Determination of δD and δ~(18)O values in ground water by the combination of thermal conversion elemental analyzer (TC/EA) and isotope ratio mass spectrometry

摘要

Measurement of the ~(18)O/~(16)O and D/H ratios in water is one of the most important applications of isotope ratio mass spectrometry, of which wide diverse applications such as variations in natural abundance in hydrologic cycle, the authenticity control on beverages, the use of ~(18)O enriched tracers in human and animal metabolic studies and geochemical deuterium content in natural water are greatly influenced by the history of water samples. An online continuous-flow method, combining a thermal conversion elemental analyzer (TC/EA) with isotope ratio mass spectrometry, was used for the determination of δD and δ~(18)O values in groundwater samples from various regions in Turkey. The technique involves reduction of H_2O by the reaction of glassy carbon at high temperature, which produces H_2 and CO at 1450 ℃. The gases were separated in a gas chromatography and analyzed by a mass spectrametry configured to make hydrogen and oxygen isotope analyses in continuous flow mode. The δ~(18)O and δD ratios were determined by monitoring the d~2H/~1H permil vs VSMOW and d~(18)O/~(16)O permil vs VSMOW. Two standards with a given δD and δ~(18)O values were used for calibration. The ranges in groundwater were found to be from -36.85 %o ± 1.12 to -67.68 %o ± 2.06 for δD and from -4.96 %> ± 0.24 to -10.87 %o ± 0.53 for δ~(18)O. Uncertainty budget and method validation are also presented.