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Acid fractionation during carbonate digestion with phosphoric acid – Assessment of two different techniques applied for clumped and stable isotope analysis using a Tuneable Infrared Laser Differential Absorption Spectrometer (TILDAS)
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  • THAMIZHARASAN Sakthivel,
  • Tobias Kluge,
  • Prosenjit Ghosh,
  • Dorothea Stein
THAMIZHARASAN Sakthivel
Indian Institute of Science Centre for Earth Sciences
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Tobias Kluge
Karlsruher Institut fur Technologie Institut fur Angewandte Geowissenschaften
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Prosenjit Ghosh
Indian Institute of Science Centre for Earth Sciences

Corresponding Author:[email protected]

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Dorothea Stein
Karlsruher Institut fur Technologie Institut fur Angewandte Geowissenschaften
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Abstract

Rationale: Aerodyne Tunable Infrared Laser Differential Absorption Spectrometer (TILDAS) allows for the measurement of carbonate-clumped (∆ 638) and stable oxygen isotope ratios (δ 628) without the mass interference of 17O, and understanding acid fractionation factors during phosphoric acid digestion is essential for inter-laboratory data comparison. Here, we present δ 628 and ∆ 638 ratios in CO 2 generated during phosphoric acid digestion of a reference carbonate at different temperatures. Methods: Carrara Marble (MAR-J1) calcite is digested with ⁓104% phosphoric acid using a) Break Seal method is a modified version of a McCrea-type reaction vessel where complete equilibration is achieved between product CO 2 and H 2O generated from the digestion and b) Individual Acid Bath (IAB) where the samples are digested with fresh aliquot of acid each time and the product CO 2 and H 2O simultaneously frozen in a U-trap connected to the reaction chamber by liquid N 2. Results: The regression equations for acid fractionation of δ 628 are: a) Break Seal Method: 1000 ln α (dig. temp- 25℃) = (0.532 ± 0.030) × 10 6/T 2 + (-6.185 ± 0.308) ; R 2 = 0.98. b) IAB: 1000 ln α (dig. temp- 25℃) = (0.359 ± 0.027) × 10 6/T 2 + (-4.114 ± 0.247) ; R 2 = 0.97. The regression equations for acid fractionation of ∆ 638 are: a) Break Seal Method: 1000 ln α (dig. temp - 25℃) = (0.0189 ± 0.0017) × 10 6/T 2 + (-0.2151 ± 0.0174) ; R 2 = 0.95. b) IAB: 1000 ln α (dig. temp - 25℃) = (0.0529 ± 0.0041) × 10 6/T 2 + (-0.6072 ± 0.0356) ; R 2=0.97. Conclusion: The shallow slope of the IAB method for δ 628 and the steeper slope for ∆ 638 indicate minimal resetting of the isotope composition of product CO 2 due to re-equilibration or interaction with free H 2O molecules. This observation enables inter-laboratory comparisons of δ 628 and ∆ 638 in calcite.
21 Oct 2024Submitted to Rapid Communications in Mass Spectrometry
22 Oct 2024Submission Checks Completed
22 Oct 2024Assigned to Editor
22 Oct 2024Review(s) Completed, Editorial Evaluation Pending
26 Oct 2024Reviewer(s) Assigned