What is mass spectrometry?

The three core stages

A mass spectrometer works in three stages. First, an ion source converts neutral molecules into charged ions, for example by electron ionisation or by electrospray for fragile biomolecules. Second, a mass analyser — such as a quadrupole, time-of-flight, or orbitrap — separates ions according to their mass-to-charge ratio using electric or magnetic fields. Third, a detector records how many ions arrive at each m/z value. The whole path is held under high vacuum so that ions travel without colliding with air molecules.

Reading a mass spectrum

The output is a mass spectrum: a series of peaks whose positions give the m/z of each ion and whose heights give relative abundance. The heaviest peak often corresponds to the intact molecular ion, revealing the molecular mass.

Larger molecules can be fragmented deliberately, and the pattern of fragment masses acts as a structural fingerprint. Tandem mass spectrometry (MS/MS) selects one ion, breaks it apart, and analyses the pieces — a powerful route to sequencing peptides and identifying unknowns.

Uses in research

Mass spectrometry is central to proteomics, metabolomics, environmental analysis, and forensic chemistry. Coupled to gas chromatography (GC-MS) or to liquid chromatography (LC-MS), it both separates and identifies the components of complex mixtures. Its high sensitivity lets researchers detect trace substances, while accurate-mass instruments help confirm molecular formulae. Reliable results depend on calibration against reference standards and on reporting acquisition parameters so that analyses can be reproduced.