Carbon isotope mass-transfer measurement

Proton transfer reactions to and from carbon have also provided data to test theories of kinetic isotope effects. The large difference in mass between hydrogen and deuterium means that large kinetic effects are observed with these isotopes and proton transfer to and from carbon is therefore a suitable reaction for measuring these effects. 

With the development of liquid scintillation counters which permit tracer levels of tritium to be measured accurately, isotope exchange reactions are now usually carried out with tritium rather than deuterium. Frequently, however, it is useful to compare rates of exchange for all three isotopes and deuterium exchange may be followed using, for example, mass spectrometry [22]. An example of the application of isotope exchange to proton transfer from carbon is shown in eqns. (8) and (9) for the hydroxide ion catalysed exchange of phenylacetylene in aqueous solution [23], viz. 

As shown in Fig. 2, in CSIA, organic compounds are separated with gas chromatography and on-line fed to a combustion imit where they are totally converted to simple gases such as CO2 or H2 (for isotope analysis of carbon and hydrogen, respectively). The combustion gases are transferred to an isotope-ratio mass spectrometer (IRMS) that measures precisely the isotopic composition of these gases. For example, in the case of carbon, the element by far most frequently determined today, the ratio of masses 44 ( C02) and 45 ( C02) is measured. 

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