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Instrument Description

The gas mass spectrometer combines the features of gas-liquid chromatography and mass spectrometry to categorize different substances. It identifies trace elements in materials previously thought to have disintegrated beyond identification. A spectral plot displays the mass of each fragment. The mass spectrum is then used for qualitative identification and to piece together the mass of the original molecule.

The gas mass spectrometer is a sensitive, high-resolution gas analysis mass spectrometer under full software control. The instrument design and the materials used in its construction allow the precise measurement of low molar mass gases. In particular, the isotopic composition of hydrogen can be precisely determined, by measuring the relative abundances of the three naturally occurring isotopes 1H, sometimes denoted protium, 2H (deuterium), and 3H (tritium).  

Since hydrogen is such a ubiquitous element and is present in most polymer materials, the inner surfaces of the mass spectrometer in contact with the vacuum are constructed (wherever possible) from alloy materials. This includes the vacuum side of any seals, valves, and gauges, with Viton and other polymers used only when essential. 



The Finnigan MAT 271 is a sector field gas mass spectrometer having a mass range of 1-350 atomic mass units (AMU) and is used to quantitatively analyze gases using an electron ionization process to produce ions that can be measured to a high precision. The MAT 271 gas mass spectrometer will be used to provide isotopic and total elemental composition of He, CO2, O2, H2, N2 and the fission gases Kr and Xe in support of various post-irradiated examination (PIE) and other infrastructure programs at INL.


  • The resolution of the system is user-definable, beyond 5,000, through computer-controlled variable slits.

    • This allows 2H and 1H2 peaks to be resolved at mass 2.

    • Resolve resolution of CO2 and N2O peaks at mass 44.

  • Minor components in gas mixtures, down to 10 ppm, can be monitored, since the wide dynamic range of the dual detector system delivers acquisitions of over 10 orders of magnitude.

  • Mass range of 1-350 atomic mass units (AMU).