Dataset Information

H₂ clumped isotope measurements at natural isotopic abundances.

ABSTRACT:

Rationale

Molecular hydrogen (H₂ ) is an important gas for atmospheric chemistry, and an indirect greenhouse gas due to its reaction with OH. The isotopic composition of H₂ (δD) has been used to investigate its atmospheric budget; here we add a new observable, the clumped isotopic signature ΔDD, to the tools that can be used to study the global cycle of H₂ .

Methods

A method for determining ΔDD in H₂ was developed using the high-resolution MAT 253-Ultra isotope ratio mass spectrometer (Thermo Fisher). The HH, HD and DD abundances are quantified at medium resolution (M/ΔM ≈ 6000), which is sufficient for HD⁺ and DD⁺ to be distinguished from H₃ ⁺ and H₂ D⁺ , respectively. The method involves sequential measurement of isotopologues, and DD is measured using an ion counter. For verification, catalytic ΔDD equilibration experiments were performed at temperatures of up to 850°C.

Results

The typical precision obtained for ΔDD is 2-6‰, close to the theoretical counting statistics limit, and adequate for detecting the expected natural variations. Compatibility and medium-term reproducibility are consistent with the precision values. The method was validated using temperature equilibration experiments, which showed a dependence of ΔDD on temperature as expected form theoretical calculations.

Conclusions

We have established a method for determining ΔDD in H₂ at natural isotopic abundances, with a precision that is adequate for observing the expected variations in atmospheric and other natural H₂ . This method opens the road to new research on the natural H₂ cycle.

SUBMITTER: Popa ME

PROVIDER: S-EPMC6590658 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

H<sub>2</sub> clumped isotope measurements at natural isotopic abundances.

Popa Maria Elena ME Paul Dipayan D Janssen Christof C Röckmann Thomas T

Rapid communications in mass spectrometry : RCM 20190201 3

<h4>Rationale</h4>Molecular hydrogen (H<sub>2</sub> ) is an important gas for atmospheric chemistry, and an indirect greenhouse gas due to its reaction with OH. The isotopic composition of H<sub>2</sub> (δD) has been used to investigate its atmospheric budget; here we add a new observable, the clumped isotopic signature ΔDD, to the tools that can be used to study the global cycle of H<sub>2</sub> .<h4>Methods</h4>A method for determining ΔDD in H<sub>2</sub> was developed using the high-resoluti ...[more]

PMID: 30378194

Similar Datasets

Project description:RationaleOxygen isotope exchange between O2 and CO2 in the presence of heated platinum (Pt) is an established technique for determining the δ17 O value of CO2 . However, there is not yet a consensus on the associated fractionation factors at the steady state.MethodsWe determined experimentally the steady-state α17 and α18 fractionation factors for Pt-catalyzed CO2 -O2 oxygen isotope exchange at temperatures ranging from 500 to 1200°C. For comparison, the theoretical α18 equilibrium exchange values reported by Richet et al. (1997) have been updated using the direct sum method for CO2 and the corresponding α17 values were determined. Finally, we examined whether the steady-state fractionation factors depend on the isotopic composition of the reactants, by using CO2 and O2 differing in δ18 O value from -66 ‰ to +4 ‰.ResultsThe experimentally determined steady-state fractionation factors α17 and α18 are lower than those obtained from the updated theoretical calculations (of CO2 -O2 isotope exchange under equilibrium conditions) by 0.0024 ± 0.0001 and 0.0048 ± 0.0002, respectively. The offset is not due to scale incompatibilities between isotope measurements of O2 and CO2 nor to the neglect of non-Born-Oppenheimer effects in the calculations. There is a crossover temperature at which enrichment in the minor isotopes switches from CO2 to O2 . The direct sum evaluation yields a θ value of ~0.54, i.e. higher than the canonical range maximum for a mass-dependent fractionation process.ConclusionsUpdated theoretical values of α18 for equilibrium isotope exchange are lower than those derived from previous work by Richet et al. (1997). The direct sum evaluation for CO2 yields θ values higher than the canonical range maximum for mass-dependent fractionation processes. This demonstrates the need to include anharmonic effects in the calculation and definition of mass-dependent fractionation processes for poly-atomic molecules. The discrepancy between the theory and the experimental α17 and α18 values may be due to thermal diffusion associated with the temperature gradient in the reactor.

Project description:RationaleClumped isotope geochemistry examines the pairing or clumping of heavy isotopes in molecules and provides information about the thermodynamic and kinetic controls on their formation. The first clumped isotope measurements of carbonate minerals were first published 15 years ago, and since then, interlaboratory offsets have been observed, and laboratory and community practices for measurement, data analysis, and instrumentation have evolved. Here we briefly review historical and recent developments for measurements, share Tripati Lab practices for four different instrument configurations, test a recently published proposal for carbonate-based standardization on multiple instruments using multi-year data sets, and report values for 21 different carbonate standards that allow for recalculations of previously published data sets.MethodsWe examine data from 4628 standard measurements on Thermo MAT 253 and Nu Perspective IS mass spectrometers, using a common acid bath (90°C) and small-sample (70°C) individual reaction vessels. Each configuration was investigated by treating some standards as anchors (working standards) and the remainder as unknowns (consistency standards).ResultsWe show that different acid digestion systems and mass spectrometer models yield indistinguishable results when instrument drift is well characterized. For linearity correction, mixed gas-and-carbonate standardization or carbonate-only standardization yields similar results. No difference is observed in the use of three or eight working standards for the construction of transfer functions.ConclusionsWe show that all configurations yield similar results if instrument drift is robustly characterized and validate a recent proposal for carbonate-based standardization using large multiyear data sets. Δ47 values are reported for 21 carbonate standards on both the absolute reference frame (ARF; also refered to as the Carbon Dioxide Equilibrated Scale or CDES) and the new InterCarb-Carbon Dioxide Equilibrium Scale (I-CDES) reference frame, facilitating intercomparison of data from a diversity of labs and instrument configurations and restandardization of a broad range of sample sets between 2006, when the first carbonate measurements were published, and the present.

Dataset Information

H₂ clumped isotope measurements at natural isotopic abundances.

Rationale

Methods

Results

Conclusions

Publications

H<sub>2</sub> clumped isotope measurements at natural isotopic abundances.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

Dataset Information

H2 clumped isotope measurements at natural isotopic abundances.

Rationale

Methods

Results

Conclusions

Publications

H<sub>2</sub> clumped isotope measurements at natural isotopic abundances.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets

H₂ clumped isotope measurements at natural isotopic abundances.