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Techniques and Methods 10–C18

Determination of the δ13C of Dissolved Inorganic Carbon in Water; RSIL Lab Code 1710

By Glenda L. Singleton, Kinga Révész, and Tyler B. Coplen

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The purpose of the Reston Stable Isotope Laboratory (RSIL) lab code 1710 is to present a method to determine the δ13C of dissolved inorganic carbon (DIC) of water. The DIC of water is precipitated using ammoniacal strontium chloride (SrCl2) solution to form strontium carbonate (SrCO3). The δ13C is analyzed by reacting SrCO3 with 100-percent phosphoric acid (H3PO4) to liberate carbon quantitatively as carbon dioxide (CO2), which is collected, purified by vacuum sublimation, and analyzed by dual inlet isotope-ratio mass spectrometry (DI-IRMS). The DI-IRMS is a DuPont double-focusing mass spectrometer. One ion beam passes through a slit in a forward collector and is collected in the rear collector. The other measurable ion beams are collected in the front collector. By changing the ion-accelerating voltage under computer control, the instrument is capable of measuring mass/charge (m/z) 45 or 46 in the rear collector and m/z 44 and 46 or 44 and 45, respectively, in the front collector. The ion beams from these m/z values are as follows: m/z 44 = CO2 = 12C16O16O, m/z 45 = CO2 = 13C16O16O primarily, and m/z 46 = CO2 = 12C16O18O primarily. The data acquisition and control software calculates δ13C values.

First posted April 11, 2012

For additional information contact:
Director, Reston Stable Isotope Laboratory
U.S. Geological Survey
12201 Sunrise Valley Drive, MS 431
Reston, VA 20192

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Suggested citation:

Singleton, G.L., Révész, Kinga, and Coplen, T.B., 2012, Determination of the δ13C of dissolved inorganic carbon in water; RSIL lab code 1710, chap. 18 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory: U.S. Geological Survey Techniques and Methods, book 10, 28 p., available only at



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Summary of Procedure

Reporting Units and Operational Range

Reference Materials and Documentation

Labware, Instrumentation, and Reagents

Sample Collection, Preparation, Analysis, Retention Times, and Disposal

Data Acquisition, Processing, Evaluation, Quality Control, and Quality Assurance

Health, Safety, and Waste-Disposal Information

References Cited


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