Mass Spectrometry

Once we know the amount of helium and carbon we can analyse the gases for the ratio of their isotopes. In particular, we want to know the ratio of ³He to ⁴He and ¹³C to ¹²C. Mass spectrometers are analytical instruments that can measure isotope ratios. A new rare gas mass spectrometer (MAP215E) was installed in the Fluid & Volatiles Laboratory in early 2000.

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In the picture, we see a rare gas mass spectrometer (in the background — with its green magnet) interfaced to the inlet line (foreground) which purifies the gas prior to analysis. The glass vials are connected to the inlet section allowing the volatiles to be expanded into the line where the active gases (N2, O2, CO) are removed by sorption onto hot titanium metal. Freezing at different temperatures allows us to separate the rare gases so that finally we isolate pure helium. This helium is expanded into the mass spectrometer for isotopic analysis.

Carbon dioxide is also analysed for its isotopic composition on a mass spectrometer (different in type to the one shown here) — in this case, in the laboratory of SIO professor, Martin Wahlen.