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Correction of mass spectrometric isotope ratio measurements for isobaric isotopologues of O 2 , CO, CO 2 , N 2 O and SO 2
Author(s) -
Kaiser Jan,
Röckmann Thomas
Publication year - 2008
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.3821
Subject(s) - isotopologue , chemistry , isotope , isobaric process , analytical chemistry (journal) , oxygen isotope ratio cycle , stable isotope ratio , ion , mass spectrometry , isotope ratio mass spectrometry , kinetic isotope effect , isotopes of oxygen , deuterium , atomic physics , nuclear physics , molecule , physics , thermodynamics , organic chemistry , chromatography , nuclear chemistry
Gas isotope ratio mass spectrometers usually measure ion current ratios of molecules, not atoms. Often several isotopologues contribute to an ion current at a particular mass‐to‐charge ratio ( m / z ). Therefore, corrections have to be applied to derive the desired isotope ratios. These corrections are usually formulated in terms of isotope ratios ( R ), but this does not reflect the practice of measuring the ion current ratios of the sample relative to those of a reference material. Correspondingly, the relative ion current ratio differences (expressed as δ values) are first converted into isotopologue ratios, then into isotope ratios and finally back into elemental δ values. Here, we present a reformulation of this data reduction procedure entirely in terms of δ values and the ‘absolute’ isotope ratios of the reference material. This also shows that not the absolute isotope ratios of the reference material themselves, but only product and ratio combinations of them, are required for the data reduction. These combinations can be and, for carbon and oxygen have been, measured by conventional isotope ratio mass spectrometers. The frequently implied use of absolute isotope ratios measured by specially calibrated instruments is actually unnecessary. Following related work on CO 2 , we here derive data reduction equations for the species O 2 , CO, N 2 O and SO 2 . We also suggest experiments to measure the required absolute ratio combinations for N 2 O, SO 2 and O 2 . As a prelude, we summarise historic and recent measurements of absolute isotope ratios in international isotope reference materials. Copyright © 2008 John Wiley & Sons, Ltd.