Carbonate Precipitation Methods for the Measurement of Stable Isotope Ratio of Dissolved Inorganic Carbon
2021
Jeong, Y.J. | Lee, S.J. | Lim, S.S. | Choi, W.J.
The stable carbon (C) isotope ratio (δ¹³C) of dissolve inorganic carbon (DIC) in environmental samples including soil extracts and water samples provides insight into the biogeochemical C cycling. The δ¹³C of DIC can be measured in gas and solid (carbonate precipitates) states, and precipitates measurement of δ¹³C of DIC is more convenient compared to the gases measurement for analyzing a large number of samples. However, it is still uncertain what precipitation conditions, such as pH, headspace, and distilled water, are suitable. To address the question, we conducted a series of precipitation experiments, followed by δ¹³C, under different conditions of pH, headspace, and distilled water as well as precipitating agents (SrCl₂, BaCl₂, and CaCl₂). Our results demonstrated that DIC (depleted in ¹³C) contaminant in double distilled water is the major error factor to decrease the δ¹³C. By combining the results from the experiments, we suggest that reliable δ¹³C data can be obtained by precipitation under the conditions of using DIC-free tertiary distilled water, samples with a high DIC concentration, CaCl₂ addition as a precipitating agent, pH 10.6, and the absence of a headspace produces a reliable δ¹³C measurement.
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