Delta Plus IRMS

The Center has 2 stable isotope IRMS systems available to do ion ratio measurements for C, N2, H2 and O2 containing compounds for both solid (dried powder/granular) and liquid (aqueous) samples.  IRMS is a technique where the mass spectrometer measures the ratios of the stable isotopes NOT abundances.

Isotopes are elemental family members that differ by their number of neutrons in their nucleus, but have the same protons.  For example, for carbon there is the stable carbon 12, carbon 13 and the radioactive carbon 14; all three have 6 protons.  But the atomic number differences are determined by extra neutrons (1, 2 or 3 in this case).  Chemically, the carbon isotopes behave similarly but their physical characteristics can be significantly different.  Certain processes like evaporation (for example H2O), digestion and photosynthesis, will prefer either the heavier or lighter isotope.  The IRMS mass spectrometer can measure these subtle process differences.

The IRMS has several inlet systems that introduce the sample (either solid, liquid or gas; depending on technique) into the mass spectrometer for measurement.  An elemental analyzer is configured to combust dried granular samples to release and separate nitrogen gas from carbon dioxide gas to measure ratios of carbon and nitrogen stable isotope ratios of organic compounds.

The Center also has a Gasbench II device that does headspace gas sample introduction into the mass spectrometer.  These headspace gas samples can be generated from solid granular carbonates or carbonates dissolved into water for carbon and oxygen stable isotopes and hydrogen and oxygen from aqueous materials.  Sensitivity is dependent on the compound and matrix and amounts of sample have to be adjusted to fall within the linear range of the mass spectrometer detectors.