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Stable Isotope Geochemistry

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Subject:
From:
Dr W Meier-Augenstein <[log in to unmask]>
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Date:
Thu, 5 Feb 2004 08:54:57 -0000
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Dear Sean and others interested in the question of ionisation efficiency
for H2,


One (read: I) should never guesstimate or should from the hip. Thanks to
a private e-mail from Paul Brooks, I took (a) the time and (b) pencil to
paper for a "proper" calculation.

Assuming all things being equal (such as the final flow rate feeding the
source as opposed to flow rates in the peripherals; mistake #1) and
complete conversion, adjusting for mol equivalents (i.e. 1 mol
equivalent of water generating 1 mol equivalent of H2 and NOT 0.5;
mistake #2; stupid boy!), I now end up with a ratio of H2 : CO2 of 1 :
100; 100 nmol of H2 gives me a peak area of 1 Vs while 100 nmol of CO2
would give me 100 Vs. Obviously, nobody injects such copious amounts of
carbon into their system but 1 nmol of methylpalmitate (yielding 17 nmol
of CO2) generate a peak area of about 17 Vs.

Paul reckons the ratio should be 1 : 200, so I still seem to be out by a
factor of 2 but at least I'm in the right ball park (same order of
magnitude), and, as I said I made a number of simplifying assumptions.

So, my apologies for the misleading prior message to the list.


Cheers,

Wolfram

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