5975C PCI sensitivity issues

[bcanney]

I'm having some sensitivity issues with my new Agilent 5975C. I'm wondering if anyone else has seen a similar problem or can suggest a solution. I have an increase in the noise which is drowning out my analyte in methane CI. I've capped off the MS and this is what I can see:
-There is a constant pattern to the noise from 57 to ~200 amu spaced 12-14 m/z apart and decreasing in size as the mass gets larger. Abundance of m/z57 is ~10,000 counts and m/z 200 ~500 counts.
-When I switch to EI mode (with EI source) everything appears to function normally.
-I have compared the PCI tunes to those in the past and what I can see is that the EIEnergy is dropping. It originally started out around 200 was constant for a while then dropped to ~135. Again remained constant and dropped a third time to ~77. Each drop I notice a loss of sensitivity.

Tried so far:
-Cleaned ion source
-New filament
-New HED and EM
-New methane filter and new methane from different supplier
-Cleaned transfer line and tubing
-Cleaned Quad (Agilent service)
-Changed PFDTD (Agilent service)
-Changed CI flow controller and lines (Agilent service)

Most recent tune report: Emission: 202.7, EIEnergy: 77.3, Repeller: 1.64, IonFocus: 125.3, EntLens: 15.0, EMVolts: 1106

Thanks,
Brad

[tlahren]

DISCLAIMER: I am fairly new to running CI.

That's funny. I just had my entire flow controller assembly replaced as well under warranty.

After this it still wasn't functioning the way I had expected so I called Agilent back. Every Agilent rep told me that there are really no specifics values that one can expect during a CI tune. Basically if it completes the Autotune procedure then everything should be OK. If somethings wrong it will stop. I was seeing the last two tune peaks (from the PFDTD) dropping in abundance by almost 10 fold while watching in manual tune profile view. Agilent told me that this is probably due to the filament wire sagging (CI wire is longer than EI wire I think). They said to just start the tune view and click Autotune and let it go.

I have to say for the largest part of all my problems they were right. I tried analyzing standards using multiple tunes, which I would say were WAY different from each other, but my spectra and chromatograms were almost identical in every case.

The values you listed don't seem abnormal to me considering I saw the same things you did (large fluctuations between tunes).

If during the Autotune the EIEnergy is dropping, why not manually set it to 200 after an Autotune and then save the Tune File? Then run a standard and see if your sensitivity is back.

Also, let the instrument sit for a few hours (maybe overnight) after your tuning procedure. Then come back and try and run without re-tuning. This is to test the filament sagging issue. Mine seemed to come back after a few hours of being off but standard analysis didn't seem to cause any negative effects. It was just during the tuning or if I tuned too many times.