Dear Isotopers,

recently I discovered that the zero enrichment tests (same gas on sample and 
standard sides - by definition should give delta values of 0) I run routinely 
on my 10 year old Finnigan MAT 251, do not yield the desired results. Delta 
45/44 is all right, giving ±0.0xx per mil. Delta 46/44, however, runs at 
0.2xx (mostly positive). All this began after a series of power failures in 
our lab, which flooded the instrument with air (up to three times a week).

As I could figure out as yet, the most likely culprits are the inlet 
capillaries; when I heat them up, they start outgassing, visible mostly on 
mass 44 with different intensities on sample and standard side.

My question: Can these capillaries build up some sort of a "memory effect" 
which would explain the situation and what could be the solution? - Exchange 
the capillaries? Bake them out?

I would appreciate any advice, suggestion etc. which may help to sort out 
this problem.

Kind regards, 

Uwe

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Dr. Uwe E. Horstmann
Council for Geoscience - Geological Survey
P/Bag X112
0001 Pretoria
South Africa

Tel.: +27/12 841 1361
Fax.: +27/12 841 1278
e-mail: [log in to unmask]
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