If your D31 palmitic acid is indeed 100% deuterium labeled you would 
only see mass 4 (D2+) and some fragment ions at mass 2 (D+). Mass 4 will 
be a huge peak, as large as the usual mass 2 peak (H2+) for the 
non-labeled acid. If you have some hydrogen (protium) left in your 
palmitic acid, most of it will show as mass 3 (DH+). I suspect that 
there is probably quite a lot of this, which will saturate the mass 3 
channel. Moreover, gas chromatography for these H-substituted palmitic 
acids will be smeared a bit, which is why I would expect a broader GC 
peak for mass 3. You would probably not see this prominently on the 13C 
peak.
Regards    Willi




On 5/20/2016 17:16, Marilyn Fogel wrote:
> Are all of the hydrogens in the molecule deuterium? If so I don't think this is a chromatography issue.
> I am not sure how the collector will handle a completely deuterated compound. Perhaps others will chime in.
> Marilyn Fogel
>
> Sent from my iPhone
>
>> On May 20, 2016, at 7:56 AM, Isabelle Chery <[log in to unmask]> wrote:
>>
>> Hello all,
>>
>> I would like to analyse a uniformly labelled fatty acid with Deuterium (D31 Palmitc Acid) after derivatization to be volatile as methyl ester by Gc pyrolyse IRMS.
>> I use a Zebron ZB Wax capillary GC column to separate different Fames (C14:0 to C22:0). The injector is at 220°C and the high temperature conversion reactor is at 1420°C.
>> The D31-Palmitic acid is totally separated from the natural Palmitic acid by GC.
>> I have beautiful peaks for natural abundance of FAMEs (mass 2 and mass 3) but for the D31-Palmitc acid, the peak shape (only mass 3 is present) is trailing and is not symmetric.
>> I have changed the insert, the syringe, cut the column, and put a new reactor tube. But the problem is always being.
>> Does anyone could help me?
>> Thanks
>> Isabelle
>>
>> <Test.pdf>

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Willi A. Brand, Stable Isotope Laboratory      [log in to unmask]
Max-Planck-Institute for Biogeochemistry (Beutenberg Campus)
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P.O.Box 100164,      07701 Jena, Germany
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