Gas Source: Isotope Ratio
Mass Spectrometry (IRMS)
Gas Source
Isotope Ratio Mass Spectrometry (IRMS) of 1947
In 1947, Alfred Nier developed the first dual-inlet,
double-collector gas-source mass spectrometer. The double
collector allowed the simultaneous measurement of two
isotopes and the dual inlet allowed ratio measurement
on both a sample and a standard by alternating between
inlets. It has since become the measurement technique
of preference for isotope ratios of most of the light
elements (e.g. H, C, N, O and S) because of its relative
simplicity and because the use of international standards
allows comparison of databases from different laboratories. (See
Environmental
Isotopes in Hydrogeology [I. Clark and P. Fritz,
1997] for more information)
In the last
few years, a new methodology to measure d13C
contents of individual compounds in complex organic
mixtures has been developed. This technique, which uses
a capillary column gas chromatograph (GC), a combustion
interface (C) to produce CO2
, that is linked to a modified conventional gas mass-spectrometer
(MS, as described above). This GC-C-MS method has the
capability to measure individual carbon in mixtures
of subnanogram samples with a precision of better than
±0.5%.