The analysis of the stable hydrogen and oxygen isotope composition of water using cavity ring-down spectroscopy (CRDS)
instruments utilizing infrared absorption spectroscopy have been comprehensively tested. However, potential limitations of infrared
spectroscopy for the analysis of highly saline water have not yet been evaluated. In this study, we assessed uncertainty arising from elevated salt concentrations in water analyzed on a CRDS instrument and the necessity of a correction procedure. We prepared various solutions of mixed salts and separate solutions with individual salts (NaCl, KCl, MgCl₂, and CaCl₂) using deionized water with a known stable isotope composition. Most of the individual salt and salt mixture solutions (some up to 340 g L−1) had δ-values within the range usual for CRDS analytical uncertainty (0.1‰ for δ¹⁸O and 1.0‰ for δ²H). Results were not compromised even when the total load of salt in the vaporizer reached ∼38.5 mg (equivalent to build up after running ∼100 ocean water samples). Therefore, highly saline mixtures can be successfully analyzed using CRDS, except highly concentrated MgCl₂ solutions, without the need for an additional correction if the vaporizer is frequently cleaned and MgCl₂ concentration in water is relatively low.