A versatile water vapor generation module for vapor isotope calibration and liquid isotope measurements

A versatile vapor generation module has been developed for both field-based water vapor isotope calibrations and laboratory-based liquid water isotope measurements. The vapor generation module can generate a stream of constant vapor at a wide variety of humidity levels spanning 300 to 30 000 ppmv and is fully scalable, allowing in principle an unlimited number of standards or samples to be connected to a water vapor isotope analyzer. This versatility opens up the possibility for calibrating with multiple standards during field deployment, including examining instrument humidity-isotope dependence. Utilizing the ability to generate an uninterrupted constant stream of vapor, we document an Allan deviation for .sup.17 O-excess (Î.sup.17 O) of less than 2 per meg for an approximate 3 h averaging time. For similar averaging time, the Allan deviations for [delta].sup.17 O, [delta].sup.18 O, [delta]D, and d-excess are 0.004 0/00, 0.005 0/00, 0.01 0/00, and 0.04 0/00, respectively. Measuring unknown samples shows that it is possible to obtain an average standard deviation of 3 per meg for Î.sup.17 O and an average standard error (95 % confidence limit) of 5 per meg.