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Stable Isotope Geochemistry

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Subject:
From:
"Chenery, Carolyn A" <[log in to unmask]>
Reply To:
Stable Isotope Geochemistry <[log in to unmask]>
Date:
Mon, 16 Feb 2004 13:29:21 -0000
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We recently replaced the filament and cleaned the source on our Delta Plus
XL continuous flow mass spec (with ConFlo III, a TC/EA and a Flash EA).
The sensitivity is now less than 1/2 of what we had before.  Previously we
had a signal on mass 45 of  5.06V for 1 bar CO2 now it is only 2.1V
During tuning I noticed the signal does not alter when the trap voltage is
changed and to get maximum intensity the X deflection, Electron energy, X
focusing voltage and Y1 are at maximum.  All the other settings are in the
middle range.
I have had the source out again and checked all the component positioning,
orientations and pin connections.  The relative intensities for mass 44, 45
and 46 are normal and peak shapes aren't bad.  The mass calibration has and
the HV DAC have not changed significantly.  The Ion gauge reading is 4.4e-6
as it always has with the needle valve open.  As far as I can tell there is
no problem with the gas inlet.
Has any one had similar problems and can you suggest the cause (and a cure).
Many thanks,
Carolyn

Carolyn A. Chenery

NERC Isotope Geoscience Laboratory
British Geological Survey
Kingsley Dunham Centre
Keyworth, Nottingham
U.K. NG12 5GG

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