Year: 2025
Type: article
Abstract: ABSTRACT Rationale The reaction of carbonate materials with phosphoric acid is a standard method for extracting CO 2 , not only for the subsequent analysis of the ratios of 13 C/ 12 C and 18 O/ 16 O but also for the ratios of 13 C 18 O 16 O/ 12 C 16 O 16 O and 12 C 18 O 18 O/ 12 C 16 O 16 O and the calculation of the Δ 47 and Δ 48 values. For the determination of Δ 47 and Δ 48 values, possible exchange between the CO 2 and H 2 O in the acid is of particular importance as this influences the precision and accuracy of the measurement. Methods Stochastic and non‐stochastic CO 2 was exposed to “fresh” and “used” phosphoric acid at 90°C. Fresh acid is defined as acid that had not previously reacted with calcium carbonate, whereas “used” acid had previously dissolved a significant amount of carbonate material. The δ 13 C, δ 18 O, Δ 47 , and Δ 48 values of the CO 2 were then measured using a Thermo‐253 plus using conventional methods, and the rate and the amount of exchange were determined. Results When exposed to “fresh” phosphoric acid, 13 C 18 O 16 O and 12 C 18 O 18 O readily exchanged with the H 2 O in the acid, attaining Δ 47 and Δ 48 values close to those expected as a result of equilibration with H 2 O at 90°C. In contrast with “used” acid, the rate of exchange of 13 C 18 O 16 O with H 2 O in the acid was negligible, whereas the exchange of 12 C 18 O 18 O, although reduced compared with “fresh” acid, was still significant. Conclusions Such data have implications on the precision and accuracy of Δ 47 and Δ 48 values in systems in which the acid has been previously used to react in multiple samples, as well as in those in which fresh acid is used for every sample. The use of a sacrificial amount of carbonate prior to the reaction of “real” samples will reduce some of the changes observed in this study.
DOI: 10.1002/rcm.10159
Authors: Peter K. Swart, Chaojin Lu
Language: English
Subfield: Geochemistry and Petrology
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: hybrid
Estimated APC paid: $4,840
Funder: University of Miami
OpenAlex ID: W4415518234