Mass spectrometry

Mass spectrometry measures the mass of a sample's molecules, and on a peptide certificate it is the test that confirms the main compound has the molecular weight of the peptide on the label.

A mass spectrometer ionizes molecules and sorts them by their mass-to-charge ratio. For peptides it is usually coupled to liquid chromatography as LC-MS: the chromatography separates the sample, and the spectrometer weighs what comes off the column. If the main peak's measured mass matches the sequence's calculated molecular weight, the compound is very likely the one claimed.

This is what HPLC alone cannot do. HPLC reports how much of the sample is one substance; mass spectrometry reports what that substance weighs. A certificate that shows purity without a mass or reference-standard identity test leaves open whether the dominant compound is the right one.

Mass confirmation has limits of its own. Two peptides with the same composition in a different order have the same mass, and so do mirror-image forms of a residue, so a mass match does not rule out every substitution. Read the method line of a certificate to see whether identity was tested at all, and by which method.

Related terms

• High-performance liquid chromatography
• Reference standard

UPDATED OCTOBER 26, 2026 · REVIEWED BY DEL POTTER, PHD