I will reply at the risk of being thought to be ³snarky². The Gas Bench is
a great invention, but like you¹ve pointed out, water gets on the septum,
then into very expensive needles, migrates into expensive valves and is in
general a Pain in the A$$.
My suggestion if you really have a lot of water samples to run: get one of
the new laser instruments. My favorite (opinion) is the Los Gatos, which
works like a charm for water samples of many different types.
Understanding that you might not have this capability, I prefer the TCEA
for H and O in water samples‹straight conversion rather than equilibration
which continues to have some voodoo attached to it.
Regards, Marilyn Fogel
On 10/31/16, 11:16 AM, "Stable Isotope Geochemistry on behalf of Raquel
Mingote" <[log in to unmask] on behalf of [log in to unmask]>
>We are using the equilibration method H2/CO2 - water with GasBech
>(CF-IRMS) for d18O and d2H in water. USGS LIMS is used for drift
>correction, normalization and data management.
>We observed that the sample condenses in the septum, which can increase
>the carry of water to the GasBench. The temperature of GasBench is 28 oC
>and the room temperature 24 oC. We are working with the minimum of 18
>hours equilibration.The background m/z=18 is increasing to high values,
>until 15000 mV after the run. Usually we are carrying the baking of the
>GC Column (120 oC) ,as suggested by paper of Rangarajan and Ghosh
>(2011), after the batch of samples. We are monitoring the background of
>m/z=18 before and after the run for d18O.
>We appreciate all comments about this issue.
>Rangarajan R. and Ghosh, P.; Role of water contamination within the GC
>column of a GasBench II peripheral on the reproducibility of 18O/16O
>ratios in water samples. Isotopes in Environmental and Health Studies, v.
>47, n. 4, 498-511, 2011.