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. 2020 Jul 16;5(29):17926-17930.
doi: 10.1021/acsomega.0c00839. eCollection 2020 Jul 28.

Enhanced Stability of Stable Isotopic Gases

Richard Socki  1 , Matt Matthew  2 , James McHale  2 , Jun Sonobe  3 , Megumi Isaji  3 , Tracey Jacksier  1
Affiliations

Enhanced Stability of Stable Isotopic Gases

Richard Socki et al. ACS Omega. .

Abstract

Pure gases and mixtures containing stable isotopes are used in a wide variety of applications including health care, food authentication, geochemistry, and environmental monitoring. It is therefore important to understand the role of moisture, which is one of the most critical impurities in compressed gas mixtures and pure gases, in their stability. Gaseous carbon dioxide (CO2) was used as a proxy for the evaluation of the effects of its isotopic composition, when in contact with moisture throughout the depletion of a cylinder's contents, as well as pressure regulation and long-term stability. To accentuate the detrimental effects of moisture on CO2 isotopic stability, enriched 18O-water was added to natural-abundance, gaseous carbon dioxide. The δ18O-CO2 changed from -23.16‰ vs Vienna Pee Dee Belemnite (VPDB) to +109‰ vs VPDB. It was further demonstrated that with appropriate cylinder preparation to reduce residual moisture, source material purity with low moisture content, and pressure regulation (from 57.0 down to 0.5 bar), both δ13C and δ18O remained consistent within ±0.04 and ±0.06‰, respectively, throughout the entire cylinder contents. Pressure reduction using a dual-stage regulator yielded statistically consistent results at the 99% confidence level from delivered pressures of 0.1-0.8 bar. Furthermore, the isotopic values remained consistent during a 1 year shelf-life study, illustrating the ability to utilize and regulate pressurized gases as working reference standard gases.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Experimental configuration to study the effect of pressure regulation vs a background that was obtained by sequential gas expansion (without the use of a regulator). Stepwise pressure reduction/expansion: Sequential expansion through Segments a, b, and c. The volume of the system is approximately 3024 mL. Effect of pressure reduction: Segments a and d with an in-line pressure regulator. The volume of the aliquoter in Segment d is 5 mL.
Figure 2
Figure 2
δ13C(VPDB) and δ18O(VPDB) vs CO2 cylinder pressure in bar of a gas-phase CO2 cylinder, where 35 bar represents a full cylinder. The flow rate of CO2 throughout the duration of the experiment (∼5 weeks) was kept constant at ∼50 mL/min.
Figure 3
Figure 3
Stability of gaseous δ13C–CO2 (VPDB) and δ18O–CO2 (VPDB) over 1 year.
Figure 4
Figure 4
Experimental configuration to evaluate the dependence of δ13C–CO2 (VPDB) and δ18O–CO2 (VPDB) on cylinder pressure.
See this image and copyright information in PMC

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