HI All--
Tim, do you have the graphite funnel in place on top of the glassy C
tube? Also, is the crucible in the hot zone, and are the capsules
falling into it? We've had some poor yields and drawn out peaks when
the capsule lands on top of
the glassy C tube or crucible. Same if the reactor packing is a bit
off and the
crucible is sitting up too high. Yeah, we reuse the crucible until they start
to fall apart--then make our own by drilling out a graphite electrode rod
(alpha aesar).
It may also be time to bake out the GC column, and then check the Conflo for
build up of the "yellow gunk" in the sample open split and
contamination of the
line going to the mass spec. Oh yeah, we've been getting better results using
2%H2 in He for the carrier gas instead of just He, but He is ok.
Robert, the "scavenging oxygen problem" (for me) refers to the big drop in
yields when you try to run silver phosphate after barites using the same
reactor. Barites after phosphates are ok, and you can run either after
cleaning and repacking the reactor.
take care
gerry
Quoting Robert Van Hale <[log in to unmask]>:
>
> Hi Tim,
> I'm diverging from the thread here, but would you please describe the
> "scavenging oxygen problem" with barium sulphate for me please. I have often
> noted a lower CO yield from BASO4 than from other standards - I wonder if
> this relates to what you speak of?
> Cheers
> Robert Van Hale
>
>> -----Original Message-----
>> From: Stable Isotope Geochemistry
>> [mailto:[log in to unmask]] On Behalf Of Tim Prokopiuk
>> Sent: Thursday, 9 March 2006 11:20
>> To: [log in to unmask]
>> Subject: [ISOGEOCHEM] TC/EA Furnace Rerevisited
>>
>> Greetings again...
>>
>> Thanks to all for the information (Marilyn, Jon, Wolfram)
>> concerning a dying TC/EA oven. To clarify a little further
>> what we are observing:
>>
>> In the glassy carbon reactor we have only run benzoic acid,
>> potassium nitrate and silver phosphate, so no divalent
>> cations that I know of have ever been loaded. We ran into
>> the scavenging oxygen problem with the barium sulphate
>> standard and quickly stopped using it many months ago. But
>> what is strange about our current situation is that we had
>> two runs silver phosphate that ran well, and now suddenly
>> silver phosphate won't run properly. We've tried twice
>> repacking the column with fresh glassy carbon fragments, and
>> the reactor is quite new (maybe only a couple hundred samples
>> run through it before this occurred). I initially had
>> thought of a spent column, or that maybe the packing wasn't
>> quite right (a gap in the glassy carbon fragments maybe), but
>> this does not seem to be the case.
>>
>> When we run benzoic acid or KNO3 and plot signal intensity
>> vs. mass I get a straight line. When I try to run AgPO4 and
>> plot this it looks like a shot gun blast. The d18O values
>> that show the expected yields all look good, but those that
>> fall below are depleted, so I am definitely losing oxygen
>> somewhere. Those values that are low show peak tailing (my
>> lost oxygen most likely): the sign of a spent reactor. But
>> the very next sample or two might run perfectly with good
>> numbers...this does not sound like a spent reactor.
>>
>> I did notice on my water reactor that the hot zone
>> discoloration is in a very narrow zone now...I think I recall
>> that earlier in the life of the furnace the hot zone on the
>> glassy carbon reactors was larger?
>>
>> Another question: how many times are people reusing their
>> graphite crucibles? We flame ours to clean out the silver
>> buildup and then reuse them. Maybe after a few times they
>> become less reactive somehow??
>>
>> Any other takers?
>>
>> Tim Prokopiuk
>>
>>
>> -------------------------------------------------
>> Tim Prokopiuk
>> B. Sc. Geology/Technician
>> Saskatchewan Isotope Laboratory
>> Room 241
>> Department of Geological Sciences
>> University of Saskatchewan
>> 114 Science Place
>> Saskatoon, Saskatchewan, Canada
>> S7N 5E2
>> Phone: (306) 966-5712
>> Fax: (306) 966-8593
>> Email: [log in to unmask]
>>
>
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