Preparation and Certification of Reference Materials for Hydrogen and Oxygen Isotopes in Water

Certified reference materials of water for stable hydrogen and oxygen isotopes were developed and have been used for more than 30 years. However, they no longer meet the requirements for newly developed technologies. New reference materials of water have been developed, including three natural water samples and one artificially deuterium depleted water sample and are discussed in this paper. The three natural water samples mostly cover the range of δ¹⁸O and δD values for the majority of natural water in China. 30 ampoules were selected randomly from the 5000 ampoules for homogeneity test and each sample was measured twice. According to the homogeneity test results, no statistically significant heterogeneity was found based on the F test. The verified results by variance analysis for four material samples showed very good homogeneity for the series. Nearly two years of stability analysis of δ¹⁸O and δD values confirm that they have no statistically significant instability. The certified values of the reference materials were determined by an inter-laboratory comparison of 11 participating laboratories, using different measurement methods and instruments. Uncertainty assessment was performed. The δD value of the reference materials was determined by the chromium-reduction method, H₂-H₂O equilibration using platinum as a catalyst, laser-based stable isotope measurement, and high-temperature conversion/elemental analysis-isotope ratio mass spectrometry (elemental analyzer systems; IRMS). The δ¹⁸O value of the reference materials was determined primarily by the classic CO₂-H₂O equilibration method. The expanded uncertainties at the 95% confidence level of δ¹⁸O were less than 0.08‰ and δD was less than 0.9‰. The reference materials were approved as certified reference materials by AQSIQ, China (State General Administration of the People’s Republic of China for Quality Supervision and Inspection and Quarantine) in 2012. The serial numbers are GBW 04458-GBW 04461.