Isotopically characterised N O reference materials for use as community standards.

RATIONALE

Information on the isotopic composition of nitrous oxide (N O) at natural abundance supports the identification of its source and sink processes. In recent years, a number of mass spectrometric and laser spectroscopic techniques have been developed and are increasingly used by the research community. Advances in this active research area, however, critically depend on the availability of suitable N O isotope Reference Materials (RMs).

METHODS

Within the project Metrology for Stable Isotope Reference Standards (SIRS), seven pure N O isotope RMs have been developed and their N/ N, O/ O, O/ O ratios and N site preference (SP) have been analysed by specialised laboratories against isotope reference materials. A particular focus was on the N site-specific isotopic composition, as this measurand is both highly diagnostic for source appointment and challenging to analyse and link to existing scales.

RESULTS

The established N O isotope RMs offer a wide spread in delta (δ) values: δ N: 0 to +104‰, δ O: +39 to +155‰, and δ N : -4 to +20‰. Conversion and uncertainty propagation of δ N and δ O to the Air-N and VSMOW scales, respectively, provides robust estimates for δ N(N O) and δ O(N O), with overall uncertainties of about 0.05‰ and 0.15‰, respectively. For δ N , an offset of >1.5‰ compared with earlier calibration approaches was detected, which should be revisited in the future.

CONCLUSIONS

A set of seven N O isotope RMs anchored to the international isotope-ratio scales was developed that will promote the implementation of the recommended two-point calibration approach. Particularly, the availability of δ O data for N O RMs is expected to improve data quality/correction algorithms with respect to δ N and δ N analysis by mass spectrometry. We anticipate that the N O isotope RMs will enhance compatibility between laboratories and accelerate research progress in this emerging field.