New Ag₃PO₄ comparison material for stable oxygen isotope analysis

Abstract

Rationale A silver phosphate reference material (Ag3PO4) for the measurement of stable oxygen isotope compositions is much needed; however, it is not available from the authorities distributing reference materials. This study aims to fill this gap by calibrating a new Ag3PO4 stable isotope comparison material produced by the University of Natural Resources and Life Sciences (BOKU). Methods Aliquots of Ag3PO4 were distributed to four laboratories who frequently measure the δ18O value in Ag3PO4; the University of Natural Resources and Life Sciences (BOKU), the University of Western Australia (UWA), the University of Helsinki (UH), and the Helmholtz Centre for Environmental Research (UFZ). The instruments used to perform the measurements were high‐temperature conversion elemental analysers coupled with continuous flow isotope ratio mass spectrometers. The working gas δ18O value was set to 0‰ and the normalization was done by a three‐point linear regression using the reference materials IAEA‐601, IAEA‐602, and NBS127. Results The mean δ18O value of the new BOKU Ag3PO4 comparison material on the VSMOW‐SLAP scale is 13.71‰ and the combined uncertainty is estimated as ±0.34‰. This estimated uncertainty is within the range typical for comparison materials of phosphates and sulphates. Consistent results from the different laboratories probably derived from similar instrumentation, and use of the same reference materials and normalization procedure. The matrix effect of the different reference materials used in this study was deemed negligible. Conclusions The BOKU Ag3PO4 can be used as an alternative comparison material for stable oxygen isotope analysis and is available for stable isotope research laboratories to facilitate calibration.

Oxygen isotope ratios of phosphates in the soil‐plant system: Limitations and future developments

“…We believe silver phosphate would be a good candidate because it fulfills these requirements. In addition, silver phosphate is a very stable compound, easy to degas and not hygroscopic, featuring additional benefits to use this material as an international reference standard (Fourel et al, 2011; Lécuyer et al, 2007; Watzinger et al, 2021).…”

Oxygen Isotopes in Carbonate and Phosphate of Modern Mammal Bioapatite: New Data and Critical Revision after about 25 Years from the First Recognitions

“…Calibration was done using the standards IAEA-601, IAEA-602, and NBS 127 (barium sulphate) and the "quality control" using the standard AGPO-SCRI (14.6‰ ± 0.2‰, standard deviation, against 14.58‰ ± 0.13‰ [48]) and NIST SRM 120c (22.9‰ ± 0.2‰ against 21.79‰ ± 0.15‰, [48]). The values obtained by Halas et al [49] and by Watzinger et al [49] for NIST SRM 120c are apparently significantly different (p (same average) < 0.005); it is noteworthy, however, that analyses reported in literature for NIST SRM 120c are largely variable ( [48] and references therein).…”

“…More recently, Watzinger et al [49] reported oxygen isotope analyses carried out in four different laboratories on a new silver phosphate sample (BOKU Ag 3 PO 4 ) with 13.71‰ ± 0.34‰ (combined standard uncertainty). Calibration was done using the standards IAEA-601, IAEA-602, and NBS 127 (barium sulphate) and the "quality control" using the standard AGPO-SCRI (14.6‰ ± 0.2‰, standard deviation, against 14.58‰ ± 0.13‰ [48]) and NIST SRM 120c (22.9‰ ± 0.2‰ against 21.79‰ ± 0.15‰, [48]).…”