2023 Volume 30 Issue 1 Pages 3-12
Future investigations associated with disposal projects will require analysis of groundwater or pore water samples with small volumes, high ion concentrations, and high particulate and organic matter content. Hydrogen-oxygen isotopes can provide important information for understanding the migration behavior of groundwater and are currently often analyzed by wavelength-scanned cavity ring-down spectroscopy (CRDS), where salinity, particulates, and organic matter can interfere with accurate quantification. In this study, we investigated a method to remove salt and particulates as a pretreatment for the CRDS measurements. An experimental system for distillation with small amount was constructed, and the optimum conditions for recovery of the samples after distillation were determined. From the results of the isotopic ratio analysis in the samples before and after distillation, it was confirmed that the distillation method was suitable for analyzing the isotope ratio of samples with high salt and inorganic particle content. On the other hand, distillation of muddy water samples containing a large amount of organic matter resulted in a shift in hydrogen isotope ratios. The method of generating water vapor from the sample solution at room temperature and analyzing the water vapor (direct water vapor measurement: DWVM) was also investigated. It was confirmed that the DWVM was also capable of accurately quantifying the hydrogen-oxygen isotopic ratio in samples with high salinity and high inorganic particle content. In the case of mud samples containing a large amount of organic matter, it was found that the hydrogen-oxygen isotopic ratio of the sample could be analyzed by DWVM when the percentage of mud contamination was up to 25 %.
