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.