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

ABSTRACT 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 O 2 was analyzed on a Thermo MAT 253 for the paired δ 17 O‐δ 18 O value (Δ′ 17 O). Although the δ 18 O and δ 17 O values were variable, the fluorination reaction progresses along a slope of ~0.528, indicating that the Δ′ 17 O is constant when calculated using a λ ref = 0.528. The 18 O/ 16 O ratio was obtained using a TC/EA, and the δ 17 O value was corrected based on the measured Δ′ 17 O value from fluorination and the δ 18 O values obtained on the TC/EA. Results We provide δ 17 O, δ 18 O, and Δ′ 17 O 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′ 17 O 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 δ 17 O, δ 18 O, and Δ′ 17 O 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′ 17 O measurements when paired with δ 18 O values using the TC‐EA technique.