High precision measurements of 17O/16O and 18O/16O ratios in H2O

Abstract
We have optimized the method of water fluorination using the solid reagent CoF3 to produce O2. This allows isotope ratio measurements by dual‐inlet mass spectrometry with very high precision of 0.01 to 0.03‰ for both δ17O and δ18O. Using this method, δ17O and δ18O of atmospheric O2 were determined as 12.08 and 23.88‰ vs. VSMOW, respectively. Likewise, δ17O and δ18O of GISP were −13.12 and −24.73‰, and for SLAP they were −29.48 and −55.11‰ vs. VSMOW, respectively. Analysis of these data in a ln(δ17O + 1) vs. ln(δ18O + 1) plot yields a line with a regression coefficient (λ) of 0.5279 ± 0.0001 (R2 = 0.999999). We also determined the fractionation factors 17α and 18α in liquid‐vapor equilibrium, and found that the ratio ln17α/ln18α is constant (0.529 ± 0.001) over the temperature range 11.4 to 41.5°C. Copyright © 2005 John Wiley & Sons, Ltd.