3.4 Water hydrogen and oxygen isotopes test
The hydrogen and oxygen isotopic composition of water was determined by Gasbench Ⅱ-IRMS continuous flow. The constant temperature sample tray temperature was 28 ℃, the poraplot Q chromatographic column temperature was 70 ℃, and the He pressure was 120 kPa.
For δD-H2O analysis, the water sample was packaged in a 2mL chromatographic bottle, covered with a hollow cap and placed on the sample rack. Hydrogen isotope in water was measured by high temperature pyrolysis method. The flow rate of carrier gas He was 100 mL/min, the temperature of reaction tube was 1380 ℃, and the furnace temperature was 75 ℃. Then the hydrogen isotope was measured by Delta V advantage isotope mass spectrometer. The calibration curves of hydrogen isotopes in water were established by inserting standard samples with different abundances before and after the samples.
For δ18O-H2O analysis, 200 μL water sample and standard water were taken and put into a 12 mL (labco) reaction bottle, and the cap was tightened. Then the air blowing needle was fixed, the working procedure of the automatic sampler was set, 0.3% of CO2 + He mixture was filled in and inflated for 5 minutes to take the air from the bottle. After the completion of the filling, the water sample was kept in equilibrium for 18 hours, so that it could reach the equilibrium of isotope exchange. The CO2 isotope ratio after the equilibrium of isotopic fractionation was determined by Delta V advantage isotope mass spectrometer with fixed injection needle.