We employ the water fluorination method using Cobalt (III) fluoride to convert H2O into O2 for subsequent triple oxygen isotope analysis on a Thermo MAT253.
We use VSMOW, SLAP, and GISP to calibrate our water flourination system. We have also measured select in-house reference waters for 17Oexcess.
If you would like to submit samples for this analysis, please contact us. See the table below for sample analysis pricing. Given the nature of the Δ17O signal, this analysis requires a minimum of three replicates.
Exhaustive description of analysis
Water is fluorinated to produce O2 as previously described (Barkan and Luz 2005,Baker et al. 2002,Barkan and Luz 2007) and the O2 is collected as in Abe (2008). Briefly, 2 mL of water was injected into a 370 C 15 cm long nickel column containing 7 g CoF3 converting H2O into O2 and creating HF and CoF2 as byproducts. Helium carried O2 at 30 mL min–1 through a trap submerged in liquid nitrogen to collect HF, which was later vented to a fume hood; the NaF trap originally recommended by Baker et al. was not used. The O2 sample was collected in a trap for 20 min, and then transferred to a 14 cm stainless steel cold finger. Both the trap and cold finger contained approximately 40 mg of 5A (4.2 to 4.4 Å) molecular sieve and were submerged in liquid nitrogen. To minimize memory effects, following Barkan and Luz (2005) we injected and discarded a minimum of four injections when switching between waters with a difference in d18O value of greater than 5.0 %. The cold fingers were sealed using a bellows valve.
The O2 samples were warmed to 60 C and expanded for 10 min into the sample bellows through a custom multiport on a dual-inlet ThermoFinnigan MAT 253 isotope ratio mass spectrometer (Thermo Electron, Bremen, Germany) with Faraday cup amplifiers for m/z 32, 33, and 34 of 1*109 Ω, 1*1012 Ω, and 1*1011 Ω, respectively. The custom designed multiport used air-actuated bellows valves, air pressure control originally intended
for a stock microvolume, and modified ISL scripts. The O2 sample was analyzed for m/z 32, 33, and 34 abundance ratios to determine d18O and d17O values with reference to O2 gas (d17Omeasured s/VSMOW=4.319%0.009, d18Omeasured s/VSMOW=8.255%0.002). Each mass spectrometric measurement comprised 90 sample-to-reference comparisons. Each of these comparisons consisted of 26 s of integration and 15 s of idle
time. After every 30 comparisons, the m/z 32 signals of the sample and reference gases were balanced to 10 V and the mass spectrometer was peak-centered on m/z 33. The reference bellows was automatically refilled before each sample to a pressure that was equal to that of the sample. Over the course of these measurements the mass spectrometer exhibited an internal reproducibility of 0.002 %, 0.004 %, and 0.0037 % (3.7 per meg) for d17O, d18O, and 17Oexcess values, respectively.
see Schoenemann et al. 2013.
- O. Abe. Isotope fractionation of molecular oxygen during adsorption/desorption by molecular sieve zeolite. Rapid Commun. Mass Spectrom. 2008, 22, 2510.
- E. Barkan, B. Luz. High precision measurements of 17O/16O and 18O/16O ratios in H2O. Rapid Commun. Mass Spectrom. 2005, 19, 3737.
- L. Baker, I. A. Franchi, J. Maynard, I. P. Wright, C. T. Pillinger. A technique for the determination of 18O/16O and 17O/16O isotopic ratios in water from small liquid and solid samples. Anal. Chem. 2002, 74, 1665.
- E. Barkan, B. Luz. Diffusivity fractionations of H216O/H217O and H216O/H218O in air and their implications for isotope hydrology. Rapid Commun. Mass Spectrom. 2007, 21, 2999.
- Schoenemann SW, Schauer AJ, Steig EJ. 2013. Measurement of SLAP2 and GISP d17O and proposed VSMOWSLAP normalization for d17O and 17Oexcess. Rapid Commun. Mass Spectrom. 2013, 27, 582–590.