An 'Is this normal?' question GC-MS 5972

[mickygd]

I've been using a 5972 msd for 9 months now. (Analyzing VOC's) It has been working beautifully with great tunes etc. EM volts started out at 1253 and inched up to 1360 over 6 months.

The problem is that in the past week everytime I did a tune the EM volts jumped up 100 every 12 hours. Finally it got up to 1900. I figured it was a filament/cleaning issue. However, I couldn't trust my data anymore.

I have a lot of samples and not much time so I took the detector portion out of this machine and installed one from another 5972 that we have and that I just cleaned and replaced filaments.

I pumped down and waited 6 hrs, did a tune and got 1510 for EM volts. 10 hrs later I did a tune and got 1730. This is not behaving like I thought it would. (the detector did come from a SVOC machine, so most likely has had a harder life).

My questions:
Is this normal?
Is there something else that could be causing this jumping of EM volts (board issues)?
How to I get back to the 5972 I use to have that was very stable?

Thanks.

Mike

[Schmitty]

What temperatures do you run your source/analyzer at?

Have you changed your gas cylinder recently?

Have you changed your inline filter for the carrier (Helium?) recently?

Are there any apparent leaks that you see in your (Auto?) tune?

[mickygd]

Here are the answers to your questions:

I run MS temp at 168
I did change the helium tank just before all this happened (but I change it once per month). He supplier is one of the best in town.

The in-line filter is only 9 mo old. It's an Excelasorb brand Hydrocarbons-O2-H2O filter and is dedicated to only this machine.

[Schmitty]

Something that I've been told to do for a 5973 (I'm not sure if it's OK) is to get the temperature for the source and quads up to the max temps for a bit, to burn them off.

I'm not sure if there is a setting in Chemstation for a 5972. My remaining 5972 is at 174 righ now. This is something someone else may have some input on.

If it's not too much trouble, you might want to swap in a new cylinder/filter from a different lot that you currently are using.

Also, about your tune, what type of tune are you doing? Auto, max sensitivity...etc.? Any extraneous peaks showing up?

[Rick]

Hi!
Isolate your MSD first...cap the interface and tune instrument. In this manner, the Helium, column and contamination from GC are not present.