Isotope-ratio mass spectrometry

Isotope-ratio mass spectrometry measures the relative abundances of isotopes in a sample by separating ions according to their mass-to-charge ratios and comparing their signals.

Magnetic-sector mass spectrometer: A mass spectrometer that separates ions by deflecting them through a magnetic field according to momentum and charge. Many isotope-ratio instruments use magnetic-sector analyzers to resolve neighboring isotopes.
Stable isotope analysis: The study of variations in naturally occurring stable isotope abundances to investigate materials and processes. It is the broad analytical practice that relies heavily on isotope-ratio measurements.
Isotope: An atom of a chemical element with a particular number of neutrons and therefore a particular atomic mass. The instrument compares isotopes, which share an element's proton number but differ in neutron number.
Quadrupole mass spectrometer: A mass spectrometer that filters ions using oscillating electric fields between four rods. It is widely used for mass analysis but often offers less precision for isotope ratios than dedicated instruments.
Electron ionization: An ionization method in which energetic electrons remove electrons from gaseous atoms or molecules. It converts sample gases into ions that the analyzer can separate by isotope mass.
Radiocarbon dating: A method for estimating the age of once-living material from its carbon-14 content. Isotope measurements quantify carbon-14 relative to stable carbon isotopes in dating samples.
Mass-to-charge ratio: The quotient of an ion's mass and electric charge, commonly used to distinguish ions in mass spectrometry. The analyzer separates ions by this quantity rather than by isotope identity alone.
Multi-collector inductively coupled plasma mass spectrometry: A mass-spectrometric technique that ionizes samples in a plasma and measures multiple ion beams simultaneously. It extends high-precision isotope-ratio analysis to many elements, especially in solution samples.
Faraday cup: An ion detector that measures electrical current produced when ions strike a conductive collector. Separate collectors can measure isotope beams simultaneously as electrical currents.
Stable isotope probing: A method that tracks labeled stable isotopes into biomolecules to identify active organisms or pathways. Isotope-ratio measurements reveal which organisms incorporated an isotopically labeled substrate.

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