Chromatography Forum

I am having problems with 'grass' type noise in samples run after a recent MSD clean. Noise is throught the 10 min run but seems worse as temp ramps up.
Note EM horn is getting to the end of it's life EM volts 2800
-First assumption was contamination so re-cleaned source.
checked all connections - blue entrance lens wire seems a bit loose at the pin.
-Tune is perfect with background peaks 178, ent lens & ion focus consistent with previous tunes. EM voltage 2600. so passes all checks.
-tried switching filaments -no difference to sample background
-trimmed inlet end of column.
-venting at the moment to reseat MS end of column.

Could it be column related as MS tunes seem ok? or is it a loose connection at the entrance lens?Tried the lens ramping but can't find a diagram anywhere in the help menu as to what they should look like.

Any ideas?

I am having problems with 'grass' type noise in samples run after a recent MSD clean. Noise is throught the 10 min run but seems worse as temp ramps up.
Note EM horn is getting to the end of it's life EM volts 2800
-First assumption was contamination so re-cleaned source.
checked all connections - blue entrance lens wire seems a bit loose at the pin.
-Tune is perfect with background peaks 178, ent lens & ion focus consistent with previous tunes. EM voltage 2600. so passes all checks.
-tried switching filaments -no difference to sample background
-trimmed inlet end of column.
-venting at the moment to reseat MS end of column.

Could it be column related as MS tunes seem ok? or is it a loose connection at the entrance lens?Tried the lens ramping but can't find a diagram anywhere in the help menu as to what they should look like.

Any ideas?

The ramps should be smooth not jagged. I will ramp the one on our instrument later to see what it looks like and see if I can get a screen capture of it, but I believe it jumps in the first half volt then slowly drops, but I could be backwards on that.

At that EMV you may have to increase your Threshold setting to eliminate most of the grass. Is it noise across the entire scanning range? Column bleed will start out with m/z 207 for most columns of the polysiloxane type with other masses coming in more as the temp increases.

What do you have the threshold set to in the method?

What type of sample introduction are you using?

Thanks for reply, as it turned out replacing EM Horn fixed the problem. Agilent also checked HED output and it was working fine. What puzzled me was that the tune was really good with backgrounds of only 200 + , all my experience seemed to say the tune should have been a lot worse for the EM horn to be completely dead. And yes the noise was over the entire scan range.
So I will have to file this away to experience !!!
Thanks again.