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Methods & SOPs

Capabilities and Standards of Procedures:

The analytical methods given below include some that are offered by the Reston Stable Isotope Laboratory. For a list of prices for these services, please see our Services and Prices page.

  • δ2H replicate analysis of water by dual-inlet isotope-ratio mass spectrometry: Sample preparation by equilibration with gaseous hydrogen and automated analysis; requires 1 to 2 milliliters of water. Isotopic analysis by laser absorption spectrometry is avoided as a primary analytical technique for all USGS water samples because this method can produce anomalous results that will not hold up in court. The "gold standard" for δ2H determination on water is dual-inlet isotope-ratio mass spectrometry. For 2-mL samples, the estimated expanded uncertainty of replicate hydrogen-isotope measurements is 2 per mil. 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.
    pdf of SOP: Révész, Kinga, and Coplen, T.B., 2008, Determination of the δ(2H/1H) of water: RSIL lab code 1574, chap. C1 of Révész, Kinga, and Coplen, T.B., eds., Methods of the Reston Stable Isotope Laboratory: U.S. Geological Survey Techniques and Methods 10–C1, 27 p.
  • δ18O replicate analysis of water by dual-inlet isotope-ratio mass spectrometry: Sample preparation by equilibration with carbon dioxide and automated analysis; requires 0.2 to 2.0 milliliters of water. Isotopic analysis by laser absorption spectrometry is avoided as a primary analytical technique for all USGS water samples because this method can produce anomalous results that will not hold up in court. The "gold standard" for δ18O determination on water is dual-inlet isotope-ratio mass spectrometry. For 2-mL samples, the estimated expanded uncertainty of replicate oxygen-isotope measurements is 0.2 per mil. 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.
    pdf of SOP: Révész, Kinga, and Coplen, T.B., 2008, Determination of the δ(18O/16O) of water: RSIL lab code 489, chap. C2 of Révész, Kinga, and Coplen, Tyler B., eds., Methods of the Reston Stable Isotope Laboratory: U.S. Geological Survey Techniques and Methods, 10–C2, 28 p.
  • δ2H and δ18O replicate analysis of water extracted from soils and plants: Water is extracted from soils and plants by distillation with toluene; recommended sample size is that which will provide 1 to 5 milliliters of water per sample. Analysis is by dual-inlet isotope-ratio mass spectrometry. Isotopic analysis by laser absorption spectrometry is deprecated because the smallest remaining fraction of toluene in water will produce anomalous isotopic results.
    pdf of SOP: Révész, Kinga, Buck, Bryan, and Coplen, T.B., 2012, Determination of the δ2H and δ18O of soil water and water in plant matter; RSIL lab code 1700, chap. 19 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, 21 p., available only at http://pubs.usgs.gov/tm/10c19/.
  • δ15N and δ18O replicate analysis of dissolved nitrate in water: Dissolved nitrate in water is converted to nitrous oxide (N2O) by denitrifying bacteria, and the nitrous oxide is analyzed for nitrogen and oxygen isotopic abundance by continuous-flow isotope-ratio mass spectrometry. A minimum total amount of 0.002 milligrams of nitrate as nitrogen is required. The estimated expanded uncertainty of δ15N measurement results for samples with nitrate concentrations of at least 0.06 mg/L as nitrogen is ±0.5 per mil unless otherwise specified, and this value is conservative. The estimated expanded uncertainty of δ18O measurement results for samples with nitrate concentrations of at least 0.06 mg/L as nitrogen is ±0.5 per mil unless otherwise specified, and this value is conservative. If any given sample were resubmitted for nitrogen- and oxygen-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Coplen, T.B., Qi, Haiping, Révész, Kinga, Casciotti, Karen, and Hannon, J.E., 2012, Determination of the δ15N and δ18O of nitrate in water; RSIL lab code 2900, chap. 17 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.0 released in 2006): U.S. Geological Survey Techniques and Methods, book 10, 35 p., available only at http://pubs.usgs.gov/tm/2006/tm10c17/. (Supersedes version 1.0 released in 2007.)
