Bjoern- Check the status of the mass flow controller in your EA. We had 
a similar problem, the flow was reduced (for no apparent reason at 
first) and eventually we traced it to the He mass flow controller, which 
had come on and was restricting the flow rate. A reduced flow rate will 
cause both the N2 peak shift and inreasing baseline problems. -Jay Brandes

Toti Larson wrote:
> If the oxygen is the problem (source of N2 and maybe flow rate issue) 
> can you turn the O2 off completely to see how things behave?
> I feel your pain...we were trouble shooting N2 on an EA for a long 
> long time and eventually isolated the problem to an intermittent leak 
> on our autosampler. Sometimes it passed the leak test, and othertimes 
> it did not.
>
> Bjoern Wissel wrote:
>> 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
>
> Toti Larson, Ph.D.
> Los Alamos National Laboratory
> Earth and Environmental Sciences Division
> Hydrology, Geochemistry and Geology Group
> MS-D469. Los Alamos, NM 87545
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> Office: (505) 667-1110
> Lab:    (505) 667-9894
> Fax:    (505) 665-3285