Gas Bench δ18O water method description for analyses done at UCSC SIL.
Oxygen isotopic compostion of water was determined by equilibrium exchange of the water oxygen with 0.3% carbon dixoide gas in a predominantly helium headspace environment. A continuous He flow Gas Bench headspace sampling interface is used to dry and isolate the CO2 gas for introduction into a ThermoFinnigan Delta Plus XP isotope ratio mass spectrometer. Analyses were run at the University of California, Santa Cruz Stable Isotope Laboratory. Analytical precison of internationally calibrated in-house standards is better than 0.06 permil for d18O. Sample isotopic values are corrected for drift and source stretching effects.