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

We have optimized the method of water fluorination using the solid reagent CoF3 to produce O-2. This allows isotope ratio measurements by dual-inlet mass spectrometry with very high precision of 0.01 to 0.03 parts per thousand for both delta O-17 and delta O-18. Using this method, delta O-17 and delta O-18 of atmospheric O-2 were determined as 12.08 and 23.88 parts per thousand vs. VSMOW, respectively. Likewise, delta O-17 and delta O-18 of GISP were -13.12 and -24.73 parts per thousand, and for SLAP they were -29.48 and -55.11 parts per thousand vs. VSMOW, respectively. Analysis of these data in a ln(delta O-17 + 1) vs. ln(delta O-18+ 1) plot yields a line with a regression coefficient (lambda) of 0.5279 +/- 0.0001 (R-2 = 0.999999). We also determined the fractionation factors 17 alpha and 18 alpha in liquid-vapor equilibrium, and found that the ratio In 17 alpha/ln(1) 8 alpha is constant (0.529 +/- 0.001) over the temperature range 11.4 to 41.5 degrees C. Copyright (c) 2005 John Wiley & Sons, Ltd.