Two analytical methods dominate peptide quality testing: HPLC and mass spectrometry (MS). They answer different questions, and a trustworthy Certificate of Analysis reports both.
HPLC answers: “How pure is it?”
High-Performance Liquid Chromatography pushes a dissolved sample through a column that separates molecules by their chemical properties. Each component exits at a different time and is recorded as a peak on a chromatogram.
- A single, tall, sharp peak with little else means high purity.
- Extra peaks or shoulders indicate impurities or related species.
- Purity is reported as a percentage — the area of the main peak relative to the total.
What HPLC cannot do on its own is *prove the main peak is the peptide you ordered*. A pure sample of the wrong molecule would still show one clean peak.
Mass spectrometry answers: “What is it?”
Mass spectrometry ionizes the molecule and measures its mass-to-charge ratio, yielding a precise molecular mass. Comparing the observed mass to the theoretical mass of the intended peptide confirms identity.
- If observed mass = theoretical mass, the identity is confirmed.
- A mismatch suggests the wrong sequence, a modification, or contamination.
MS is the identity check that HPLC’s purity number relies on to be meaningful.
Why you need both
| Question | Method |
|---|---|
| How pure is the sample? | HPLC |
| Is it actually the right molecule? | Mass spectrometry |
Purity without identity is “very pure *something*.” Identity without purity is “the right molecule, mixed with who-knows-what.” Quality requires the pair.
Reading the results on a COA
- HPLC section: look for ≥99% purity and a clean chromatogram (one dominant peak).
- MS section: look for a statement that observed mass matches theoretical mass, ideally with the values shown.
- Methods: the COA should name the techniques and the lab that ran them.
Third-party vs. in-house
The same two tests can be run in-house or by an independent, accredited lab. Third-party results carry more weight because the lab has no commercial incentive to inflate a number. The strongest standard is a batch-specific COA from an independent lab reporting both HPLC and MS.
Key takeaways
- HPLC = purity; MS = identity.
- A complete COA reports both, tied to your batch.
- Independent testing is more credible than in-house-only figures.
FAQ
Can a peptide be 99% pure but the wrong molecule? Yes. That’s exactly why MS identity confirmation is essential alongside HPLC purity.
What is a “shoulder” on a chromatogram? A small bump beside the main peak, indicating a closely related impurity. Cleaner peaks with no shoulders are better.
Do all suppliers run mass spec? Not all do, or they may run it only occasionally. Prefer suppliers that provide MS identity on a per-batch basis.
Browse verified research peptides
Every batch we ship is independently tested by Janoshik Analytical — HPLC for purity, mass spectrometry for identity — with a batch-matched Certificate of Analysis you can verify yourself. Browse the catalog → · See the latest COAs →
*For laboratory and research use only. Not for human or veterinary use, consumption, or administration. Nothing in this article is medical advice or a claim that any compound treats, cures, or prevents any condition.*