Dear Uli, Paul and List,
With regard to the posting about GC-IRMS systems, funny how there is almost
a dead erie calm out there amongst the listmembers right now...So, a few
comments which may help (or not) some folks.

First, for as many investigators as there are doing GC-IRMS work, that is
how many different configurations there are in use.  Every lab I have
visited does things its own way and has worked out small details in
different ways to suit their particular sample needs.  So, my first opinion
would be that no one set-up fits all.

I have no experience on the Europa instruments, but I can comment on both
the FMAT and Micromass instuments.  Both do a fine job and will produce
good data.  I have had success with both and trouble with both.  This kind
of assesment usually only ever leads to a "grass is greener on the other
side" type of arguement.  In my opinion, you should focus on the interfaces
themselves and the software.

Again, different analyses require different set-ups for the best quality
data.  There are two ways to go here. The first is to have a system that
can be all things to all users...ie, one that will do C, N and H all
without undoing any fittings.  I prefer a more directed approach...starting
with one basic plumbing scheme and modifying it slightly for specific
analyses.  For example, using the reduction oven for N analysis, but
getting rid of it for C.  I simply prefer to have the minimal amount of
plumbing and connections in place for what ever analyses I want to do.
The "minimal plumbing" approach, I think, allows for maximum flexibility in
analyses, and ease of troubleshooting, especially when multiple users are
involved (ie, gradstudents).  For C and N, I have my own personal preferred
configuration.  It consists of a Valco valve in the GC oven for
"backflushing", a Ni/Pt reactor at 1000 oC with a O2 trickle and a nafion
dryer for water removal.  I like open spilt at the end of the reactor,
before the nafion dryer.  For N, two connections allows for the insertion
of the reduction reactor.  Most folks should recognize aspects of Finnigan
and Micromass systems in that configuration.

I have no experience with H2 systems yet.  But, I would again revert back
to the most simple plumbing possible to get the job done.  As I understand
it, both Fmat and Micromass do a good job with He mitigation in the IRMS
itself.

While I can build my own interface to meet my own analytical needs (and
most of you can too), I can't write the software.  I have long been a user
of the ISODAT system and the ISOCHROM software  for CDOS and OS2,
respectively.  I have only seen alpha versions of ISODAT-NT and have never
seen the latest MASSLYNX from Micromass.  You can have the greatest
hardware in the world, but if the software won't allow for background
corrections or standardization that you think is appropriate, you won't be
happy.  I hope to be in a position to purchase a system soon. and I am
going to want to thoroughly test drive the software packages for all of my
applications.

So, what to buy.  As far as hardware, I would argue that the simplest
plumbing will get you the most reliable results with minimum hassle. I
would wager that anyone who has had their instrument for a year or more
probably isn't running a stock system any more.  The analytical pitfalls
for real samples are always deeper than for baseline resolved standards. So
look for the instrument you think you can work on...not just to repair, but
to modify to push your own analytical envelope.  Visit labs you trust do
good work and see what they do.  Most folks are pretty accommodating and
love to show off how they have overcome the latest hurdle with some neat
trick.  As for the software, make sure you understand completely how it
does everthing.     Both software systems are relatively new and not very
user tested (if at all), so I would check them out very thoroughly before
you buy.

Clear as mud...Bob Dias





[log in to unmask]@LIST.UVM.EDU on 12/07/2000 06:03:16 AM

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Subject:  [ISOGEOCHEM] GC/C/IRMS machines


Dear listmembers

I for one would like to know what users think about certain manufacturer's
machines (so would they probably)!
Let's not keep it to ourselves. The whole point of the list is to have
information passed on to other listmembers.

So hopefully someone will come up with some thoughts/info on the GC/C/IRMS
combinations and put it on the list.

Thanks
Paul
--


Paul Kennedy

Marine Science Laboratories
Stable Isotope Group
University of Wales - Bangor
Askew Street
Menai Bridge
Anglesey LL59 5EY
United Kingdom

email: [log in to unmask]
tel: + 1248 388116
fax: + 1248 716367

http://www.sos.bangor.ac.uk/OceanScience/research/stable_isotope
(See attached file: d.p.kennedy.vcf)



    Dr. Robert F. Dias
    Department of Chemistry and Biochemistry
    Old Dominion University
    Norfolk, VA 23529
    ph: (757) 683-4093
    fx:   (757) 683-4628
    [log in to unmask]