>Hi all,

I am working on 13C and 18O of carbonates.
As my samples are including a lot of organic matter,I wander what is
the best  technique to remove OC from the sample.Is still 5% sodium
hypochlorite compound and/or vacuum roasting only approved methods.
Many thanks
Lidia


>Alexander,
>We've found that using a kel-f disc between the septa and vial works very
>well with small CO2 samples. The sheets of Kel-f we buy are sold in
>fractions of an inch. We buy sheets by the square foot that are ten
>thousands of an inch thick. ALlTECH sells a septa punch that works well for
>cutting the Kel-f discs.
>
>hope that helps,
>Lowell Stott
>Univ. Southern California
>
>-----Original Message-----
>From: Stable Isotope Geochemistry [mailto:[log in to unmask]]On
>Behalf Of Alexander Knohl
>Sent: Sunday, February 18, 2001 6:24 AM
>To: [log in to unmask]
>Subject: [ISOGEOCHEM] atmospheric CO2 and gasbench
>
>
>hello All,
>
>I am working on 13C and 18O of atmospheric CO2, which are sampled in 10
>ml vials and analysed with a Finnigan Delta XL
>IRMS in combination with an autosampler and a Finnigan Gasbench. So far
>I have used several septa (silicone, teflon and the
>standard septa that comes with the labco vials) with different
>treatments (heated, evacuated, equilibrated with atmospheric air) but
>still see a large change in time for the 18O signature (ca. 0.2 promille
>per day).
>Can anyone recommend a septa that would work with low concentration of
>CO2 in small vials. Suggestions would be greatly
>appreciated.
>
>Thanks
>
>
>Alexander Knohl
>
>
>_______________________________________________
>
>Alexander Knohl
>Max-Planck-Institute for Biogeochemistry
>P.O. Box 10 01 64
>07701 Jena
>Germany
>
>phone:  ++49 3641 643727
>fax:    ++49 3641 643710
>email: [log in to unmask]

--

Lidia Bednarek
WABC & Botany Department
The University of Western Australia
35 Stirling Highway
Crawley 6009
Western Australia
Ph: (08) 9380 2213
Fax:(08) 9380 1001

West Australian Biogeochemistry Centre (WABC)
http://www.botany.uwa.edu.au/wabc