetate or acetate salts left over from manufacturing). Net peptide content, commonly 70–90%, is the share of the powder that is actually peptide.
So a vial can be “99% pure” and still contain less peptide than its label weight suggests. That matters for anyone doing concentration math; see our Peptide Math page.
7. Quantity
Confirms the vial contains the labeled amount. Underfilled vials are one of the most common problems found when independent testers check research products.
8. Endotoxin
Endotoxins are fragments of bacterial cell walls that can cause fever and inflammation. The LAL test reports them in endotoxin units (EU) per mg. Not every research COA includes it, but it’s a strong sign of a careful supplier when it does.
9. Other tests you may see
- Sterility: checks for living microbes.
- Heavy metals: checks for lead, mercury and similar contaminants.
- Water content: usually by Karl Fischer titration.
Red flags of a fake or useless COA
- No lot number, or a lot number that doesn’t match the vial
- No lab name, or a lab you can’t find online
- Purity listed with no chromatogram and no identity test
- The same COA used for multiple products or years of batches
- Blurry, cropped or edited-looking images; mismatched fonts
- Round, too-perfect numbers like “100.00% purity”
- The lab says it has no record of the report number
COA checklist
- Lot number matches my vial
- Tested within a reasonable time of manufacture
- Named, independent lab I can verify
- HPLC purity with chromatogram, 98%+
- Mass spec identity that matches the expected weight
- Quantity per vial at or above label
- Bonus: net peptide content, endotoxin, sterility
For the bigger picture on choosing a supplier, read how to spot a sketchy peptide vendor and our Reading Labels page.
Frequently asked questions
What does COA stand for?
Certificate of Analysis: a lab report listing the tests run on a specific batch of product and the results.
What purity should a research peptide have?
Research-grade peptides are typically expected to test at 98% or higher by HPLC, along with a mass spec result confirming identity.
What is the difference between purity and net peptide content?
Purity is the share of the peptide material that is the target compound. Net peptide content is the share of the total powder weight that is peptide at all, after water and salts.
How do I verify a COA is real?
Check that the lot number matches your vial, then contact or search the issuing lab using the report number. Many labs offer online verification.
Medical disclaimer: Pep Guide is for educational purposes only. It is not medical advice, diagnosis or treatment. Research changes over time. Talk to a licensed healthcare provider before starting, stopping or changing any medication or compound.