Isotopic analyses based on the mass spectra of carbon dioxide

Abstract

Measurements of carbon and oxygen isotopic abundances are commonly based on the mass spectrum of carbon dioxide, but analysis of that spectrum is not trivial because three isotope ratios (17O/16O, 18O/16O, and 13C/12C) must be determined from only two readily observable ion-current ratios (45/44 and 46/44). Here, approaches to the problem are reassessed in the light of new information regarding the distribution of oxygen isotopes in natural samples. It is shown that methods of calculation conventionally employed can lead to systematic errors in the computed abundance of 13C and that these errors may be related to incorrect assessment of the absolute abundance of 17O. Further, problems arising during the analysis of samples enriched by admixture of 18O-labeled materials are discussed, and it is shown (i) that serious inaccuracies arise in the computed abundance of 17O and 13C if methods of calculation conventionally employed in the analysis of natural materials are applied to material labeled with 18O but (ii) that computed fractional abundances of 18O are always within 0.4% of the correct result. Methods for exact calculation of two isotope ratios when the third is known are presented and discussed, and a more exact approach to the computation of all three isotope ratios in natural materials is given.

Constraints on the vital effect in coccolithophore and dinoflagellate calcite by oxygen isotopic modification of seawater

“…This study illustrates the potential of an interspecies proxy of the coccoliths to reconstruct palaeo-DIC concentrations and δ 18 O of seawater. Santrock et al, 1985). For the carbon isotopes, the effect of 17 O co-addition is greater and results in a decrease in δ 13 C (-0.03 ‰ in δ 13 C per ‰ of δ 18 O w increase).…”

“…The co-addition of 17 O in the medium also has an effect on the determination of the 45 CO 2 / 44 CO 2 and 46 CO 2 / 44 CO 2 , and hence on δ 13 C DIC and δ 13 C c (Santrock et al, 1985;Brand et al, 2010). As a consequence, without addition of 12 C or 13 C in the spiking solution, we observe a decrease in both δ 13 C DIC and δ 13 C c with increasing δ 18 O w values due to an increase in 17 O concentrations (Fig.…”

Interlaboratory comparison of <i>δ</i><sup>13</sup>C and <i>δ</i>D measurements of atmospheric CH<sub>4</sub> for combined use of data sets from different laboratories

“…Assonov and Brenninkmeijer, 2003). Several algorithms such as Craig (1957) and Santrock et al (1985) have been suggested (see Assonov and Brenninkmeijer, 2003 and references therein) and implemented into software/programmes of the IRMS companies and individual laboratories. Assonov and Brenninkmeier (2003) showed that the bias caused by different 17 O-correction algorithms could exceed general repeatability achieved by IRMS measurements.…”

“…Brackets in the RM column indicate the laboratory from which the original standard scale was propagated. See (1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996) MAT 252 (1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011)(2012)(2013) MAT 253 Allison et al (1995), C2: Santrock et al (1985), C3: Craig (1957), C4: Assonov and Brenninkmeijer (2003). b Raw ion current correction: the Kr interference was corrected by subtracting the Kr-caused anomalies in the raw ion current data.…”

Cometary Isotopic Measurements

“…As the sample elutes from the column it passes through a Rhodium oxide reactor which oxidises the CO to CO 2 . Isotopic exchange on the reactor gives the CO 2 a terrestrial oxygen isotopic signature thus allowing accurate carbon isotopic analysis (Santrock et al 1985). 3.…”