At 09:43 AM 2/06/98 MET-1MEST, you wrote:
>Dear list memebers !
>
>Anyone out there experiencing the same problems ? As the quartz
>reactor tubes for the reduction and oxidation reactors of my
>elemental analyzer quite easily break upon removal of catalysts, I
>turned to stainless steel tubes. I used one of these to
>contain the reduction catalysts, the oxidation one was still made of
>quartz.
>The carbon and nitrogen contents as well as the carbon isotopic
>results were quite fine, very reproducible and correct. However, the
>delta15N values were false showing numbers being 50 to 80 permille
>versus atm-air too high. This problem did not dissapear upon
>analysing 250 samples with the same reactor, but immediately vanished
>when switching back to the quartz tubes.
>Are there possibilities to deactivate the steel column ? Are there
>steel qualities, which don't give rise to such problems ?
> Please help, otherwise I'll have to return the tubes back to the
>producer. Thanks in advance,
>
>Wolfgang
>Dr. Wolfgang Wanek
>Department of Chemical Physiology of Plants
>Institute of Plant Physiology
>University of Vienna
>Althanstraáe 14
>A-1091 Vienna, Austria
>
>Tel: + 431 31336 1426
>Fax: + 431 31336 776
>Email: [log in to unmask]
>

Dear Wolfgang
Unfortunately I can not resolve your problem with steel tubes due I am
using quartz tubes, but this is the point. I am using the same tubes
several times (of course, nothing is for ever!) and they are working
properly, not broken. I remember a coworker in Scotland using Europa
Scientific E.A. who had the same problem, each time he has to replace the
chemicals he has to put new tubes. I am using a CarloErba machine but I
supose the problem has to be more related with the tube quality than with
the type of E.A. My suplier is Elemental Microanalysis. I am not sure if
may be important just before to introduce the tubes into the fournace I
clean them with CCl4 to remove any organic matter which would be burned on
the external tube surface damaging it.
I hope this may be on any help

Dr. Rafael Nuñez Gomez
Dpto. Ciencias de la Tierra y Quimica Ambiental
Estacion Experimental del Zaidin
Consejo Superior de Investigaciones Cientificas
Profesor Albareda 1, 18008 Granada, Spain
Tf 34-958-121011 Fax 34-958-129600
email: [log in to unmask]
http://www.eez.csic.es/~isotopos