Isotopes of Hydrogen and Oxygen of Freshwater

Requirements

  • Samples can be submitted in 30 mL wide-mouth HDPE bottles (Fisher Scientific Cat # 02-893-5A) or any plastic bottle of your choice – Avoid tin foil lined caps.
  • Samples must be filtered using 0.45 μm luer lock syringe filters (Fisher Scientific Cat # 50-109-8711).
  • Bottles must be submitted with as little headspace as possible, ideally with no headspace.
  • Samples do not need to be refrigerated, although, for long term storage, this is recommended.
  • Samples should be sent as soon as possible to our facility, where they will be refrigerated upon arrival.

Methodology – 2 Options

1. TCEA – δ18O and δ2H Preparation

Water samples and standards are pipetted individually into 2 mL vials sealed with Teflon silicone screw cap septa (Cole-Parmer Cat # SK-98701-90). A series of ten samples are bracketed by standards before and after analysis. Analysis always begins with a set of ten deionized water conditioners to monitor drift, then a set of standards.

Secondary standards include a broad spectrum of depleted and enriched aliquots, from ice core melt water to bottled water from France and Italy. These standards are kept frozen until the day before use, where they are completely thawed at room temperature, then shaken. Secondary standards were calibrated by primary standards of VSMOW2, SLAP2, and GISP obtained from the IAEA, Vienna. Two quality control standards (one internally calibrated, and a medium natural isotope water from EA Consumables # B2193) are also included at various intervals throughout the run.

Sample analysis is performed via automated injections using a CTC Analytics PAL autosampler into a Thermo Finnigan Thermal Conversion Elemental Analyzer (TCEA) set at 1400 °C and linked via continuous flow to a Thermo Fisher Delta V Isotope Ratio Mass Spectrometer. The autosampler syringe is rinsed twice with HPLC grade methanol, then subjected to a vacuum for five seconds to remove residual methanol. The syringe is then rinsed three times with the sample before injecting 0.5 μL into the TCEA reactor. This is repeated three times for each sample and standard. The sample is combusted to produce elemental hydrogen. Glassy carbon in the reactor produces carbon monoxide as the oxygen phase. These two analytes are carried by a continuous helium stream set at 100 mL/min and separated by a 1.5 m long stainless steel GC column before being admitted to the IRMS for isotope analysis of δ2H and δ18O. Of the three injections performed for each sample and standard, only the third is used for calibration purposes. Memory effect is monitored by calculating the standard deviation of all three peaks.

A set of four secondary water standards are analyzed every ten samples, at the beginning of a run, and at the end. Raw δ2H and δ18O values are plotted versus their known isotopic values to produce a four-point calibration curve. Sample data is calibrated to this curve and reported to the VSMOW scale. Typical linear regression is 0.9996 or better for both the hydrogen and oxygen calibration curves.

Two quality control standards are analyzed after every ten samples and calibrated to the VSMOW scale. Compiled results of EA Consumables Medium Natural Isotopic Water # B2193 and a Greenland Ice Core water show that sample data can be reported as better than ±0.4‰ for δ2H, and better than ±0.16‰ for δ18O.

Turnaround Time:

    • ≤ 60 samples: 3-4 weeks to process.
    • > 60 samples: 6-8 weeks to process.

2a. GasBench – δ18O Preparation

0.5 mL of water sample and standards are pipetted individually into 12 mL Labco exetainer vials (Cat # 938W) and capped. Vials are flushed for five minutes at 100-150 mL/min with a 0.5% carbon dioxide in ultra-high purity helium mixture. Freshwaters are left to equilibrate a minimum of 18 hours, and saline waters for five days at 30 °C, prior to analysis.

A series of ten samples are bracketed by standards before and after analysis. Standards include a broad spectrum of depleted and enriched aliquots, from ice core melt water to bottled water from France and Italy. These standards are kept frozen until the day before use, where they are completely thawed at room temperature, then shaken. Secondary standards were calibrated by primary standards of VSMOW2, SLAP2, and GISP obtained from the IAEA, Vienna. Two quality control standards (one internally calibrated, and a medium natural isotope water from EA Consumables # B2193) are also included at various intervals throughout the run.

The analysis is performed using a needle syringe injected via a CTC Analytics Combi-Pal autosampler with ultra-high purity helium acting as a carrier gas. Sample CO2 gas is passed through a Poraplot Q GC column (25 m x 0.32 mm ID, 32 °C, 2.0 mL/min) located inside a Thermo Fisher GasBench II front-end peripheral, then onto a Thermo Fisher Delta V Advantage isotope ratio mass spectrometer for analysis of δ18O. Sample and standard chromatography include eight CO2 samples peaks in the results. However, the first and last sample peaks are dropped from the calibration, and the remaining six are averaged. δ18O data is corrected by generating a four-point calibration curve of the previously mentioned standards, and raw sample data is corrected to the VSMOW scale. Precision for δ18O is ±0.08‰.

2b. GasBench – δ2H Preparation

0.5 mL of water sample and standards are pipetted individually into 12 mL Labco exetainer vials (Cat # 938W). ***Note*** The sample aliquot used for analysis of δ18O can be used for the preparation of δ2H analysis. Activated charcoal (Fisher Scientific Cat # AC403995000), copper wire (EA Consumables Cat # B1016), and a platinum catalyst rod are added to each vial and capped. These are added to remove dissolved organic carbon and sulfur compounds that can interfere with the analysis. Vials are flushed for five minutes at 100-150 mL/min with a 2% hydrogen in ultra-high purity helium mixture. Freshwaters are left to equilibrate a minimum of 40 minutes, and saline waters for 24 hours at 30 ºC, prior to analysis.

A series of ten samples are bracketed by standards before and after analysis. Standards include a broad spectrum of depleted and enriched aliquots, from ice core melt water to bottled water from France and Italy. These standards are kept frozen until the day before use, where they are completely thawed at room temperature, then shaken. Secondary standards were calibrated by primary standards of VSMOW2, SLAP2, and GISP obtained from the IAEA, Vienna. Two quality control standards (one internally calibrated, and a medium natural isotope water from EA Consumables # B2193) are also included at various intervals throughout the run.

The analysis is performed using a needle syringe injected via a CTC Analytics Combi-Pal autosampler with ultra-high purity helium acting as a carrier gas. Sample H2 gas is passed through a Poraplot Q GC column (25 m x 0.32 mm ID, 32 °C, 2.0 mL/min) located inside a Thermo Fisher GasBench II front-end peripheral, then onto a Thermo Fisher Delta V Advantage isotope ratio mass spectrometer for analysis of δ2H. Sample and standard chromatography include eight hydrogen sample peaks in the results. However, the first and last sample peaks are dropped from the calibration, and the remaining six are averaged. δ2H data is corrected by generating a four-point calibration curve of the previously mentioned standards, and raw sample data is corrected to the VSMOW scale. Precision for δ2H is ±0.4‰.

Turnaround Time:

    • ≤ 30 samples: 3-4 weeks to process.
    • > 30 samples: 6-8 weeks to process.