Fluorination of Silver Phosphate in Nickel Reaction Vessels for Triple Oxygen Isotope Analysis.

RATIONALE: Increasingly, more laboratories are measuring the triple oxygen isotope values of phosphate. Standardization is key to having good interlaboratory results. Here, we present the triple oxygen isotope values of a suite of standards using fluorination and compare them with previously reported triple oxygen isotope values. METHODS: Silver phosphate (~2-3 mg) was fluorinated in nickel reaction vessels, and the resulting O2 was analyzed on a Thermo MAT 253 for the paired δ17O-δ18O value (Δ'17O). Although the δ18O and δ17O values were variable, the fluorination reaction progresses along a slope of ~0.528, indicating that the Δ'17O is constant when calculated using a λref = 0.528. The 18O/16O ratio was obtained using a TC/EA, and the δ17O value was corrected based on the measured Δ'17O value from fluorination and the δ18O values obtained on the TC/EA. RESULTS: We provide δ17O, δ18O, and Δ'17O values for the following silver phosphate standards: NBS120c, USGS80, USGS81, AGLox, and B2207. Two new standards are also reported and available for distribution. To report our values on the VSMOW2-SLAP2 scale, we measured common silicate standards: San Carlos Olivine, NBS28, NMQ, and SKFS that have been calibrated to VSMOW2-SLAP2. Our reported Δ'17O error for silver phosphate is 10 per meg, calculated using the average long-term standard deviation of our two most replicated standards. CONCLUSIONS: We report the δ17O, δ18O, and Δ'17O values for a large suite of silver phosphate standards and present two new standards that can be used for interlaboratory calibration. Our results are reported on the VSMOW2-SLAP2 scale by measuring silicates on the same instrument with the same reference gas. The fluorination method in nickel reaction vessels is easily adapted to other laboratories that have fluorination lines. Only 2-3 mg of silver phosphate is needed for Δ'17O measurements when paired with δ18O values using the TC-EA technique.