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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.

Steve

Steven Brookes, PhD
Director
-- 
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On 08/01/2016 11:36, Victor Evrard wrote:
> 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] 
> <mailto:[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
>
>     Tel. Buero:  ++41/(0)44/632 6754
>     Tel. IsoLab: ++41/(0)44/632 6694
>
>     e-mail:[log in to unmask]
>     <mailto:e-mail:[log in to unmask]>
>
>     URL:    Personal ETH website
>              http://www.gl.ethz.ch/people/person-detail.html?persid=116463
>              Researchgate Account
>              http://www.researchgate.net/profile/Roland_Werner/
>              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
>>     --
>>     Victor Evrard, PhD
>>     Lab Manager | BASIEL
>>
>>     Sustainable Land Use Group | Department of Environmental Sciences
>>     University of Basel
>>     Schönbeinstrasse 6
>>     CH-4056 Basel
>>     Switzerland
>>
>>     http://goo.gl/cl6x97
>>     +41 61 267 35 17
>