Mass spectrometry identity testing, explained

A purity figure tells you how much of the vial is peptide. It doesn't tell you which peptide. That second question — identity — is answered by mass spectrometry (MS), and a complete Certificate of Analysis includes both.

What mass spec measures

Every molecule has a characteristic mass. Mass spectrometry works by converting the sample into charged particles and measuring their mass-to-charge ratio very precisely. For a peptide, the measured mass is compared against the expected molecular weight calculated from its amino-acid sequence. If they match, the material is confirmed to be the molecule named on the label. If they don't, something is wrong — it's a different compound, a modified one, or a mislabelled vial.

That's why a certificate will show identity as "confirmed" against the theoretical mass. For example, a peptide with an expected molecular weight of 1419.5 g/mol should return a matching mass on MS.

Why purity without identity isn't enough

Consider a sample that comes back at 99% pure by HPLC. That sounds reassuring — but purity only says the material is homogeneous, not that it's correct. A vial could contain 99% of the wrong peptide. Only mass-spec identity closes that gap. This is the reasoning behind pairing the two tests: HPLC proves it's clean, MS proves it's the right molecule. More on why both matter here.

How to check it yourself

On a Certificate of Analysis, look for an identity or mass-spectrometry line confirming the molecular weight for the stated compound, tied to the same lot code as the purity result. If a supplier can show purity but not identity, you only have half the picture. You can look up any DNR lot's certificate — each one carries both HPLC purity and mass-spec identity for that exact batch.

The takeaway

Mass spectrometry is the identity half of quality verification: it confirms the vial contains the molecule it claims to. Combined with an HPLC purity figure — and tied to a specific lot — it's what turns a purity claim into verifiable evidence. Every DNR Peptides lot ships with both. See the range →