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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:
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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 injections N.

Any symptoms that might tell the reactor is going, other than the obvious?

Marilyn

From: Chris Yarnes <[log in to unmask]>
Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
Date: Wed, 1 Oct 2014 14:50:48 -0700
To: <[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]> 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



--
Chris Yarnes, Ph.D.
Stable Isotope Facility
Department of Plant Sciences
Univ. of California-Davis
One Shields Ave., MS 1
Davis, Calif. 95616
530-754-7517

Compound-specific stable isotope analysis
Sulfur stable isotope analysis




-- 
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