Methods and Facilities

• Finnigan Delta Plus continuous flow isotope ratio mass spectrometer, capable of analyzing carbon dioxide, gaseous nitrogen, gaseous oxygen, sulfur dioxide, and methyl chloride. Peripherals include a Carlo Erba elemental analyzer for analysis of carbon-, nitrogen-, and sulfur-bearing materials and a TC/EA introduction system for analysis of oxygen-, nitrogen-, and hydrogen-bearing substances.
  
  
• Two Thermo-Finnigan Delta XP continuous flow isotope ratio mass spectrometers, capable of analyzing gaseous hydrogen, carbon dioxide, nitrogen, oxygen, and/or other gases.
  
  
• Finnigan MAT 251 dual inlet mass spectrometer, capable of analyzing carbon dioxide, gaseous nitrogen, nitrous dioxide, and gaseous hydrogen for stable isotopic composition (used mainly for gaseous nitrogen). Modified by adding sample and standard mercury pistons for improved accuracy at low abundances.
  
  
• DuPont 21-491 double-focusing mass spectrometer with electric sector with dual inlet and double collector. Capable of analyzing carbon dioxide, gaseous nitrogen, gaseous oxygen, nitrous dioxide, etc. Used primarily for carbon dioxide from water and carbonate sample preparation. Peripherals include an automated 20-port manifold and a 48-port VG Micromass oxygen-18 water equilibration system.
  
  
• VG Micromass 602 dual inlet hydrogen mass spectrometer. Peripherals include an automated 60-port air-bath manifold for gaseous hydrogen-water equilibration.
  
  
• Vacuum lines: carbonate/water extraction line, "Craig-type" carbon dioxide-methane line, reference gas-standard preparation line with 400 split capacity, and other miscellaneous preparation lines with Toepler pumps, GCs, etc.

Capabilities:

• Hydrogen-2 of water: Sample preparation by equilibration with gaseous hydrogen and automated analysis; requires 10 microliters to 2 milliliters of water; precision is around ±1 ‰. Water is extracted from soils and plants by distillation with toluene; recommended sample size is 1-5 ml water. Water from fluid inclusions (~5 uL) is extracted using the crushed-tube technique and converted to gaseous hydrogen using U.
  
  
• Oxygen-18 of water: Sample preparation by equilibration with carbon dioxide and automated analysis; sample size is 0.1 to 2.0 milliliters; precision is around ± 0.1 ‰. Water is extracted from soils and plants by distillation with toluene; recommended sample size is 1-5 ml water per analysis.
  
  
• 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. Continuous flow isotope ratio analysis with preparation using Finnigan Automated Gasbench inlet system; preferred sample size is 0.2 micromoles of carbon; precision approximately ±0.1 ‰ for carbon and oxygen.
  
  
• 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 umoles of carbon; precision is approximately ± 0.1 ‰. Continuous flow isotope ratio analysis with preparation using Finnigan Automated Gasbench inlet system; preferred sample size is 0.2 micromoles of carbon; precision approximately ±0.1 ‰.
  
  
• Hydrogen-2 and carbon-13 of methane: Dual inlet isotope ratio analysis of atmospheric, dissolved, and soil methane with preparation by concentration, GC purification, combustion (conversion of water to gaseous hydrogen by uranium); sample size >15 micromoles of methane; precision is approximately ±2 ‰ for hydrogen and ±0.2 ‰ for carbon. Under preparation is the continuous flow isotope ratio analysis with sample preparation by Finnigan GCC inlet system.
  
  
• 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. 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 removed 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; precision is around ±0.2 ‰.
  
  
• 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; precision is around ±0.2 ‰.
  
  
• 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; precision is around ±0.2 ‰.
  
  
• 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.
  
  
• 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.
  
  
• Oxygen-18 in nitrate: Dual inlet isotope ratio analysis with sample preparation by freeze-drying, ion exchange, and combustion with catalyzed graphite to form gaseous carbon dioxide; requires around 20 to 100 micromoles of nitrate; precision is approximately ± 0.3 ‰ for oxygen. 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 ‰.
  
  
• 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 removed 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 ‰.
  
  
• 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 gasous oxygen; precision is approximately ±0.2 ‰.
  
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