Gas Source Mass Spectrometry
Gas source mass spectrometry (GS-MS) is the name given to instrumentation used for the determination of stable isotopic compositions of those particular elements that can be analyzed in a gaseous form. It differs from thermal ionization mass spectrometry (q.ν.) where the elements of interest are admitted to the instrument in a solid form. GS-MS is principally employed for the analysis of hydrogen (as H2), carbon (as CO2), nitrogen (as N2), oxygen (as CO2, or O2) and sulfur (as SO2, or SF6). GS-MS is also used for the analysis of chlorine (as CH3Cl) and silicon (as SiF4), but these applications are comparatively rare. A further suite of elements, the noble gases (He, Ne, Ar, Kr and Xe), are also analyzed using a form of GS-MS, but this is a highly specialized variety and will not concern us here (the interested reader is referred instead to 40Ar/39Ar dating).
In a geologic context the species that can be determined using-GS-MS often have a certain commonality