Mass spectrometry

An Isotope Ratio Mass Spectrometer (IRMS) separates atoms with different mass. At Centre for Ice and Climate, mass spectrometers are used for analysis of the isotopic composition of the ice and of the gas in the bubbles of the glacier ice.

The isotope ratio mass spectrometer uses the fact that heavier isotopes are harder to deflect than light isotopes. The IRMS includes three fundamental parts, (1) a "source" of positively charged ions or molecular ions, (2) a magnet, and (3) ion collectors/detectors.

  1. The source is a low-pressure chamber into which the introduced sample or standard gas is ionized by an electron beam produced by a hot filament. After formation, the ions are accelerated and focused by charged plates into a beam that enters a vacuum flight tube.
  2. The fast moving ions pass through a magnetic field that curves their trajectories. The trajectories with highest mass/charge ratio are curved less than those with lower mass/charge ratio, and the ion beam is there separated into distinct beams.
  3. The intensities of these beams are then measured by collectors. The measurements yield the abundances of ions with different mass/charge ratios.
Mass spectrometer

Schematic depicting of a triple-collector IRMS system to analyze the isotopic composition of CO2. The same principle is used for analysis of the isotopes of 16O, just with a different set-up of the collectors.

Read more about laser absorption isotope measurements at Centre for Ice and Climate or read more about mass spectrometry at Wikipedia (opens in a new window)