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RSIL Home > Isotope Fractionation Project > Methods and SOPs

Methods & SOPs

Capabilities and Standards of Procedures:

The analytical methods given below include some that are offered for service to the USGS user community and many others that are being developed for research purposes within the Reston Stable Isotope Fractionation Project. For a list of prices for the services that are offered by the Isotope Fractionation Project, please see our Services and Prices page.

  • Hydrogen-2 of water: Sample preparation by equilibration with gaseous hydrogen and automated analysis; requires 10 microliters to 2.0 milliliters of water. For 2-mL samples, the 2-sigma uncertainties of hydrogen isotopic measurement results are 2 ‰. This means that if the same sample were resubmitted for isotopic analysis, the newly measured value would lie within the uncertainty bounds 95 percent of the time. Water is extracted from soils and plants by distillation with toluene; recommended sample size is 1-5 ml water. Click here for a pdf of SOP.
  • Oxygen-18 of water: Sample preparation by equilibration with carbon dioxide and automated analysis; sample size is 0.1 to 2.0 milliliters of water. For 2-mL samples, the 2-sigma uncertainties of oxygen isotopic measurement results are 0.2 ‰. This means that if the same sample were resubmitted for isotopic analysis, the newly measured value would lie within the uncertainty bounds 95 percent of the time. Water is extracted from soils and plants by distillation with toluene; recommended sample size is 1-5 ml water per analysis. Click here for a pdf of SOP.
  • Carbon-13 /oxygen-18 of carbonates: Automated dual inlet isotope ratio analysis with sample preparation of carbon dioxide by acidification, purification; preferred sample size is > 25 micromoles of carbon; precision is approximately ± 0.05 ‰ and ± 0.1 ‰ for carbon and oxygen, respectively. This on-line pdf of SOP is under preparation, please contact Kinga Révész at krevesz@usgs.gov with questions.
  • Carbon-13 of DIC: Automated dual inlet isotope ratio analysis with sample preparation by precipitation with ammoniacal strontium chloride solution, filtration, purification, acidified of strontium carbonate; sample size is > 25 micromoles of carbon; one-sigma uncertainty is approximately ± 0.1 ‰. Click here for a pdf of SOP. Please contact Kinga Révész at krevesz@usgs.gov with questions.
  • Carbon-13 in Solids: Click here for an on-line pdf of SOP
  • Hydrogen-2 and carbon-13 of methane: Continuous flow isotope ratio analysis with sample preparation by Finnigan GCC inlet system. This on-line pdf of SOP is under preparation, please contact Kinga Révész at krevesz@usgs.gov with questions.
  • Sulfur-34 of dissolved sulfate: Sulfate from samples with concentrations < 20 mg/L are collected using anion exchange resin, being careful to strip out any dissolved sulfide by acidifying and bubbling nitrogen gas before dissolved sulfate is collected. Sulfate is eluted from the resin using KCl. Click here for a pdf of SOP.

