The first IAEA inter-laboratory comparison exercise in Latin America and the Caribbean for stable isotope analyses of water samples

ABSTRACT

The use of stable isotopes (δ²H and δ¹⁸O) is widespread in water resources studies. In the Latin America and the Caribbean (LAC) region, the application of isotope techniques has increased in the past decade, but there remains room to gain self-reliance in environmental isotope studies, necessitating easy and fast access to good-quality isotope data. To that end, in 2018 the IAEA carried out the first regional interlaboratory comparison exercise, testing the analytical performance of 25 laboratories using isotope-ratio mass spectrometry and laser absorption spectroscopy. The three test samples covered a commonly observed range of 0 to –16 ‰ δ¹⁸O and 0 to –115 ‰ δ²H. z- and ζ-scores were used to benchmark laboratories’ performance against a strict criterion. We found that 81% of the laboratories had satisfactory performance ($\overline{\left|z\right|}$≤ 2) for δ²H but only 54% achieved similar scores for δ¹⁸O. Only a minor fraction of results (12% for δ²H and 15% for δ¹⁸O) were unsatisfactory. The larger number of questionable results for δ¹⁸O confirmed the challenges in laser absorption spectroscopy for this isotope. Besides instrumental performance, the sample throughput, laboratory reference materials, and data post-processing were contributing factors to inaccurate or imprecise performance.

KEYWORDS:

• Hydrogen-2
• IAEA
• interlaboratory comparison
• isotope hydrology
• Latin America
• oxygen-18
• water

Acknowledgements

This proficiency test would not have been possible without the generous cooperation of researchers and staff in 25 stable isotope laboratories located in Latin America and the Caribbean region. We thank T. Chavez for assistance organising international sample shipment, and M. Denecke as well as two anonymous reviewers for their comments and improvements to the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by the International Atomic Energy Agency. We thank the IAEA Technical Cooperation Programme for their support of this activity under project RLA/7/024.