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University of California
Stable Isotope Laboratory
Earth and Planetary Sciences
1156 High Street Santa Cruz, CA 95064

Lab: (831) 459-5751
Office: (831) 459-5857
Fax: (831) 459-3074


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Gas Bench Overview

The Gas Bench is a headspace sampling peripheral used to measure:

  • δ18O of natural waters.
  • δD of natural waters.
  • δ13C of dissolved inorganic carbon (DIC) in natural waters.
  • δ15N and δ18O of nitrates and nitrites in natural waters.
  • δ18O and δ13C of calcium carbonate.

  • At UCSC, the Gas Bench is primarily used to measure δ18O and δ13C of DIC in natural waters and δ18O and δ15N of nitrates/nitrites in natural waters.


    Gas Bench Rates


    Continuous Flow: Gas Bench Head Space Autosampler

      Isotope Phase Optimum
    Quantity
    Measurement
    Precision
    Cost per Sample
    Internal* External
    Carbonate Device δ18O Solid 50 µg ± 0.1 ‰ $7.00 $10.78
    δ13C Solid 50 µg ± 0.1 ‰ $7.00 $10.78
    δ15N Liquid 50 µg ± 0.2 ‰ $7.00 $10.78
    δ18O Liquid 50 µg ± 0.3 ‰ $7.00 $10.78
    δD Liquid 500 µl ± 2 ‰ $6.00 $9.24
    δ18O Liquid 500 µl ± 0.4 ‰ $6.00 $9.24
    δ13C Liquid 1000 µl ± 0.1 ‰ $7.00 $10.78
    Sample Types: Calcium Carbonate, Natural waters, Dissolved Inorganic Carbon,
    Dissolved nitrate and/or nitrite of natural waters.
    * An additional 54% University of California overhead (indirect) charge is automatically taken
    from UC based grants when paying for these samples.
    For samples that require sample processing above normal an additional assisted rate of
    $4.50/sample ($6.91/sample external) may be charged.

    Analysis

    δ13C of dissolved inorganic carbon (DIC) in natural waters.

    Carbon isotopic (δ13C) analysis of dissolved inorganic carbon (DIC) in natural waters is done using a Gas Bench II headspace sampling interface coupled to a ThermoFinningan Delta Plus XP isotope ratio mass spectrometer (IRMS). Water samples were injected into helium flushed 12 cc exetainer vials containing 1 ml of 43% phosphoric acid. Over a period of greater than 6 hours, DIC derived CO2 was allowed to evolve from the acidified water into the headspace. After this equilibration period, the headspace gas was entrained into a He stream , passed through two nafion dryers and passed through a PoraPlot Q gas chromatographic (GC) column. The GC column separates CO2 from contaminant N2O gas of the same mass before introduction into the mass spectrometer for isotopic analysis.

    During analysis, calibrated in-house NaHCO3 standards that preceed and are interspersed between samples to correct for linearity (size) effects and drift. A second calibrated laboratory standard is run "as-a-sample" to monitor quality control and long term performance. Standards are prepared daily from NaHCO3 by dissolving bulk powders in water that has been stripped of DIC by sonicatting under a weak vacuum for 1 hour. These laboratory standards, which are selected to be compositionally similar to the samples being analyzed, have been previously calibrated against NIST Standard Reference Materials (NBS-19, NBS-18, and LSVEC).

    Corrected delta values are expressed relative to international standards PDB (PeeDee Belemnite) for δ13C.

    δ18O in natural waters.

    Oxygen isotopic (δ18O) in natural waters is done using a Gas Bench II headspace sampling interface coupled to a ThermoFinningan Delta Plus XP isotope ratio mass spectrometer (IRMS). Sample and standard water are added to a 12 cc exetainer vials and flushed with helium containing 0.3% carbon dioxide. Over a period of greater than 10 hours the water oxygen is allowed to come into isotopic equilibrium with the headspace CO2. After this equilibration period, the headspace gas was entrained into a He stream , passed through two nafion dryers and passed through a PoraPlot Q gas chromatographic (GC) column. The GC column separates CO2 from contaminant N2O gas of the same mass before introduction into the mass spectrometer for isotopic analysis.

    During analysis, calibrated in-house water standards that preceed and are interspersed between samples to correct for source stretching effects and drift. One-to-two calibrated laboratory standard is run "as-a-sample" to monitor quality control and long term performance and make adjustments for source stretching. These laboratory standards, which span most of the δ18O isotopic range found in nature, have been previously calibrated against NIST Standard Reference Materials (SMOW, SLAP, and GISP).

    Corrected delta values are expressed relative to international standards Standard Mean Ocean Water (SMOW) for δ18O.


    Sample Preparation Guidelines