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