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Marilyn

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 stuffing.

Hope this helps.

Brian

On 10/1/2014 12:27 PM, Marilyn Fogel wrote:
> 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 injections N.
>
> Any symptoms that might tell the reactor is going, other than the obvious?
>
> Marilyn
>
> From: Chris Yarnes <[log in to unmask] <mailto:[log in to unmask]>>
> Reply-To: Stable Isotope Geochemistry <[log in to unmask] 
> <mailto:[log in to unmask]>>
> Date: Wed, 1 Oct 2014 14:50:48 -0700
> To: <[log in to unmask] <mailto:[log in to unmask]>>
> Subject: Re: Longevity of Isolink GC reactors
>
> Hi Marilyn,
>
> 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.
>
> Chris
>
> On Wed, Oct 1, 2014 at 12:15 PM, Marilyn Fogel <[log in to unmask] 
> <mailto:[log in to unmask]>> wrote:
>
>     Dear isogeochemists,
>
>     We have a relatively new GC Isolink system that we've been using
>     for N isotopes in amino acids. I have no experience with the
>     reactors (or their cost). Could anyone give me a sense of how many
>     injections or samples are typically run through one of these
>     Isolink reactors before they need to be changed?
>
>     I am familiar with the approx. 100 injections from the GC-C
>     interface III, in which a homemade reactor can be easily replaced,
>     but not the fancy new one.
>
>     Marilyn
>
>     Dr. Marilyn L. Fogel, Professor of Ecology
>     Chair, Life and Environmental Sciences Unit
>     Faculty Director, Environmental Analytical Laboratory
>     President Elect, AGU Biogeosciences
>     School of Natural Sciences
>     University of California at Merced
>     5200 Lake Rd., Merced California 95343
>     Phone: 209-205-6743 <tel:209-205-6743>; FAX: 209-228-4646
>     <tel:209-228-4646>
>
>
>
>
> -- 
> Chris Yarnes, Ph.D.
> Stable Isotope Facility 
> <http://stableisotopefacility.ucdavis.edu/index.html>
> Department of Plant Sciences
> Univ. of California-Davis
> One Shields Ave., MS 1
> Davis, Calif. 95616
> 530-754-7517
>
> Compound-specific stable isotope analysis 
> <http://stableisotopefacility.ucdavis.edu/compoundspecific.html>
> Sulfur stable isotope analysis 
> <http://stableisotopefacility.ucdavis.edu/34s.html>
>
>
>

-- 
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
http://www.soest.hawaii.edu/GG/people/gg_profile_popp_b_html