Mass Spectrometer for Isotope Ratio Analysis

Isobaric interferences from other isotope species at the target masses require the measurement of more masses than just the targeted isotope ratio for a necessary correction. For the measurement of 8 C, three collectors at m/z 44,45 and 

46 are necessary (see Table 2.49). Algorithms for a fully automated correction of isobaric ion contributions are implemented in modern isotope ratio MS data systems, for example, for the isobaric interferences of and on m/z46 of CO2, see Table 2.50 (Craig, 1957). Other possible interferences such as CO on Nj, N2O on CO2 can be taken care of by the interface technology. 

Standardization in isotope ratio monitoring measurements should be done exclusively using the principle of Identical Treatment of reference and sample material , the IT Principle . Mostly, isotopic referencing is made with a co-injected peak of standard gas. 

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