  • δ15N replicate analysis of dissolved nitrate in water: Dissolved nitrate in water is converted to nitrous oxide (N2O) by denitrifying bacteria, and the nitrous oxide is analyzed for nitrogen isotopic abundance by continuous-flow isotope-ratio mass spectrometry. A minimum total amount of 0.002 milligrams of nitrate as nitrogen is required. The estimated expanded uncertainty of δ15N measurement results for samples with nitrate concentrations of at least 0.06 mg/L as nitrogen is ±0.5 per mil unless otherwise specified, and this value is conservative. If any given sample were resubmitted for nitrogen-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Coplen, T.B., Qi, Haiping, Révész, Kinga, Casciotti, Karen, and Hannon, J.E., 2012, Determination of the δ15N of nitrate in water; RSIL lab code 2899, chap. 16 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.0 released in 2006): U.S. Geological Survey Techniques and Methods, book 10, 35 p., available only at http://pubs.usgs.gov/tm/2006/tm10c16/. (Supersedes version 1.0 released in 2007.)
  • δ15N replicate analysis of dissolved ammonium in water: Dissolved ammonium in freshwater or saline water is converted to gaseous ammonia (NH3), converted quantitatively to ammonium sulfate, and combusted in an elemental analyzer to gaseous nitrogen and sulfur dioxide. The gaseous nitrogen is separated by gas chromatography and analyzed for nitrogen isotopic composition with continuous-flow isotope-ratio mass spectrometry. The concentration of ammonium in sample must be at least 0.2 milligrams per kilogram as nitrogen. A minimum amount of ammonium in sample must be 0.2 milligrams as nitrogen. The estimated expanded uncertainty of δ15N measurement results is ±0.8 per mil unless otherwise specified. If any given sample were resubmitted for nitrogen-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Hannon, Janet E., and Böhlke, John Karl, 2008, Determination of the δ(15N/14N) of ammonium (NH4+) in water: RSIL lab code 2898, chap. C15 of Révész, Kinga, and Coplen, Tyler B., eds., Methods of the Reston Stable Isotope Laboratory: U.S. Geological Survey, Techniques and Methods, 10–C15, 30 p.
  • δ13C of dissolved inorganic carbon: Dissolved carbon that has been precipitated in the field with ammoniacal strontium chloride solution. In the laboratory, the strontium carbonate solution is reacted with phosphoric acid to liberate carbon dioxide, which is analyzed for carbon isotopic abundance by dual-inlet isotope-ratio mass spectrometery. An amount of sample that yields 50 milligrams of strontium carbonate is required. The expanded uncertainty is ±0.2 per mil, unless otherwise indicated. 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.
    pdf of SOP: 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 http://pubs.usgs.gov/tm/10c18/.
  • δ34S replicate analysis of dissolved sulfate in water: Dissolved sulfate is precipitated to barium sulfate, combusted in an elemental analyzer to sulfur dioxide, and analyzed for sulfur isotopic composition with continuous-flow isotope-ratio mass spectrometry. The concentration of sulfate must be at least 20 milligrams per liter. The estimated expanded uncertainty of δ34S measurement results is ±0.4 per mil unless otherwise specified. If any given sample were resubmitted for sulfur-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Révész, Kinga, Qi, Haiping, and Coplen, T.B., 2012, Determination of the δ34S of sulfate in water; RSIL lab code 1951, chap. 10 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.1 released in 2007): U.S. Geological Survey Techniques and Methods, book 10, 33 p., available only at http://pubs.usgs.gov/tm/2006/tm10c10/. (Supersedes versions 1.0 and 1.1 released in 2006 and 2007, respectively.)
