Have you tried using a different oxygen loop ie instead of micro try 
semi-micro or macro.  Also maybe run an Ar check on the He regulator on the 
EA.  Good luck.
Shapna
Water and Aquatic Sciences Research Program
University of Victoria, Department of Biology
PO Box 3020, Station CSC,
Victoria, BC, Canada V8W 3N5
(250) 472-4789
----- Original Message ----- 
From: "Bjoern Wissel" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, February 20, 2008 1:14 PM
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
>