Greg and other sulfate-oxygen people,
We are using a TC/EA set up with a Delta Plus XL for running d18O-SO4 with
reasonable success. I am interested if any other users of the same
equipment have experienced any of the same problems we have though. We have
less memory problems when we run at higher temperatures (>1400C), but, it
appears at higher temperatures we begin to damage the ceramic tube and/or
the glassy carbon tube after a couple hundred samples. We have not run
enough other "stuff" to determine if the problem is just with SO4 or if
water, NO3, etc. might also cause problems regardless of temperature.
Anyhow, we start to accumulate a yellowish crystalline substance on the
outside of the glassy carbon tube at approximately the level of the
combustion. We scrape this stuff off when we clean out the crucible (~200
samples). But eventually it gets thick in spots and then the ceramic starts
to get a clear glaze on the outside at about the level of combustion. We've
had fine cracks then develop and then larger cracks until the ceramic tube
ends up breaking. We have thought that maybe the S is poisoning the tube at
high temperatures?? Has anyone else seen this with or without SO4 samples?
We've mainly run pure BaSO4 precipitates, some barite minerals, jarosite,
alunite, etc.
As far as how to actually do the analysis, we basically follow the TC/EA
manual for recommended flow rates, temps, etc. we have the reactor set
1400-1450C and the GC at 90C. We weigh about 0.3 mg BaSO4 into a silver
cup.
Does anyone have insight on the mystery crystalline-goo?
thanks,
Cyndi
**************************************************************
Cyndi Kester
Ecologist--Stable Isotope Lab
U.S. Geological Survey
Denver Federal Center, Bldg. 21, MS 963
Denver, Colorado 80225
office: 303-236-0278
lab: 303-236-7694
fax: 303-236-4930
email: [log in to unmask]
----------
>From: "Gregory A. Wandless" <[log in to unmask]>
>To: [log in to unmask]
>Subject: Sulfate oxygen by on-line pyrolysis EA
>Date: Wed, Jan 3, 2001, 11:41 AM
>
> I am looking for references or any other information on doing sulfate
> oxygen isotopic
> analysis by on-line pyrolysis EA. Any suggestions?
>
> Thanks,
> GAW
>
> --
> =======================================
> Gregory A. Wandless
> Chemist
> US Geological Survey
> MS954
> Reston, VA 20192
>
> Email:[log in to unmask]
> Phone: (703) 648-6189
> =======================================
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