Stable isotopes of oxygen and hydrogen in water: analytical method evaluation and the determination of δ¹⁸O and δ²H on a control sample

Evaluation studies contribute to the identification of parameters that can affect the accuracy and precision of analytical methods. This study describes the analysis of δ¹⁸O and δ²H in water samples by the equilibrium method at the Isotope Geology Laboratory (LGI), Center for studies in Petrology and Geochemistry (CPGq) of the Federal University of Rio Grande do Sul (UFRGS). For that, six batches of analyzes were carried out under different ambient temperature conditions. For the reproducibility tests, four aliquots of the control sample were analyzed at the Polar Climate Center (CPC). Results showed that ambient temperature did not significantly affect the accuracy of the oxygen analysis. However, the mean result at 20 °C showed greater accuracy and acceptable precision. Hydrogen analyzes at a room temperature of 18 °C showed an external standard deviation and an internal precision exceeding the recommended, while at 20 and 22 °C the results were statistically acceptable, being the first more accurate. From that, it is possible to conclude that the determination of δ¹⁸O and δ²H in water at the LGI, employing the equilibrium method at an ambient temperature of 20 °C, showed satisfactory repeatability and reproducibility.

Keywords:
stable isotopes; H and O; analytical method; water