I'm interested in the low temp combustion approach, and would consider
separate runs for 13C (low temp) and d15N (high temp).  I'm really not a
fan of sample pretreatment if it can be avoided. Also, by evaporating the
HCl of my sample I know I will be left with chlorides that may interfere
with EA analysis.

What temperatures do you analyze at? I was going to lower the EA temp to
~600°C and try analyzing peach leaves, IAEA-C5 and IAEA-C3 and see how
thing look. Do you still use the Cu reduction furnace at 650°C?

thanks,
Toti.

  At 05:31 AM 7/7/2005, you wrote:
>We've been using thermal analysis attached to an IRMS system for just
>this problem (intimately intergrown calcite and soil organic matter).
>This approach exploits the fact that generally SOM degrades at lower
>temperatures than carbonates decompose, and we can 'easily' distinguish
>del13C for calcite from that of cellulosic material and lignin-derived
>material.
>
>The only snag would be that siderite's thermal decomposition is at
>lower temperatures than calcite, so the job ecomes a bit harder.
>
>Also, we can't do N at the present time - but that's the next step in
>the development of this system.
>
>Get in touch if you'd like to send us a couple of samples to try.
>
>David Manning
>
>
>
>On 6 Jul 2005, at 19:00, tlarson wrote:
>
>>Folks,
>>
>>We're trying to separate siderite from soil/clay samples so that we may
>>analyze the organic components of the soil for d13C, d15N and CN
>>ratios.
>>The refs I've come across focus on 'carbonate' removal and indicate
>>that
>>siderite is less soluble. I found I can dissolve siderite in 6 molar
>>HCl at
>>50°C overnite, or soaking in 6 molar HCl at 25°C for several days. To
>>remove excess HCl I plan to freeze dry the samples and not pour out
>>any of
>>the acid in case some of the organics have also gone into solution (I
>>think
>>this is the same idea as vapour removal).
>>
>>Any comments or suggestions regarding possible effects others have
>>observed
>>using this method, or better methods before I follow the tedious path
>>of
>>sample preparation testing? The first line of testing I was going to
>>do was
>>to dose IAEA-C5 (wood) with siderite and see if THIS pretreatment
>>affected
>>its d13C values.
>>
>>Thanks in advance for saving me time,
>>
>>Toti.
>>
>>
>>Toti Larson Ph.D.
>>Los Alamos National Laboratory
>>Earth and Environmental Sciences                505.667.9894 (lab)
>>Los Alamos, New Mexico 87545            550.667.8006 (office)
>>
>Professor of Soil Science
>School of Civil Engineering and Geosciences
>University of Newcastle
>Newcastle upon Tyne
>NE1 7RU
>
>telephone (+44) 0191 222 7893

Toti Larson Ph.D.
Los Alamos National Laboratory
Earth and Environmental Sciences                505.667.9894 (lab)
Los Alamos, New Mexico 87545            550.667.8006 (office)