Stable Isotope Geochemistry


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Gerard Olack <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Sat, 9 Jul 2005 11:30:59 -0400
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HI Bill--

There was some discussion earlier this year on the list about DIC
(preservation and storage, std storage around 1/26/05 and 5/11/05, e.g.
[ISOGEOCHEM] DIC std storage and sample collection from Daniel Doctor
was the last comment in one series I think).  Also, if you go with
longer equilibration times, you may want to shake down/flick to the side
some of the condensation that collects on the septa prior to analysis.

One of my colleagues asked about doing 18O along with 13C for 13C from
DIC and 18O from the water.  Does anyone know about particular problems
with that?  We're just planning on trying 100%phosphoric and long
equilibration times--along with seperate water and DIC standards.
Thanks in advance.

Good luck Bill--

take care


Anthony M. Faiia wrote:

>We have been running lake waters for DIC with concentrations around 15ppm C. It is based upon the Gas Bench DIC procedure for ocean waters and gives reproducible results (std dev=0.15 permil). Our procedure differs in that we inject more water than for ocean samples. We use 5mL and also remove some of the helium from the exetainer before injection of water. The removal of He gives a better response for the mass spec and makes it much easier to inject 5mL. You might be able to get away with a lower He pressure when flushing instead or evacuate the containers instead as Noah suggested. The detailed procedure follows.
>1. Prepare gas bench vials for sampling.
>        add 150uL of phosphoric acid (H3PO4) to vial
>        cap vial
>        flush vial with helium using Gas Bench for 5 minutes at 100mL/min flow
>2. Sample water.
>        rinse 15mL syringe with sample
>        fill syringe with 6mL of water
>        keep syringe vertical and remove 5mL of helium from vial
>        inject 5mL of water sample into vial, leaving 1mL of water as air lock in syringe
>3. Analyze DIC.
>        put samples in Gas Bench tray at 25ˇăC
>        wait at least 1 hour
>        run mass spec sample sequence for measurement of DIC
>--- You wrote:
>Hi all,
>Can anyone direct me to a reference (or give some advice) on using the gas
>bench to analyze DIC in ground waters? I have a student who would like to
>make some measurements this summer, but we have not tried this on the gas
>bench and would prefer not to reinvent the wheel.
>--- end of quote ---