Hi Pat!

Are you sure that you have set up your method so that the software is
looking for your carbon peak around the time you see the response at the
mass spec?  I've found that I usually need to be within ± 5 seconds or so,
say 240 ± 5 seconds, of the actual time of peak response, or some peaks are
never recognized.  To be really accurate (more than you really need to),
with a Carlo Erba NA 1500 NC, you can select "Raw Data" and drag the cursor
around until you find the time at which the CO2 peak reaches its maximum
value and use that number in your method file.

Unlike the versions of GC-C-IRMS software that I've used in the past, in
which you can "reanalyze" your chromatograms after making background
adjustments, etc., I've never had much luck recovering "lost" peaks after
the EA software has finished its data processing.  I would be interested to
hear if others have been more successful.

Hope this helps!

Steve


>Dear All,
>
>I contact you because of a small problem with the Data Processing of my EA.
>I've run a batch of similar samples (coal powder), after having optimised
>the method for such a material (timing, tunning of diluter a.s.o). The
>recordings are beautiful, with nitrogen and carbon peaks (on the MS)
>similar in shape, in height, and compared to reference pulse. These records
>are moreover almost identical for each sample (same material & almost the
>same weight).
>But (there is a but), at the end of the sequence, after batch DP, I found
>that on two thirds of the samples, the carbon MS peak was not recognised,
>despite it arrives at the same time and with the same amplitude for each
>sample. All nitrogen ones were recognised.
>How can I force the DP programme to find back these "ghost" peaks??
>Thanks for your help.
>
>Pat
>
>__________________________________________________________
>
>Patrick DAUBY
>Universite de Liège
>Laboratoire d'Océanologie
>Unité de Recherche en Biogéochimie des Isotopes Stables (URBIS)
>B6 Sart Tilman
>B-4000 Liège, Belgium
>Phone: +32.4.3663322  -  3663307
>Fax: +32.4.3663325
>Beep: 0454.700.671 (inside Benelux only)
>WWW: http://www.ulg.ac.be/oceanbio/urbis.htm
>__________________________________________________________

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Stephen S. Howe                         Office:  (518) 442-5053
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