Verification
How to read a COA
A Certificate of Analysis (COA) is the lab report that says what's actually in a vial — what the compound is and how pure it is. This is a plain-language tour of each part, plus a checklist for telling a trustworthy COA from a meaningless one.
What a COA is
It's an independent lab's measured findings for a specific batch of material: its identity (is it really the peptide on the label?) and its purity (how much of it is the target compound?). A COA is only as good as the lab behind it and whether its batch matches the vial in your hand.
The parts of a COA
- IdentityWhat the compound is, confirmed by mass spectrometry (often written LC-MS or MS). The measured molecular weight should match the expected weight of the peptide.
- PurityHow much of the material is the target peptide, measured by HPLC and given as a percentage (for example 98.6%). The remainder is water, salts, or related impurities.
- Net contentThe actual mass of peptide present. It can be less than the gross vial weight, because water and counter-ions add weight — this is what the purity-adjusted calculator accounts for.
- Batch / lot & dateThe batch or lot number and test date. These must match the number printed on your vial — a COA for a different lot tells you nothing about yours.
- Lab & accreditationWho did the testing. The strongest COAs come from an independent, accredited lab (ISO 17025 / A2LA) whose accreditation scope actually covers peptide purity testing.
A trustworthy-COA checklist
Tick what your COA has. The more it covers, the more weight it carries.
Checklist0 / 7
Red flags
- No lab name, or a report the seller produced themselves with no traceable source.
- A lot number that doesn't match your vial — or no lot number at all.
- An image of a COA with nothing that lets you verify it independently.
- Accreditation claimed but not actually held, or held for a scope that doesn't include peptides.
Common questions
What's the difference between HPLC and LC-MS on a COA?
HPLC measures purity — how much of the sample is the target compound. LC-MS (mass spectrometry) confirms identity — that the compound's measured mass matches the expected peptide. Good COAs include both.
What is "net peptide content"?
The actual mass of peptide in the vial. Because water, salts, and counter-ions add weight, net peptide content is often a bit below the gross labeled mass.
What is ISO 17025 / A2LA accreditation?
A formal standard for testing-lab competence; A2LA is one body that grants it. It only matters if the lab's accredited scope actually covers the test in question — accreditation for one method doesn't certify all of them.
Can I trust a COA the seller provides?
Only if it's traceable to an independent lab and the batch matches your vial. A seller-generated report with no verifiable lab behind it isn't a COA in any meaningful sense.
Want the longer version? Our sister site has a full guide to verifying a COA.