18O in water is analyzed using the method described below. Although we can analyze as little as 25 uL water, this amount is hard to work with so we would recommend at least 200 uL and preferable 1 mL. Please contact us directly for shipping instructions and time needed for analysis.
Paul D. Brooks and Todd E. Dawson.1
1Center for Stable Isotope
Biogeochemistry, Department of Integrative Biology, MC 3140, 3060 Valley Life Sciences, University of
California - Berkeley, CA 94720-3140 USA. Tel + 1 1 (510) 643-1748, FAX +1 1 (510) 643-1749,
Email isotopes@berkeley.edu.
In brief: 200 uL of water for both standards and samples are pipetted into 10 mL Exetainers and quickly
sealed. The Exetainers are then purged with 0.2% CO2 in Helium and allowed to equilibrate at room
temperature for at least 48 hours. The 18O in the CO2 is then analyzed on a Thermo Delta Plus XL mass
spectrometer, using a Thermo Gas Bench II. Different sizes of water samples can be analyzed by preparing
complete sets of standards and samples with the same water volume, down to 100 uL. For volumes less than
100 uL, the Exetainers are purged first with the 0.2% CO2 in Helium, and then the water sample is added
with a syringe through the Exetainer septa, and allowed to equilibrate for 5 days. This will work for
volumes down to two drops, (about 20 uL) after which the water all evaporates in the Exetainer tube.
GAS Bench II operating manual, ThermoQuest, Oct 1999.
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