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

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 (|z|¯≤ 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.