HPLC Purity & COAs: How to Read a Peptide Certificate
Two questions decide whether a research peptide is worth using: how pure is it, and is it actually the molecule on the label? They sound like the same question. They aren't. A Certificate of Analysis answers both with independent lab data, and learning to read one is the single best habit a buyer can build.
Purity and identity are not the same thing
Purity asks: of everything in this vial, how much is the target peptide? Identity asks a different thing entirely — is the main component even the right molecule? You can have a very pure sample of the wrong compound. That's why the two tests below work together.
What ≥99% HPLC actually means
High-Performance Liquid Chromatography separates a sample into its components and measures each as a percentage of the whole. A result of ≥99% means the target peptide makes up at least 99% of the material, with everything else under 1%. On the chromatogram, that's one big peak and a few tiny ones.
Why mass spec matters just as much
HPLC tells you how pure the sample is. Mass spectrometry tells you what it is — by measuring the molecule's mass and checking it against the expected value. Purity without identity is half a story. A COA worth trusting reports both.
How to read a COA
- Batch / lot number — it should match the vial in your hand.
- HPLC purity vs. the stated specification (e.g. ≥99%).
- Mass spec result against the expected molecular weight.
- Testing lab and date — independent and recent is better.
- A clear pass/fail per analyte.
Red flags
- A purity number with no chromatogram or MS to back it up.
- No batch number, so you can't tie the report to your vial.
- A COA that never names the testing lab or date.
Frequently Asked Questions
What does ≥99% HPLC purity mean?
It means the target peptide is at least 99% of the material in the vial, with impurities under 1%, as measured by High-Performance Liquid Chromatography.
Why does a COA include mass spectrometry?
HPLC measures purity; mass spec confirms identity by checking the molecule's measured mass against its expected molecular weight. You want both.
How do I know a COA matches my vial?
Check that the batch or lot number on the certificate matches the number printed on your vial. If it doesn't, the report doesn't describe what you received.
