An on-line technique for the determination of the delta O-18 and delta O-17 of gaseous and dissolved oxygen

摘要

Few studies have used the stable isotopic composition of O-2 as a tracer of gas transport or biogeochemical processes in environmental research. Here we demonstrate field sampling techniques for gaseous and dissolved O-2 and describe an analytical method for measuring delta(18)O and delta(17)O values of O-2 in air, soil gas, and water samples using continuous-flow isotope-ratio mass spectrometry (CF-IRMS). A Micromass CF-IRMS was altered to accommodate a sample gas injection port prior to a CO2 and H2O trap and GC column. The GC column was 1-m, 5-Angstrom molecular sieve column held at 35 degrees C. The resolved sample O-2 was introduced to the IRMS via an open split. delta(18)O and delta(17)O values were determined by measurement of O-2 isotopes at m/z 34/32 and 33/32 and comparison to a reference pulse of Oz. Repeated injections of atmospheric oxygen yielded a repeatability (+/-SD) of +/-0.17 parts per thousand for delta(18)O and +/-0.5 parts per thousand for delta(17)O. IRMS source linearity was excellent for O-2 over a sample size range of 60-400 mu L. The smallest sample for routine delta(18)O and delta(17)O determinations was similar to 80 mu L of O-2, With a Sample analysis time of 180 s, Preliminary results from a riverine and soil gas study illustrate natural oxygen isotope fractionation processes. [References: 9]