Dear Hans,
Thanks for your email re platinum sticks. It
is very useful to make contact with the manufacturer of the
platinum sticks.
We use platinum sticks placed in 5 ml vials with a
septa on the top. The platinum stick is placed in the vial so that it is half in
and half out of the water. We were told at one time that the equilibration took
place at the water/gas interface but have also been told that it takes place in
the vapor phase. When we tried to put the sticks entirely in the vapor phase, we
had less success than when the sticks were half in and half out. Do you sell
anything that keeps the sticks out of the water? We tried making stainless steel
holders but these seemed to work poorly.
On a slightly different note, we also analyse plant and
soil water that has been extracted using a distillation process with kerosene
(aviation gas). There are small traces of solvent in the water and this also
seems to contaminate the sticks or somehow cause problems with equilibration.
For these samples we currently analyse by reducing the water to hydrogen
over heated depleted uranium (works well but not an automated system). I'm
hoping that by putting the sticks in the vapor phase, we can run these using the
equibration method.
Looking forward to hearing from you.
Regards,
Fred
to the water equilibration people,
just a reminder, the isotope equilibration between H20 and H2 happens in
the vapor phase , so if there is no H2S in the vapor (depending on the pH of the
liquid ) then there is no poisoning of the catalyst surface. But if you do have
H2S in the vapor phase the catalyst will be inactive with time. And a second
reminder: the equilibration occurs on the catalyst surface the catalyst has to
be temperature controlled . some people place the catalyst well above the liquid
phase at the top of a bottle where the temperature might be different by a few
tenth of a centigrade compared to the temperaturecontrolled liquid and
therefore they get different fractionation results. and a third thing: do not
stop bacterial activity with HgCl2 this ruins the catalyst
Hans Friedrichsen
for
MS Analysentechnik (producer of the catalyst
sticks)
-----Ursprüngliche Mitteilung-----
Von: Jonathan Wynn
<
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An:
[log in to unmask]Verschickt: Di., 15.
Jan. 2008, 19:15
Thema: [ISOGEOCHEM] poisoning of D/H platinum rods/Hokko
Beads by dissolved sulfide, and copper pre-treatment
Hi
All,
I've read in the ISOGEOCHEM archives that the Platinum
catalyst used in D/H analyses of H2O by equilibration can be "poisoned" by
dissolved sulfides. Does anyone have experience to estimate a sulfide
concentration above which this effect should be considered significant? I've
also read about pre-treatment with copper to avoid this problem. Does anyone
have a reference or advice for a standard
pre-treatment?
Thanks,
Jonathan
Wynn
Department of Geology
University of South
Florida
4202 E Fowler Ave, SCA 528
Tampa, FL
33620
Tel. +1 (813) 974-9369
Lab. +1 (813)
974-5278
Fax. +1 (813) 974-2654
[log in to unmask] http://shell.cas.usf.edu/~jwynn 
