Hi Again--

You should also check out Glaser and Amelung, Rapid Communications in
Mass Spectrometry, 2002;16:891-898 for a good discussion of limitations
and ways to work around them.  They are using fluorinated derivatives in
their work.  Also check out the references listed in there for the
actual set up (Brand J Mass Spectrom 1996; 31:225 and Merritt, et al.,
Anal. chem. 1995; 67:2461)...

take care

gerry

Gerard Olack wrote:

> 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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>