Technique for High-Precision Analysis of Triple Oxygen Isotope Ratios in Carbon Dioxide

Abstract

Since the discovery of mass-independent isotope effects in stratospheric and tropospheric gases, the analysis of triple oxygen isotope abundance in carbon dioxide gained in importance. However, precise triple oxygen isotope determination in carbon dioxide is a challenging task due to mass-interference of (17)O and (13)C variations. Here, we present a novel analytical technique that allows us to determine slight deviations of CO(2) from the terrestrial fractionation line [TFL]. Our approach is based on isotopic equilibration between CO(2) gas and CeO(2) powder at 685 degrees C and subsequent mass spectrometric analysis of ceria powder by infrared-laser fluorination. We found that beta(CO2-CeO2), the exponent in the relation alpha(17/16) = (alpha(18/16))(beta), amounts to 0.5240 +/- 0.0011 at 685 degrees C. The oxygen isotope anomaly of CO(2) (Delta(17)O) can be determined for a single analysis of CeO(2) with a precision of +/-0.05 per thousand (1sigma). Our CO(2)-CeO(2) equilibration procedure is performed with an excess of CO(2) so that one analysis of Delta(17)O on CO(2) requires at least 3.5 mmol of CO(2) gas. Our new technique allows accurate and precise determination of Delta(17)O in CO(2) and opens up a new field for investigating triple oxygen isotope abundance in various types of natural CO(2).

On the triple oxygen isotope composition of carbon dioxide from some combustion processes

“…An excess of CO 2 was equilibrated with CeO 2 powder at 685°C. It was shown by Assonov and Brenninkmeijer (2001) and confirmed by Hofmann and Pack (2010) and Hofmann et al (2012a) that CO 2 and CeO 2 fully exchange at these conditions. The equilibrated CeO 2 was analyzed for its triple oxygen isotope ratios by infrared-laser fluorination coupled with continuous flow gas chromatograph isotope ratio monitoring mass spectrometry (CFGCirmMS).…”

“…The D 17 O value of the CO 2 was measured with the CO 2 -CeO 2 equilibration method (Hofmann and Pack, 2010;Hofmann et al, 2012a). An excess of CO 2 was equilibrated with CeO 2 powder at 685°C.…”

Equilibrium mass-dependent fractionation relationships for triple oxygen isotopes

“…Boaz Luz's group has set examples on how this ratio can be determined precisely by experiments (e.g., Luz et al, 1999;Angert et al, 2003;Luz, 2005, 2007;Luz and Barkan, 2005;Landais et al, 2006). Hofmann and Pack (2010) have also determined this ratio for CO 2 -CeO 2 system experimentally.…”

Continuous-flow IRMS technique for determining the <sup>17</sup>O excess of CO<sub>2</sub> using complete oxygen isotope exchange with cerium oxide

“…Although the standard deviation of a single run is higher than for already established methods that use CeO 2 (Assonov and Brenninkmeijer, 2001;Hofmann and Pack, 2010;Mahata et al, 2012) it can be decreased statistically with injecting multiple aliquots of the same sample.…”

“…Our method is the first fully automated analytical system that uses CeO 2 as the isotope exchange medium. The 3 h labour characterized for a single measurement in the offline techniques (Assonov and Brenninkmeijer, 2001;Hofmann and Pack, 2010;Mahata et al, 2012) was decreased to a minimum: connecting air samples to the injection lines, filling the LN 2 dewar and running the measurement sequence by press- ing the start button. That was possible by constructing the automated sample injection, by applying ISODAT 3.0 software and electronic devices to control movement of valves, LN 2 trap and gas flow in the MFCs, and finally by using a microdosing LN 2 pump to keep the liquid nitrogen level in the CO 2 trap constant.…”