    Sulfate samples above 20 mg/L can be collected directly in sample bottles after any necessary stripping of sulfide. Sulfate is precipitated as barium sulfate, treated with hydrogen peroxide or Br-water to remove organic material. Continuous flow isotope ratio analysis with sample preparation of barium sulfate by conversion to sulfur dioxide with an elemental analyzer; sample size > 300 micrograms barium sulfate. The 2-sigma uncertainty of sulfur isotopic results is 0.4 ‰. This means that if the same sample were resubmitted for isotopic analysis, the newly measured value would lie within the uncertainty bounds 95 percent of the time. Click here for a pdf of SOP.
  • Sulfur-34 of dissolved sulfide: The water sample is collected in a large carboy, acidified, and bubbled with nitrogen. The hydrogen sulfide released is collected in a silver nitrate trap. Continuous flow isotope ratio analysis with sample preparation of silver sulfide by conversion to sulfur dioxide with an elemental analyzer; sample size > 300 micrograms silver sulfide. The 2-sigma uncertainty of sulfur isotopic results is 0.4 ‰.  This means that if the same sample were resubmitted for isotopic analysis, the newly measured value would lie within the uncertainty bounds 95 percent of the time.
  • Sulfur-34 of solid sulfide: Sulfur is extracted with HCl or chromium dichloride/HCl. Bubbling nitrogen carries hydrogen sulfide to a silver nitrate trap. Continuous flow isotope ratio analysis with sample preparation of silver sulfide by conversion to sulfur dioxide with an elemental analyzer; sample size > 300 micrograms silver sulfide; uncertainty is around ± 0.2 ‰. Click here for a pdf of SOP.
  • Nitrogen-15 in solids, liquids, and gases (e.g., dissolved ammonium, nitrate, organic nitrogen, nitrous oxide, nitrogen, soil, solid organic matter, rocks, mixed gases, etc.): Sample preparation by various combinations of freeze-drying, distillation, vacuum extraction, ion exchange and combustion to isolate compounds and produce pure gaseous nitrogen for mass spectrometry. Dual inlet isotope ratio analysis requires approximately 1 to 10 micromoles of gaseous nitrogen; precision is approximately ± 0.1 ‰. Continuous flow isotope ratio analysis with conversion of nitrate, nitrite, organic nitrogen, soil nitrogen to gaseous nitrogen with an elemental analyzer; sample size > 0.2 micromoles nitrogen; precision is approximately ± 0.15 ‰. Continuous flow nitrogen-15 and oxygen-18 isotopic analysis of dissolved nitrate (plus nitrite) by bacterial denitrification to nitrous oxide and subsequent isotopic analysis; total amount of nitrate in sample must be at least 0.002 mg as N. The 2-sigma uncertainty of oxygen isotopic results of nitrates is 1.0 ‰ unless otherwise indicated.
    pdf of SOP: Determination of the δ15N and δ13C of Total N and C in Solids: RSIL Lab Code 1832, by Kinga Révész, Haiping Qi, and Tyler B. Coplen, 2012.
    pdf of SOP: Determination of the δ15N of Total Nitrogen in Solids: RSIL Lab Code 2893, by Kinga Révész, Haiping Qi, and Tyler B. Coplen, 2012.
    pdf of SOP: Determination of the δ15N of Nitrate in Solids: RSIL Lab Code 2894, by Tyler B. Coplen, Haiping Qi, Kinga Révész, Karen Casciotti, and Janet Hannon, 2012.
    pdf of SOP: Determination of the δ15N and δ18O of Nitrate in Solids: RSIL Lab Code 2897, by Tyler B. Coplen, Haiping Qi, Kinga Révész, Karen Casciotti, and Janet Hannon, 2012.
    on-line pdf of SOP: Determination of the δ(15N/14N) of Ammonium in Water: RSIL Lab Code 2898, by Janet Hannon and J.K. Bohlke, 2009.
    pdf of SOP: Determination of the δ15N of Nitrate in Water: RSIL Lab Code 2899, by Tyler B. Coplen, Haiping Qi, Kinga Révész, Karen Casciotti, and Janet Hannon, 2012.
    pdf of SOP: Determination of the δ15N and δ18O of Nitrate in Water: RSIL Lab Code 2900, by Tyler B. Coplen, Haiping Qi, Kinga Révész, Karen Casciotti, and Janet Hannon, 2012.
  • Nitrogen-15 /oxygen-18 in nitrous oxide: Samples prepared by GC, cryofocused for continuous-flow analysis; requires around 10-20 nanomoles of nitrous dioxide; precision around ± 0.2 ‰ for nitrogen and ± 0.4 ‰ for oxygen. This on-line pdf of SOP is under preparation, please contact Kinga Révész at krevesz@usgs.gov with questions.
  • Oxygen-18 in nitrate: Continuous flow isotope ratio analysis with sample preparation by freeze-drying, ion exchange, and conversion to carbon monoxide with thermal combustion/elemental analyzer system; precision is approximately ± 0.4 ‰. This on-line pdf of SOP is under preparation, please contact Kinga Révész at krevesz@usgs.gov with questions.
  • Oxygen-18 of dissolved sulfate: Sulfate from samples with concentrations < 20 mg/L are collected using anion exchange resin, being careful to strip out any dissolved sulfide by acidifying and bubbling nitrogen gas before dissolved sulfate is collected. Sulfate is eluted from the resin using KCl. Sulfate samples above 20 mg/L can be collected directly in sample bottles after any necessary stripping of sulfide. Sulfate is precipitated as barium sulfate, treated with hydrogen peroxide or Br-water to remove organic material. Continuous flow isotope ratio analysis with sample preparation of barium sulfate by conversion to carbon monoxide with thermal combustion/elemental analyzer system; precision is approximately ± 0.3 ‰. This on-line pdf of SOP is under preparation, please contact Kinga Révész at krevesz@usgs.gov with questions.
  • Oxygen-18 in oxygen gas: Dual inlet isotope ratio analysis with sample preparation by vacuum extraction, GC separation, and conversion to carbon dioxide; requires around 10 to 20 micromoles; precision is approximately ± 0.2 ‰. Continuous flow isotope ratio analysis with gaseous oxygen separation by headspace creation by vacuum, extraction with a Tekmar sampler, and GC separation with a Finnigan GPI system; sample amount is in the range of 1 micromole gaseous oxygen; precision is approximately ± 0.2 ‰. This on-line pdf of SOP is under preparation, please contact Kinga Révész at krevesz@usgs.gov with questions.

 

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