Glossary
Mass spectrometry
An analytical technique that measures the mass-to-charge ratio of ionised molecules to confirm a compound's identity by its molecular weight.
Mass spectrometry ionises a sample and measures the mass-to-charge ratio of the resulting ions, yielding a molecular weight for the compound. For peptides, the common formats are electrospray ionisation (ESI-MS) and MALDI-TOF. A match between the observed and expected molecular weight confirms that the material is the intended peptide — that is, it verifies identity. Crucially, a mass-spec match says nothing about purity or quantity: a sample can be correctly identified yet still contain impurities or less peptide than the label implies, which is why mass spectrometry is read alongside HPLC and amino acid analysis rather than on its own.
Covered in depth in Peptide laboratory testing methods.
Related terms
- MALDI-TOF
- Matrix-assisted laser desorption/ionisation time-of-flight, a mass-spectrometry technique used to confirm a peptide's molecular weight.
- Molecular weight
- The mass of one molecule of a compound, expressed in daltons (Da) — the value mass spectrometry checks against the expected figure.
- HPLC
- High-performance liquid chromatography — the standard technique for separating a mixture and measuring chromatographic purity.
- Sequence
- The specific order of amino acids in a peptide, which defines its identity and its theoretical molecular weight.