How Peptide Purity Is Tested (HPLC & Mass Spectrometry)

When a supplier claims "99% purity," that figure comes — or should come — from two analytical techniques run on the actual batch: HPLC for purity and mass spectrometry for identity. Understanding what each measures tells you how much a Certificate of Analysis is really worth.

HPLC: measuring purity

High-Performance Liquid Chromatography separates the components of a sample. The peptide solution is pushed through a column packed with a fine material; different molecules travel through at different speeds and emerge (elute) at different times. A detector records each component as a peak on a graph called a chromatogram.

The target peptide appears as one dominant peak. Impurities — truncated sequences, deletion products, residual reagents — appear as smaller peaks. Purity is calculated as the area of the target peak as a percentage of the total area of all peaks:

Purity (%) = (target peak area ÷ total peak area) × 100

A clean chromatogram with a single sharp peak and minimal minor peaks indicates high purity. This is why the chromatogram itself — not just the number — is the meaningful evidence. A supplier who publishes purity but not the trace is asking you to take the figure on faith.

Mass spectrometry: confirming identity

Purity tells you the material is pure, but pure what? Mass spectrometry answers that. It ionises the peptide and measures its mass-to-charge ratio, yielding the molecular weight with high precision.

Every peptide sequence has a theoretical molecular weight calculated from its amino acids. If the measured mass matches the theoretical mass, the identity is confirmed — you have the peptide you ordered, not a similar-looking substitute. A mismatch is a red flag no purity figure can rescue.

Why an independent lab matters

A manufacturer testing its own product has an obvious incentive problem. An independent, third-party laboratory has none — its result stands on its own reputation. This is why credible COAs name an external lab, and why we run every batch through an independent laboratory and publish the certificate, with batch numbers you can verify yourself, before the product is listed.

Putting it together

A trustworthy batch has:

1. An HPLC chromatogram showing a dominant, clean peak (purity)
2. A mass-spec result matching the peptide's theoretical weight (identity)
3. A batch number tying both to the specific vial in your hand
4. An independent laboratory named and dated

Anything less, and "99% purity" is just a number on a page. For more on reading the certificate itself, see How to Read a COA.

All products are supplied strictly for laboratory research use only. Not for human or animal consumption.