ABSTRACT

Hydrogen and oxygen isotopic analysis using an off-axis integrated-cavity output spectroscopy (OA-ICOS) was carefully checked for long-term stabilities, dependence on the injected water volume, inter-sample memory effects, and influence of salinity, with an aim to investigate whether it can be an alternative to conventional isotope ratio mass spectrometry (IRMS). Salinity (up to 4 wt.% NaCl) had no influence on measured values of δD and δ¹⁸O, therefore the OA-ICOS technique can be applied to the analysis of seawater without demineralization. Standard errors (1σ) of δD and δ¹⁸O analysis using this technique were typically 0.2–0.3‰ and 0.05–0.10‰, respectively, which are completely comparable to those of conventional dual-inlet IRMS methods. The results suggest that the OA-ICOS method can be an alternative of IRMS for δD and δ¹⁸O analysis of natural water. However, sporadic fluctuations of measured values were often encountered. This problem can be most likely ascribed to subtle individual differences in the quality of micro-syringes used.