No peak in negative

[alcorn]

..

[sav]

Hi all
I can't tune my agilent 6410 LC-MS in negative mode. Due to missing low mass fragments, Autotune is not completed and I must use manual tune instead.

Try to clean or replace resistive glass capillary (transfer optics).

[alcorn]

Thanks. I replaced the capillary and cleaned other parts, but it did'nt help me.

[sav]

Thanks. I replaced the capillary and cleaned other parts, but it did'nt help me.

May be you have shifted mass scale in -ESI (unappropriate default MS parameters).

Hypothesis: 108.7 = 112.99; 416.10 = 431.98; 579.5 = 601.98

Try to replace 301.99 to 431.98 and increase window from 16 to 48.

Also, the intensity of 118 and 322 ions is relatively low (+ESI), so try to optimize ion source parameters (decrease dry temp, etc.) and replace calibration solution.

[pepterpol]

Hello,

When you switch from positive to negative mode with calibration flow on do you see signal for target negative ions decreasing rapidly?

Did you check MS2Scan?

Did you load some old autotune file?

[alcorn]

Thanks.
Actually mass parameters (i.e drying gas temperature) were not altered after last good autotune. As can be seen in the linekd pictures, the base problem is low fragment missing or their low intensity ,and that is why autotune could not be completed.

Answer to the questioned:
- Calibrant is new

- When I changed positive mode to negative, peak intensities are decreased rapidly (for standard calibrant solution).

- Last successfully passed autotune was used, but it didn't changed situation.

- I didn't use MS2Scan. How can it help?

[Rndirk]

- I didn't use MS2Scan. How can it help?

MS1 and MS2 scan should give the same results. If you do see the peaks in MS2 and not in MS1, the problem lies with your first quadrupole.

[alcorn]

Today I checked MS2 scan but the same results were obtained.

[pepterpol]

Hello again

It may sound like a silly question but its good to check even obvious things.
ESI-L Tuning Mix (G1969-85000) and the APCI-L (G1969-85010) have the same positive ions but differ in negative. You are sure that you use the proper tuning mix.

Could you clarify the increase of peak intensities when switching polarization mode from positive to negative? You see the proper masses (neg) for few seconds and they rapidly decreases to almost zero abundance? We have such symptom year ago and cleaning of optics helps.

[alcorn]

Thanks Pepterpol

My tuning mix is correct, since about 2 years I'm using it and there was no problem about negative mode previously. My current problem (low intensity for low mass fragments in +ESI and no peak in -ESI) has occurred two weeks ago, after bad pollution of the mass spectrometer.

I apologies for my previous post, I had a mistake: When I changed positive mode to negative, peak intensities are decreased rapidly (for standard calibrant solution).

[pepterpol]

Hello
If you check/clean all easily accessible parts on the calibrant way and there is no improvement i think you should dig deeply...skimmer/octopole cleaning.

There was similar problem discussed on researchgate lots of useful inforamtion:
https://www.researchgate.net/post/Is_it ... ative_mode

Good luck