I worried about formation of copper and nickel fluorides until I spoke with Marilyn Fogel who asked me how much fluoride really ends up going into the reactor tube with each compound? The answer is not a lot even though compound specific nitrogen isotopic analyses of amino acids requires high column loading. We have performed 100's of injections using a single reactor tube. Yes, they do not last as long as a reactor tube used strictly for compound specific carbon isotopic analysis of non-fluoride derivatives, but we found the benefits of TFAA outweigh the shortened reactor life.
We also found the thinkness of the stationary phase improves chromatography. The SGE BPX5 30 m x 0.32 mm id x 1 um gives excellent peak shape and separation for compound specific nitrogen isotopic analyses of amino acids. The chromatography was way better than we got using an HP Ultra2 50 m x 0.32 mm id x 0.5 um even though both are 5% phenyl, 95% methyl siloxane.
> My advice to you if you choose to accept it is NOT to use
> trifluoroacetylation to derivatize AAs. I know this is one of the
> best derivatization methods for AAs to obtain a sharp, well
> resolved GC chromatograms BUT it is also a sure-fire way to
> exhaust your oxidation reactor very fast and irreversibly (the
> formation of copper and nickel fluorides makes a re-oxidation