Hello Dachun,

I have not seen such large differences with our EA-Isoprime system or
our Microgas-Isoprime system when the peak intensities are between
approximately 3.5 and 13nA (using a 200 Trap).  However, when there
is <3 nA of gas linearity does become a problem, particularly when
using the microgas.  My guess is that there is a problem with the
source.  You might want to play with your source tuning.  If this has
changed recently I suggest going back to the original values and see
if you have linearity.  If all else fails try to run samples that are
all the same size (...make sure you have stability though).  This is
not the best solution, but it will do until you discover why there is
a linearity problem.

Good luck,
Jennifer



>Hi,
>
>I found the d13C value changes of the same sample with different size. A
>typical example: when the peak intensity is 1.45, 3.13 and 11.28 nA, the
>d13C will be -26.78, -24.44 and -23.98. The reference gas linearity is
>great. Anybody has similar experiences? I use IsoPrime running oil samples.
>
>Cheers.
>
>Dachun Zhang
>Zymax


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Jennifer Mckay
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GEOTOP - Universite du Quebec a Montreal
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