17O correction

The ion current on the mass 45 Faraday cup is comprised of 13C16O2+ as well as 12C17O16O+. The latter isobaric interference amounts to about 7% of the total ion current. If the oxygen isotopic signature between the sample and the reference gas is different, the 17O contribution to the m/z 45 ion current can be corrected for by measuring the δ18O signature on m/z 46 and assume a constant law for the fractionation of 17O and 18O. Although this does not strictly apply, this is the standard procedure first used by Harmon Craig in 1957. It is usually referred to as 'Craig' correction. A number of improvements or alterations have been proposed in the literature including the set of absolute ratios for the reference materials and the exponent of the fractionation law. We have compiled the different correction techniques and algorithms in an XLS file (17O_corrections.xls) which is available for downloading. The corrections can be tested using different inputs for δ13C and δ18O in the input fields. In 2010, we published a linearized 17O correction, based on the Assonov correction. The new linearized approach shares its simplicity with the Craig correction but takes the isotopic relations in the world oxygen pools into account.


Further reading:

Brand, W. A.; Assonov, S.A.; Coplen, T. B.
Correction for the 17O interference in δ(13C) determinations when analyzing CO2 with stable isotope mass spectrometry (IUPAC Technical Report)
Pure Applied Chemistry 82 (8), 1719–1733 (2010)
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