Determination of the Absolute Hydrogen Isotopic Ratio of V‐SMOW and SLAP

By mixing 1 H 2 O and 2 H 2 O, both with accurately known purity, samples were prepared with 2 H/ 1 H ratios close to those of the international isotopic water standards: V‐SMOW and SLAP. A mass spectrometrical comparison of these calibration samples with the actual water standards revealed: 2 H/ 1 H of V‐SMOW = (155.95 ± 0.08) × 10 −6 2 H/ 1 H of SLAP = (89.12 ± 0.07) × 10 −6 δ 2 H V‐SMOW (SLAP) =−428.5 ± 0.5 %