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Date: | Tue, 31 Jul 2007 09:48:27 -0400 |
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Yes, the zinc acetate/NaOH works well, and avoids the problems associated with Cd (CdCO3, Ca(OH)2 and haz-waste). But a few notes of caution:
1)Once you add the water sample to the ZnAce, you no longer have a homogeneous solution. Before going on to your next step, empty the entire container conents into your flask and then rinse the container with a bit of DI. Yes, this means you base concentrations on sample weight with all of the usual taring, etc.
2)No surprise, sulfides oxidize easily. The surprise might be how easily. Getting rid of the electron acceptors is a good thing. Boil the water, use glass containers (not plastic), etc. Zinc-sulfide seems pretty stable, so try to work with that as much as possible.
3)Remember that hydrogen sulfide is more toxic than hydrogen cyanide. The good news, the nose is VERY sensitive to H2S (until the concentration gets to high, but then you can stop worrying about it). I have yet to come across a GW where it was a problem, but use caution.
Pat McLoughlin
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From: Stable Isotope Geochemistry on behalf of River He
Sent: Mon 7/30/2007 1:37 PM
To: [log in to unmask]
Subject: [ISOGEOCHEM] Precipitation of dissolved sulfide in groundwater
Hi everyone,
We are working on a project about dissolved sulfide in
groundwater. I read some papers and it seems the
better way to precipitate sulfide in the field is to
use cadmium acetate.
I checked the original paper by Van Everdingen et al
(1982) and the chapter by Mayer and Krouse (2006)in
Handbook of stable isotope analyitcal techniques.
They all said that the PH values of water samples
should be adjusted to strongly basic conditions using
chemical like sodium hydroxide. We did some test but
found that soon sodium hydroxide is added into cadmium
acetate solution, the white milk color material begins
to precipitate (we pre-fill the sample bottles with
cadmium acetate and sodium hydroxide). We'd like to
know what the white milk color materials are and
whether they will have any impact on the sulfide
precipitation that follows and thus the final isotope
analysis.
Thanks in advance,
River He
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