On Mon, 16 Feb 2004, Chenery, Carolyn A wrote:

> 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
>

Carolyn,

some time ago we had a similar problem. The reason was that the filament
(the wire itself, not the complete kathode) wasn't mounted in centre.
Subtle deviations may cause severe problems here. Use a magnifying glass
and carefully have a look at the filament.

--
        Uli Flenker

        Institute of Biochemistry
        German Sport University Cologne
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