Ionization chamber (ion source)Where the sample is turned into positive ions.
Sample inletWhere the sample, as a gas, enters the machine.
Accelerating platesCharged plates that speed the ions up into a beam.
FilamentA heated wire that gives off electrons.
Electron beamElectrons that knock electrons off the sample to make ions.
RepellerA positive plate that pushes the ions out of the chamber.
Sorting and counting them 4
ElectromagnetIts field bends the path of the ions.
DetectorCounts the ions that arrive, as an electric current.
Ion beamThe stream of ions on its way to the far end.
Vacuum pumpKeeps the inside of the machine empty of air.
How this list was compiled: Every name checked on 2026-09-30 and kept only where at least two of these use it. (1) Wikipedia, Mass spectrometry, https://en.wikipedia.org/wiki/Mass_spectrometry : sample inlet, ion source and ionization chamber, a wire filament heated to give electrons, the electron beam, the repeller electrode, the ion beam, the magnet, the detector, high vacuum. (2) Science Education Resource Center at Carleton College, Gas Source Mass Spectrometry, https://serc.carleton.edu/research_education/geochemsheets/techniques/gassourcemassspec.html : the source, an electron beam from a hot filament, ions sped up and focused into a beam by charged plates, a flight tube bent through an electromagnet, ion collectors, inlet systems. (3) Jim Clark, Chemguide, The mass spectrometer, https://www.chemguide.co.uk/analysis/masspec/howitworks.html : ionisation chamber, ion repeller, the slits the ions are accelerated through, deflection by a magnetic field, ion detector, vacuum pump. Licence: own work
The drawing: Own drawing from plain geometry; nothing traced. Licence: own work
How it works
A mass spectrometer turns a sample into ions, sorts them by mass and counts them. The plan shows the kind with an electromagnet, and follows the sample from the inlet at the left to the detector.
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Making the ions
The sample enters the ionization chamber as a gas. A heated filament sends an electron beam through it, which knocks electrons off and leaves positive ions. The repeller pushes them out, and the accelerating plates speed them into a beam.
Sorting and counting
The electromagnet bends the ion beam. Lighter ions bend more than heavier ones, so only one mass at a time reaches the detector. The vacuum pump keeps air out of the way.
Questions and answers
What are the main parts of a mass spectrometer?
A sample inlet, an ion source, a mass analyzer and a detector, plus a data system. On this plan the ion source is the ionization chamber with its filament and repeller, and the analyzer is the electromagnet.
What does the magnet do in a mass spectrometer?
Its field bends the path of the moving ions. How much an ion bends depends on its mass and its charge: lighter ions are bent more than heavier ions with the same charge.
Why does a mass spectrometer need a vacuum?
So the ions can travel from the chamber to the detector without colliding with air molecules. A vacuum pump keeps the pressure inside very low.
What happens in the ionization chamber?
Electrons from a heated filament cross the chamber and knock electrons off the sample, leaving positive ions. A repeller plate then pushes the ions out toward the accelerating plates.