  • δ34S replicate analysis of low-concentration sulfate in water: Dissolved sulfate having a concentration of less than 20 milligrams per liter is collected on an anion-exchange resin in the field, eluted in the laboratory with potassium chloride, precipitated with barium chloride to barium sulfate, combusted in an elemental analyzer to sulfur dioxide, and analyzed for sulfur isotopic composition with continuous-flow isotope-ratio mass spectrometry. The estimated expanded uncertainty of δ34S measurement results is ±0.4 per mil unless otherwise specified. If any given sample were resubmitted for sulfur-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Révész, Kinga, Qi, Haiping, and Coplen, T.B., 2012, Determination of the δ34S of low-concentration sulfate in water; RSIL lab code 1949, chap. 8 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.1 released in 2007): U.S. Geological Survey Techniques and Methods, book 10, 35 p., available only at http://pubs.usgs.gov/tm/2006/tm10c8/. (Supersedes versions 1.0 and 1.1 released in 2006 and 2007, respectively.)
  • δ34S replicate analysis of total sulfur in solids: A homogeneous powder is combusted with an elemental analyzer. Combusted gases are separated by gas chromatography and the sulfur dioxide is analyzed for sulfur isotopic abundance by continuous-flow isotope-ratio mass spectrometry. The estimated expanded uncertainty of δ34S measurement results is ±0.4 per mil unless otherwise specified. If any given sample were resubmitted for sulfur-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Révész, Kinga, Qi, Haiping, and Coplen, T.B., 2012, Determination of the δ34S of total sulfur in solids; RSIL lab code 1800, chap. 4 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.1 released in 2007): U.S. Geological Survey Techniques and Methods, book 10, 31 p., available only at http://pubs.usgs.gov/tm/2006/tm10c4/. (Supersedes versions 1.0 and 1.1 released in 2006 and 2007, respectively.)
  • δ15N and δ13C replicate analysis of total nitrogen and carbon in solids: A homogeneous powder is combusted to gaseous nitrogen and carbon dioxide with an elemental analyzer. These gases are separated by gas chromatography and are analyzed for nitrogen and carbon isotopic abundance by continuous-flow isotope-ratio mass spectrometry. A minimum required amount of nitrogen and carbon in a sample is 0.15 milligrams and 0.15 milligrams. The estimated expanded uncertainty of δ15N measurement results is ±0.5 per mil unless otherwise specified. The estimated expanded uncertainty of δ13C measurement results is ±0.5 per mil unless otherwise specified. If any given sample were resubmitted for nitrogen- and carbon-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Révész, Kinga, Qi, Haiping, and Coplen, T.B., 2012, Determination of the δ15N and δ13C of total nitrogen and carbon in solids; RSIL lab code 1832, chap. 5 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.1 released in 2007): U.S. Geological Survey Techniques and Methods, book 10, 31 p., available only online at http://pubs.usgs.gov/tm/2006/tm10c5/. (Supersedes versions 1.0 and 1.1 released in 2006 and 2007, respectively.)
  • δ15N replicate analysis of total nitrogen in solids: A homogeneous powder is combusted to gaseous nitrogen and carbon dioxide with an elemental analyzer. These gases are separated by gas chromatography and the gaseous nitrogen is analyzed for nitrogen isotopic abundance by continuous-flow isotope-ratio mass spectrometry. A minimum required amount of nitrogen in a sample is 0.15 milligrams. The estimated expanded uncertainty of δ15N measurement results is ±0.5 per mil unless otherwise specified. If any given sample were resubmitted for nitrogen-isotope analysis, the measured values would fall within the uncertainty bounds of the previous results more than 95 percent of the time.
    pdf of SOP: Révész, Kinga, Qi, Haiping, and Coplen, T.B., 2012, Determination of the δ15N of total nitrogen in solids; RSIL lab code 2893, chap. 11 of Stable isotope-ratio methods, sec. C of Révész, Kinga, and Coplen, T.B. eds., Methods of the Reston Stable Isotope Laboratory (slightly revised from version 1.1 released in 2007): U.S. Geological Survey Techniques and Methods, book 10, 30 p., available only online at http://pubs.usgs.gov/tm/2006/tm10c11/. (Supersedes versions 1.0 and 1.1 released in 2006 and 2007, respectively.)

 

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