Could I add one word of caution on the subject of soil combustion?

In our limited experience, combustion efficiency and more to the point
reactor performance / life span seem to very much depend on the type of
soil.

I'm not a soil specialist so can't really make any qualified comment on the
nature / composition of the soil that we were asked to run but I did notice
that reactor life span in terms of number of samples run was very much
reduced when analysing soils from a site in England (sorry, not allowed to
say which county).

Instead of being able to run, say 250 samples of 'normal' organic material
(approx 0.4 mg per capsule) reactors packed up after 100 samples already due
to what looked like sintering or 'glass' formation inside the reactor. Based
on this observation I do not know if obsidian (which is already glass) is a
good proxy for soil, i.e. sand (SiO2) mixed with alkaline minerals (e.g.
sodium and calcium carbonates) thus containing all the ingredients to make
soda-lime glass.

I'm not happy when I see things like this happening because impaired reactor
performance usually means skewed isotope ratios be it because of
non-quantitative sample conversion or be it because of changes in mass flow.

So, running reference materials or house standards at a much higher
frequency than one would otherwise seems like a good safety precaution to
monitor reactor performance and, hence trustworthiness of results from soil
combustion.


Regards,

Wolfram




> -----Original Message-----
> From: Stable Isotope Geochemistry 
> [mailto:[log in to unmask]] On Behalf Of Anthony L. Michaud
> Sent: 21 February 2007 15:21
> To: [log in to unmask]
> Subject: Re: Good soil combustion
> 
> We had an undergraduate student doing a variety of 
> experiments to test the EA efficiency (varied temperature, 
> sample size, amount of C/N, amount of acid to add to soils to 
> remove inorganic C, etc.) last year. I would like to put 
> those results on our webpage (or the wiki page), but I first 
> need to let him write it up and present it.
> 
> One test we performed to check on the combustion efficiency 
> of low C,N samples was to take a peach leaf standard and add 
> powdered obsidian (no C or N content) to it to verify that 
> isotope ratios were ok with samples as big as about 45mg. I 
> don't see why this experiment couldn't be carried out to 
> 200mg. I can send you some of the data if you'd like to give 
> you an illustration of what we did.
> 
> Hopefully I'll be able to post the student's results in the 
> next month or two. The data are more than one year old now...
> 
> Anthony
> 
> 
> ------------------------------------------------------
> Anthony L. Michaud
> W. M. Keck Foundation Laboratory for Environmental 
> Biogeochemistry School of Earth and Space Exploration Arizona 
> State University Tempe, AZ 85287-1404
>  
> Web: http://kfleb.asu.edu
> Tel: 480-727-8033
> Fax: 480-965-8102
>  
> Mailing address:
>  
> Anthony Michaud
> PSF-686
> Arizona State University
> Tempe, AZ 85287-1404
>  
> ***Windsurf Everywhere***
> ------------------------------------------------------
>  
> -----Original Message-----
> From: Stable Isotope Geochemistry 
> [mailto:[log in to unmask]] On Behalf Of Isabelle Billy
> Sent: Wednesday, February 21, 2007 2:47 AM
> To: [log in to unmask]
> Subject: Re: [ISOGEOCHEM] Good soil combustion
> 
> Dear all,
> 
> I 'm so concerned, as we have often the same problem with 
> some sediment wich are very poor in N (0.02%), so I'm really 
> interesting in the answer, as I often doubt that we have a 
> good combustion with 100 or 200mg sample.
> 
> 
> Ruben G. Chavez a écrit :
> 
> >Dear all,
> >
> >I am analyzing SOIL NC in EA and I need at least 75ugN in 
> the sample to 
> >get
> a 
> >good linearity. With this amount of N I need, I need to 
> weigh up to 200 
> >mg
> of 
> >finely ground sample due to low %N in the sample. Please 
> help me on how 
> >to know if I have a good combustion of the sample. Is there 
> a specific 
> >combustion catalyst for plant or soil combustion?
> >
> >Many thanks for your help.
> >
> >
> >Ruben G. Chavez
> >Officer
> >Analytical Service Laboratories
> >Mail: DAPO Box 7777, Metro Manila, Philippines
> >Tel: +63(2) 580-5600 ext. 2419
> >Fax: +63(2) 580-5699
> >Web: www.irri.org
> >
> >  
> >
> 
> --
> Isabelle Billy
> UMR EPOC - 5805
> Département de Géologie et Océanographie Université de 
> Bordeaux I avenue des facultés
> 33405 TALENCE Cedex, France
> 
> email [log in to unmask]
> 
> tel. (33) 05 40 00 33 14
> fax (33) 05 40 00 08 48
>