Hi Bjoern,

Maybe there is a restriction lurking somewhere.  Did you go through all
the lines in the EA when you were checking the plumbing?  A reactor tube
or trap packed too tight could also cause restriction.  Has your He flow
rate decreased?  Do you see the peak delay with the TCD as well?  

Hope this helps, 

Benjamin Harlow
Washington State University



-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On
Behalf Of Bjoern Wissel
Sent: Wednesday, February 20, 2008 1:14 PM
To: [log in to unmask]
Subject: [ISOGEOCHEM] update on delayed peaks

Hi there,
last week I sent out a message asking for advice in respect to an
elevated N2-
baseline (40 mV instead of 15 to 20 mV) and delayed peaks running basic
C+N 
samples on a Costech EA connected to a Finnigan DElta plus.
Unfortunately, neither baking out the column or changing it for a brand
new 
one didn't help. At this point I have changed pretty much all components

including autosampler, columns, traps, seals, plumbing etc.. I also did
several 
extensive leak checks using the EA pressure valve, a He detector and Ar
gas 
(without finding any leaks). Yet, my feeling is that only a pretty large
leak 
would be able to delay the N2 peak by 100 sec (from the usual 100 to 200

sec). 
My second thought was that something might block the flow and this way 
delays the peak, but since I have exchanged pretty much all components I

don't know what could block the flow.
If I increase the pressure to about 220, everything looks normal but it
doesn't 
seem the right solution to this problem. 
I anyone has some additional thoughts or crazy ideas, please let me
know!
Thanks, Bjoern