HI Alexandre--

I've not played with this directly, but a couple of things you'll need
to be concerned about:
1. You'll need to derivatize the amino acids for GC analysis.  This is
another source of carbon, and...
2.  Standard derivatizations usually involve a fluorinated carbon chain,
e.g. trifluoroaceto group.  Finnigan recommends you avoid running
halogens through their GCC furnace since you'll form metal halides and
poison the reactor.

I did run across a couple of articles that may be of interest.  I've not
gone over them in detail, but the first one could be of general interest
for GC-SIRMS of amino acids, the second one is more focused on your
interests
Amino acid derivatization:
*CHARACTERIZATION OF N-ETHOXYCARBONYL ETHYL-ESTERS OF *AMINO*-*ACIDS* BY
MASS-SPECTROMETRY  *HUANG ZH, WANG J, GAGE DA, WATSON JT, SWEELEY CC,
HUSEK P
JOURNAL OF CHROMATOGRAPHY 635 (2): 271-281 APR 16 1993
PHE characterization:
*THE DETERMINATION OF LOW D(5)-PHENYLALANINE ENRICHMENT (0.002-0.09 ATOM
PERCENT EXCESS), AFTER CONVERSION TO PHENYLETHYLAMINE, IN RELATION TO
PROTEIN-TURNOVER STUDIES BY GAS-CHROMATOGRAPHY ELECTRON IONIZATION
MASS-SPECTROMETRY,* CALDER AG, ANDERSON SE, GRANT I, MCNURLAN MA,
GARLICK PJ, RAPID COMMUNICATIONS IN MASS SPECTROMETRY 6 (7): 421-424 JUL
1992

take care

gerry

p.s. yeah, you'll have to do test runs on at least the main amino acids
of interest:  analyze them in bulk, analyze the derivatization reagent
in bulk and analyze the derivatized amino acid in bulk and by GC-SIRMS.
The combustion should be complete in your GC reactor as long as it's not
overloaded/poisoned and you don't have something thats hard to burn.
However you can always get some fractionation in the injector port or
potentially anywhere there is a dirty split.  And don't forget, your
pulse of CO2 gas coming form the combustion of the sample will be
accompanied by pulses of N2 and H2O, also from sample combustion.  The
N2 isn't removed and sample drying is never perfect.


Alexandre Myre wrote:

> Hi everybody !
>
> We are planning on analysing amino acide (PHE) of muscles using a
> GC-IRMS system but haven't worked out what standard to use yet. We
> have been told to use only internal standard (home made amino acid
> solution with a desired range of 13C/12C isotopic ratio) to build a
> calibration curve to correct the samples isotopic ratios.
>
> Doing so implies that the CO2 analysed after the combustion of the
> standard in the furnace has the same exact isotopic composition as
> that of the amino acid in the standard solution. Theoritically, the
> combustion should be total and the isotopic ratios should be
> conservative but is it the case ?
>
> The ideal would be of using a calibrated amino acid solution (of known
> isotopic composition) to correct the samples and the internal stds for
> their absolute values but is that what people usually do ?
>
> Thanks in advance for any hints !
>
> Alexandre
>
> Research Officer, Université Laval, Québec
>
>
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