A certificate of analysis (COA) is a lab report showing what is in a specific batch of a product. For peptides, it is the main way to check that a vial contains the right compound, in the right amount, without too much of anything else. Two vials with identical labels can be very different, so the COA is worth a few minutes of your time.
What a good COA includes
| Section | What it tells you | What to look for |
|---|---|---|
| Compound name | What was tested | Matches your vial exactly |
| Batch or lot number | Which production run was tested | Matches the number printed on your vial |
| Testing lab | Who did the testing | An independent third-party lab, not only the seller |
| Test date | When it was tested | Recent, and after the batch was made |
| Identity (mass spectrometry) | Whether the compound is what it claims to be | Observed molecular weight matches the expected value |
| Purity (HPLC) | How much of the material is the target peptide | Usually 98% or higher, with the chromatogram shown |
| Quantity or content | How many mg are actually in the vial | Close to the labeled amount |
Identity: is it the right compound?
Mass spectrometry (often written MS, LC-MS or MALDI) weighs the molecules in the sample. Every peptide has a known molecular weight, so the report should list the expected mass and the observed mass. They should match closely. Without an identity test, a high purity number only tells you the sample is pure, not that it is the right substance.
Purity: how clean is it?
HPLC (high-performance liquid chromatography) separates the sample into its parts. The result is a graph called a chromatogram, with one tall main peak for the peptide and small peaks for impurities. Purity is the main peak’s share of the total. Look for the chromatogram itself, not just a percentage.
Quantity: is the full amount there?
Purity and quantity are different things. A vial can be 99% pure and still hold 3.5 mg instead of 5 mg. A quantity (or “net content”) test measures the actual mg per vial. This matters directly for dosing: if the vial is under-filled, every calculated dose will be too low.
Extra tests worth seeing
- Endotoxin: checks for bacterial toxins that can cause fever and reactions.
- Sterility: checks for live bacteria or fungi.
- Heavy metals: checks for lead, mercury, arsenic and cadmium.
- Residual solvents or TFA: leftovers from manufacturing.
Red flags
- No batch number, or a batch number that does not match your vial.
- A COA from the seller only, with no independent lab named.
- The same COA reused across many batches or for years.
- Purity listed with no chromatogram, or identity not tested at all.
- Suspiciously perfect numbers, such as 99.9% purity on everything.
- Signs of editing: mismatched fonts, blurred areas, missing lab contact details.
- A report you cannot verify with the lab.
How to verify a COA
- Match the compound name and batch number to your vial.
- Check that the lab is independent and that it exists, with a real website and contact details.
- Use the lab’s verification tool if it offers one. Many independent labs print a code or QR code that lets you confirm the report online.
- Check the date is recent and after the batch was made.
- When in doubt, ask the seller for the original report or send a sample for your own testing.
Quick checklist
- Right compound name
- Batch number matches your vial
- Independent lab, verifiable
- Recent test date
- Identity confirmed by mass spectrometry
- Purity by HPLC, with chromatogram
- Quantity close to the label
- Bonus: endotoxin, sterility and heavy metals