Hi Robert

If you have had a pump failure have you done a full magnet scan for the presence of hydrocarbons?
These would be coming from the oil in the pads of the turbo or perhaps the rotary pump.
You need to clean the source then bake the analyser if you have that option on your Delta V.


John Hill

-----Original Message-----
From: Stable Isotope Geochemistry [mailto:[log in to unmask]] On Behalf Of Robert van Geldern
Sent: 14 January 2013 12:22
To: [log in to unmask]
Subject: [ISOGEOCHEM] Peak Shape


we run a Delta V plus in Dual Inlet mode for CO2. We had a pre-vaccum pump failure (Pfeiffer Duo blowed themself off). After installing a new pump and new Pirani gauge standard deviations are bad (0.2 18O in a zero test). The peak shape is bad - no flat plateau in the middle cup, flanks are not very steep. The peak shape of m45 in the middle cup looks more like Gaussian chromatography peak instead.

I tried nearly every focus parameter but shape always remains that way. 
=> Any idea what parameter will influence peak shape most?

(and yes: the source is dirty...not cleaned for 2 years or so with several blown filaments due to switched off helium and the pump failure that released some oil vapor; so I suspect this is already the answer to my question...get it cleaned?)

Dr. Robert van Geldern
GeoZentrum Nordbayern / Applied Geosciences University of Erlangen-Nuremberg Schlossgarten 5
91054 Erlangen, Germany

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