All,

Short update:  Our problem has been solved... N-conf mass-scale calibration.
  Thanks for all the suggestions and especially those from F. Trensch & W.
Brand.

Bob

>At  4:03 PM 0.10.24 -0700, Robert D. Stickrod II wrote:
> >All,
> >
> >A few of us are still having trouble with what is thought to be CO2
>tailing
> >resulting in severely reduced 29/28, caused by CO at the SOURCE.  My
>carbon
> >data are not affected.  Our 29/28 has ranged between 0.03 and 0.5 for all
> >REF/sample peak pairs, except the first sample, which has a normal ratio
> >(0.7).  REF pulses of N2 sent through the Conflo have good precision and
>a
> >normal ratio if they do not immediately follow another sample through the
> >EA.
> >
> >We've changed just about everything you can change including the GC
>column
> >itself and still get depleted 29/28 when running for N & C
>simultaneously.
> >The type of samples (flour & plant material) and C/N (~7) are the same as
> >we've used for years.  The EA C/N looks fine using its TCD and Eager
> >software alone.
> >
> >Did anyone ever conclusively identify what is causing the problem?
> >Basically, the IRMS seems OK alone.  The EA seems OK as far as doing its
> >combustion job.  At some unknown point, (when the EA's get a little
>older?)
> >something changes and no one knows what it is.  We had a taste of it
> >initially back in March with 29/28 of 0.5 for one batch of samples, then
>it
> >vanished.  Now we can't figure out what the actual problem is enough to
> >eliminate it and get things back to the way they were before.  This
>mystery
> >has us at a standstill.  Any ideas would be appreciated.
> >
> >Bob
> >
> >-------------------------------------------------
> >Robert D. Stickrod II
> >Idaho Stable Isotopes Laboratory
> >Department of Forest Resources
> >College of Natural Resources, 214
> >P.O. Box 441133, University of Idaho
> >Moscow, ID 83844-1133, U.S.A.
> >[log in to unmask]
> >lab: (208) 885-6512
> >fax: (208) 885-6226
> >--------------------------------------------------
>
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