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Thu, 22 Dec 2005 13:50:07 -0500 |
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I am trying to decide on the lesser of evils regarding elimination of
inorganic C before 13C determination on solid samples by mass spectrometer.
Our samples are Oklahoma soils. They don't fizz when acid is dropped and
they all have less than 0.2% gravimetric CaCO3 equivalent. But because this
level of inorganic C could still raise the 13C content by 4 per mil I would
like to compare the 13C content of treated vs untreated soils.
Browsing the archives I find that HCl or H2SO3 treatments are preferable to
H3PO4 or the HF treatments. The Harris et al (2001) HCl fumigation is,
however, purported to consume some organic C and thereby alter the 13C
content of the remaining organic matter, whereas the Verardo
et al (1990) H2SO3 method is purported to damage the analyzing equipment.
Is it clear that the Verardo et al method -- in which 0.4 ml of 8% sulfurous
acid is added to each capsule -- is more aggressive on the mass spectrometer
than the HCl fumigation with 12M HCl?
Can someone please outline the appropriate adjustments to the Verardo et al
method (e.g. using use Ag, not Al, capsules?). And, is there any reason why
one can't fumigate with H2SO3 instead of dropping it in each capsule several
times? If fumigation is plausible, what strength is recommended?
Thanks very much
-Cristina
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