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Techniques and Methods 10–C20

Automated Determination of the Stable Carbon Isotopic Composition (δ13C) of Total Dissolved Inorganic Carbon (DIC) and Total Nonpurgeable Dissolved Organic Carbon (DOC) in Aqueous Samples: RSIL Lab Codes 1851 and 1852

By Kinga M. Révész and Daniel H. Doctor

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The purposes of the Reston Stable Isotope Laboratory (RSIL) lab codes 1851 and 1852 are to determine the total carbon mass and the ratio of the stable isotopes of carbon (δ13C) for total dissolved inorganic carbon (DIC, lab code 1851) and total nonpurgeable dissolved organic carbon (DOC, lab code 1852) in aqueous samples. The analysis procedure is automated according to a method that utilizes a total carbon analyzer as a peripheral sample preparation device for analysis of carbon dioxide (CO2) gas by a continuous-flow isotope ratio mass spectrometer (CF-IRMS). The carbon analyzer produces CO2 and determines the carbon mass in parts per million (ppm) of DIC and DOC in each sample separately, and the CF-IRMS determines the carbon isotope ratio of the produced CO2. This configuration provides a fully automated analysis of total carbon mass and δ13C with no operator intervention, additional sample preparation, or other manual analysis. To determine the DIC, the carbon analyzer transfers a specified sample volume to a heated (70 °C) reaction vessel with a preprogrammed volume of 10% phosphoric acid (H3PO4), which allows the carbonate and bicarbonate species in the sample to dissociate to CO2. The CO2 from the reacted sample is subsequently purged with a flow of helium gas that sweeps the CO2 through an infrared CO2 detector and quantifies the CO2. The CO2 is then carried through a high-temperature (650 °C) scrubber reactor, a series of water traps, and ultimately to the inlet of the mass spectrometer. For the analysis of total dissolved organic carbon, the carbon analyzer performs a second step on the sample in the heated reaction vessel during which a preprogrammed volume of sodium persulfate (Na2S2O8) is added, and the hydroxyl radicals oxidize the organics to CO2. Samples containing 2 ppm to 30,000 ppm of carbon are analyzed. The precision of the carbon isotope analysis is within 0.3 per mill for DIC, and within 0.5 per mill for DOC.

First posted April 28, 2014

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:

Révész, K.M., and Doctor, D.H., 2014, Automated determination of the stable carbon isotopic composition (δ13C) of total dissolved inorganic carbon (DIC) and total nonpurgeable dissolved organic carbon (DOC) in aqueous samples: RSIL lab codes 1851 and 1852: U.S. Geological Survey Techniques and Methods, book 10, chap. C20, 38 p.,

ISSN 2328-7055 (online)



Summary of Procedures

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

Appendix A. Step-by-Step Procedure to Collect Water Samples for Determination of the δ13C of Dissolved Inorganic Carbon (DIC) Within the Samples (RSIL Lab Code 1851)

Appendix B. Step-by-Step Procedure to Collect Water Samples for Determination of the δ13C of Dissolved Organic Carbon (DOC) Within the Samples (RSIL Lab Code 1852)

Appendix C. Step-by-Step Procedure to Log Samples Into LIMS-LSI

Appendix D. Step-by-Step Procedure to Print a Template

Appendix E. Step-by-Step Procedure to Add Sample Information to ISODAT and DIC-DOC—Sequence Table

Appendix F. Recommended Settings, Checklist Before Each Run, and ”Start Run” Procedure

Appendix G. Step-by-Step Procedure to Retrieve Data from ISODAT and Apply a Blank Correction and Mass-Dependent Correction

Appendix H. Step-by-Step Procedure to Determine and Apply Isotopic Correction Factors and Evaluate Data in LIMS-LSI

Appendix I. Step-by-Step Procedure to Report Data

Appendix J. Troubleshooting

Appendix K. Step-by-Step Procedure for Changing the Reaction Furnace as Needed

Appendix L. Step-by-Step Procedure to Make Reference Standards

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