We once used our GC Isolink for nitrogen isotope analyses of amino
acids and could not measure accurate d15N values on our laboratory
reference compounds. With two GC-C III interfaces in the laboratory,
this was not a major issue and now do all our amino acid nitrogen
isotope analyses on instruments interfaced via a GC-C III. As with
you, we get up to 100 injections before the reactor tube is spent
(Pt, Ni, 4 x Cu wires) on the GC-C III. End of life can come on very
suddenly and the best gauge of when the end is near is the accuracy
of the d15N value which we assess with internal reference compounds
injected with every sample and by analysis of a suite of ~12 amino
acid reference compounds, which are analyzed every fourth injection.
Yes, that is not many samples especially when analyzing collagen,
which require a total of six injections (3 at dilute concentration
and 3 at high concentration with the large peaks backflushed).
We have used our GC Isolink for carbon isotope analyses of amino
acids. Coupled to the 253, the peak shapes that we get are
unbelievably sharp. So far, we have not exhausted a GC Isolink
reactor tube before it has sprung a leak. Normally, we get hundreds
of injections before the leak is manifest.
Matt McCarthy and I have drowned our sorrows in far too many beers
bemoaning the difficulty with nitrogen isotope analyses of amino
acids (but we continue both the analyses of the beer drinking).
Please join us next meeting. I insist on at least triplicate
analysis of each sample and I suspect you feel the same way given
the difficulty of obtaining accurate and precise nitrogen isotope
analysis of amino acids. I have some ideas why the GC Isolink did
not return accurate d15N values on our reference compounds but we
are happy to use our GC-C III and with the cost of the GC Isolink
reactor tubes it is more economical.
It would be more economical to build your own GC Isolink reactor
tube and it would be wonderful if somebody could share their
secretes on how these are constructed and where to obtain the
Hope this helps.
On 10/1/2014 12:27 PM, Marilyn Fogel
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At $600 per reactor, a 2 week time frame is troubling. I hope
more folks chime in. We need more information on performance.
Ours has lasted about 4 months, mostly carbon, but about 100
Any symptoms that might tell the reactor is going, other than
I have found the lifetimes to be considerably better than
the GC-C-III oxidation reactors, albeit a bit variable. I
have had one last 3 months. I had one last only two weeks.
On average, I'd say about 1.5 months. For us, that would be
600-700 injections, either 13C or 15N, mostly 15N.
For 15N, periodic "seed oxidation" is critical.
Unfortunately, the timing of the seed oxidation required to
maintain quality combustion varies as the reactor ages, with
increasing frequency required for older reactors.
I've experimented with making my own copy of the new
reactor and have found a suitable nickel tube, but need to
re-visit the union. Not sure if anyone has had success with
rolling their own, yet, but I'd love a recipe.
Brian N. Popp, Professor
University of Hawaii, SOEST, Department of Geology & Geophysics
1680 East-West Road, Honolulu, Hawaii 96822
Office - (808) 956-6206; Fax - (808) 956-5521