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We too do not see issues with the normal quartz tubes on our RoboPreps and ANCA-SLs which use the Cr2O3, CuO and Ag wool combination. However, it is important to separate each packing with a 5 mm plug of glass wool. Especially at the join between the Cr203 and CuO - if the Cr203 is allowed to sit directly on the layer of CuO the quartz tube will start to break down at the join and leak.

The role of the silver at the bottom is to trap sulphur and halides. Carlo Erba used to always supply silvered cobaltous oxide for this purpose while Europa Scientific supplied CuO and silver wool as their standard. At the time (ca. 30 years ago) the choice came down to price (silver wool was cheaper) because they both worked as well as each other. It's also worth noting that the RoboPreps were developed first and foremost to be an integral part of a CF-IRMS system whereas the Carlo Erbas of the time (NA1500) were first and foremost stand alone elemental analysers. Hence there were subtle differences in their design including the quartzware and chemicals that they used.

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On 08/01/2016 11:36, Victor Evrard wrote:
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Dear Rolland,

Yes I meant Cr2O3.
I'm not sure my question was clear as I didn't mean to substitute Cr2O3 for CuO, a question that was already the topic of another thread.
I meant what is the difference between using CuO + Ag wool or instead silvered cobaltous oxide at the bottom of the oxidation reactor (which by the way is below the hot spot)? I have never had any issue with the quartz reactor in the CuO and Ag wool zone before.
Are there good reasons to choose one over the other (cost, material hazard, quality of the analysis...)?

Thanks,
Victor

On Tue, 5 Jan 2016 at 12:52 Roland A. Werner <[log in to unmask]> wrote:
Dear Victor,

I think it`s Cr2O3 and not CrO3.
And Cr2O3 is not the (main) oxidant (own experience: definitely not at all a quantitative CO production at 1450 °C with carbon reduction technique). According to Pella and Colombo (1973; Mikrochimica Acta [Wien] 1973, 697-719) the silver in the cobaltous oxide fraction gives a "better mechanical resistance" at temperatures >750 °C. The silver is additionally effective in "retaining halogens (except fluorine) and sulphur oxides". The Cr2O3 can easily be used "up to  temperatures of 1800-1900 °C".
Many years ago we used a Roboprep system, similar to the Sercon system you described, with  a similar filling with a.o. CuO. Sometimes (often ?) we had problems with leakage at the point where CuO and quartz come in contact (possible reason --> building of an eutectic system  between <SiO2> and <CuO> ??) depending also on quartz quality and applied temperature (problems were solved by introducing a Ni sheet). CuO easily releases O2 at higher temperatures; I think already at temperatures > 800°C, which would reduce the life-time of the filling of the oxidation reactor and could lead to not constant oxidation conditions and a reduced life-time of the reduction tube.
There is an interesting review article (in German) about the "history" (with e.g. pros and cons of catalysts etc.) of elemental analysis by I. Monar in Microchimica Acta, Heft 2 (1965), 208-249.
Best regards

Roland

####################################
Papers in 2015:

The relationship between needle sugar carbon isotope ratios and tree
rings of larch in Siberia
(free access at the moment)
http://treephys.oxfordjournals.org/cgi/reprint/tpv096?ijkey=LNjo87Wp2OvIpbZ&keytype=ref

Malate as key carbon source of leaf dark-respired CO2 across different
environmental conditions in potato plants (free access)
http://jxb.oxfordjournals.org/content/66/19/5769.full.pdf+html

Allocation dynamics of recently fixed carbon in beech saplings in
response to
increased temperatures and drought (free access)
http://treephys.oxfordjournals.org/content/35/6/585.full.pdf+html?sid=4454cd3b-b5c1-4575-9075-44da4e4abfea

Multifactorial in vivo stable isotope fractionation: causes, correlations,
consequences and applications (limited free access)
http://www.tandfonline.com/eprint/DEZ3TmbQqvUqVFqqm7as/full
in case if the pdf is not available anymore pls check on researchgate:
http://www.researchgate.net/profile/Roland_Werner/

Changes in d13C of dark respired CO2 and organic matter of different
organs during early ontogeny in peanut plants (limited free access)
http://www.tandfonline.com/eprint/6WUmBtH42ZHUAVr46IXN/full
in case if the pdf is not available anymore pls contact me per email

Multi element (C, H, O) stable isotope analysis for the authentication
of balsamic vinegars (limited free access)
http://www.tandfonline.com/eprint/DEZ3TmbQqvUqVFqqm7as/full
in case if the pdf is not available anymore pls contact me per email

Editorial "Special Issue dedicated to Prof. Hanns-Ludwig Schmidt on the occasion
of his 85th birthday" (open access)
http://www.tandfonline.com/eprint/I2hIdGxU8yZIcJ2VIiRV/full
in case if the pdf is not available anymore pls contact me per email

Does fog chemistry in Switzerland change with altitude?
(in case you are interested pls send an email)
http://www.sciencedirect.com/science/article/pii/S0169809514000866


Special issue dedicated to Prof. Hanns-Ludwig Schmidt
http://www.tandfonline.com/toc/gieh20/51/1


####################################

Dr. Roland A. Werner
Institut fuer Agrarwissenschaften
Massenspektrometer-Labor
ETH Zuerich, LFW C48.1
Universitaetsstrasse 2
CH-8092 Zuerich
Schweiz

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        Academia.edu Account
        https://independent.academia.edu/RolandWerner
####################################

On 05.01.2016 12:25, Victor Evrard wrote:
Dear All,

After working with Sercon systems and now Thermo systems for EA-IRMS, I have been meaning to ask this question regarding the suggested use of CrO3+Silvered cobaltous oxide and CrO3+CuO+Ag wool for the oxidation reactor by Thermo and Sercon, respectively.
What is the difference?

Thank you and happy new year!
Victor
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Victor Evrard, PhD
Lab Manager | BASIEL

Sustainable Land Use Group | Department of Environmental Sciences
University of Basel
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