Chromatography Forum

Hello,

Our Thermo LTQ will not tune due to the mass of cal mix bouncing around as shown:
https://drive.google.com/file/d/1wsMEuq ... sp=sharing

The cal mix consists of caffeine, MRFA and Ultramark 1621. We have all green diagnostics and readbacks. I have even tried a different source from an instrument I know is working, and we observe the same. The instrument will pass the multipole and main RF calibrations.

Our settings were taken from the manual detailing the initial tuning:
Positive polarity
Spray voltage: 4.50 kV (though I have gone to the max with no change)
Aux and sweep gaes: 0
Sheath gas: 10
Capillary temp: 275 (I've gone to 350)
Capillary voltage: 13 (I've gone to 35)
Tube Lens Offset: 100 (I've gone across the entire range of +/- 140)
Max injection time: 200 ms (I tried the max of 8000 ms)
Our conversion dynode reads -15kV and both multiplers are at -1200 (I've ramped them to -2500 with no change)

Changing between +/- polarities shows the same results.

I even cleaned the multipliers following this document from Agilent and did see an increase in intensity: https://community.agilent.com/technical ... /files/654

It feels like it's something electrical but I'm not sure what it could be. At this point, I'm trying to find someone we could pay to send our top cover and coil box to as that's all I can think of. I've looked at the trap wiring based on the manual and it looks correct.

Any help/feedback would be greatly appreciated!

Since you have the same phenomenon in both + ve and
- ve ion modes, I wonder if an instantaneous interruption of the solution flow (with resultant m/z bounce) may be caused by a particle in the capillary line.

Has there been any increase in back pressure?

Have you cleaned/changed the capillaries?

Regards,

JMB

Since you have the same phenomenon in both + ve and
- ve ion modes, I wonder if an instantaneous interruption of the solution flow (with resultant m/z bounce) may be caused by a particle in the capillary line.

Has there been any increase in back pressure?

Have you cleaned/changed the capillaries?

Regards,

JMB

That's a good point! In a roundabout way I have - I switched from our ESI to HESI source from our working QQQ and observed the same thing.

The more I think about this issue the more I think that either ions aren't making it to the trap, or they aren't being trapped correctly. So, I sent the entire ion optic assembly (below) to a contact I have to be tested. If he finds that to work on his system, I'm going to send him our actual trap, then source PCB, then entrance optics then our coil box last. I've never seen a mass spec do this.
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I should have asked this in my first reply, but I'll ask now.

Can you post a TIC and individual mass chromatograms for all of the mass calibration ions?

This may indicate whether the signal in different channels drops out randomly or whether ALL signals collapse at the same time.

Regards,

Motoball

I should have asked this in my first reply, but I'll ask now.

Can you post a TIC and individual mass chromatograms for all of the mass calibration ions?

This may indicate whether the signal in different channels drops out randomly or whether ALL signals collapse at the same time.

Regards,

Motoball

I apologize for the delay as I had sent some parts out for assessment and repair. I cannot post what you requested as there is nothing ever shown on the screen other than this:
https://drive.google.com/file/d/1wsMEuq ... sp=sharing

Our ion optics assembly was returned to us and found to be in good work order, so it's something particular to our instrument.