Hi Paul,
I thought you might join the discussion on this subject.
You are absolutely right in saying that working with Ag capsules has its
disadvantages (build-up of silver droplets and resulting impact on He flow
and quality of 2H data; unless one has a reverse-flow setup such as
Willie's).
That said, one of our student tried to run precipitated AgNO3 in tin
capsules for 18O and the results were a disaster. Perhaps, this was more a
reflection of how diligent the precipitate was prepared and washed but I
still don't fancy repeating this experience.
I had a go at using tin capsules with more benign samples at T > 1400 C and
the results and the blank didn't give much cause for concern at first.
However, I noticed a pronounced 'dulling' of the glassy carbon (tube and
chips) which I think was responsible for poor results in subsequent runs.
Not being made of money, we recycle our reactors (by scrubbing and cleaning
the glassy carbon), which with silver capsules works quite well. Reactors
are good for 500+ samples. The whitish-grey coat left behind when using tin
capsules was not easily removed (for a brief moment I considered a wash
with KOH but resisted temptation) is virtually impossible to remove by
scrubbing and renders the reactor useless after <200 sampless.
So, for the time being I continue using silver capsules despite the silver
build up lowering our sample through put rate.
Best regards,
Wolfram
On Jul 19 2006, Paul Brooks wrote:
> Tim,My understanding is that the silver has a lower blank than tin, as
> presumably the surface of the tin is tin oxide. However, in working with
> a low temperature furnace (1130C) for organic O, the tin capsules worked
> better. For reasons unknown, as silver builds up in the reactor the
> difference between the high and low standards decreases, and the middle
> standard does not fall on a straight line between them. With tin this is
> not a problem, for reasons unknown.For at least 1mg samples of cellulose
> the dilutor on our Conflo II is set fairly high, and there is no
> significant difference between the silver or tin blanks.I have heard of
> TC/EA users having to suck out the silver from the furnace every 70
> samples or so. This means that high temperature furnaces may also suffer
> from the same problem. Has anyone tried tin capsules with a high
> temperature furnace?Paul Brooks.At 08:37 AM 7/19/2006, you wrote:
> Greetings...Is anyone running a TC/EA using tin capsules for loading
> samples instead of silver capsules? I am wondering why people use silver
> so often on the TC/EA...is it that there might be some oxidation of the
> tin capsules which may contaminate samples? If so is there not the same
> fear with silver, or does silver not oxidize to the same extent as
> tin?Thanks...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] for Stable Isotope
> Biogeochemistry Valley Life Science Building Room 3060 Integrative
> Biology - MC3140 Berkeley CA-94720 Phone: (510)-643-1748 Fax:
> (510)-643-1749
|