High-precision measurements of water isotopes using laser absorption spectroscopy

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. © 2013, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.