Anthony,

You can use sodium bicarbonate as a working TIC standard, but the trick is
in keeping the solid dry. Ours has a value of -8.0 per mil, calibrated by
combustion on our EA.  I tested a small batch of this by baking it in a
drying oven overnight at 60 C.  After baking, the stuff had become enriched
to about -4 per mil.  No surprise, since it is only baking soda after all.
The moral: use a desiccator, not a drying oven. But, you may be able to
shoot for the value you want by careful baking and re-calibration.

Sodium carbonate is another alternative, but I found that once a std
solution is mixed, the pH is too high for it to be stable, as it readily
absorbs CO2 from the atmosphere.  The sodium bicarbonate is much more
stable, and has been an excellent TIC std.

Dan

***********************************************
Daniel H. Doctor
Isotope Tracers Group
U.S. Geological Survey
345 Middlefield Rd, MS 434
Menlo Park, CA  94025

tel: 650-329-4544
fax: 650-329-4538




                      "Anthony L.
                      Michaud"                 To:       [log in to unmask]
                      <[log in to unmask]        cc:
                      >                        Subject:  TOC high standard?
                      Sent by: Stable
                      Isotope
                      Geochemistry
                      <[log in to unmask]
                      UVM.EDU>


                      05/10/2005 09:21
                      AM
                      Please respond to
                      Stable Isotope
                      Geochemistry






We are getting our working standards together for DIC/DOC using an OI
Analytical TOC analyzer coupled to a Delta Plus Advanatage. We’d like to
have a working standard that is somewhere around -5 to +5 permil vs PDB so
that it is close to our TIC values. Do any of the TOC-IRMS users out there
have suggestions on where I might find an ok standard that is so enriched?
Not much info in the archives concerning TOC standards…

Thanks for any help!

Anthony



------------------------------------------------------
Anthony L. Michaud
Physical Sciences F-686
Arizona State University
Tempe, AZ 85287-1404

Tel: 480-727-8033
Fax: 480-965-8102

http://geopig.asu.edu/keck/index.html

***Windsurf Everywhere***
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