FLAT line in the TIC

[Prim]

Hello everyone,

I was wondering if anyone could point me in the right direction. I have a Waters Acquity and Quattro system, I normally run in MRM. However, when running a ms scan or daughter ion scan I have a flat line in the TIC at 100% - I have ions in the mass spectrum, but no chromatography.

Any help/thoughts/idea would be much appreciated



Thanks

Prim

[thohry]

You cannot see a peak because the sensitivity of MRM is hundreds times higher than in MS-Scan. Samples run in MRM do not appear in Scan mode.

[Alp]

It might not be the right word,... chromatography, I think better to describe it as baseline noise. In any case, I would expect noise to be higher if you were doing an ms scan.
MRM (ms/ms) will give you LESS noise, or more acurrately, higher signal to noise.

Why you are seeing no noise during ms scan? Sorry I am not familiar with Aquity or Quattro so I can only throw guesses at you.
Perhaps your parameters are not optimal for MS scan. Like source voltage, declustering potential, entrance voltage, ring or orifice parameters?
Do you have a "threshold cut off" setting?
Detector voltage?

[Prim]

Thanks both...

In any case, I would expect noise to be higher if you were doing an ms scan.
MRM (ms/ms) will give you LESS noise, or more acurrately, higher signal to noise.

Agreed.

The problem was that someone had changed the display options After re-boot from telnet and checking the comns were ok, I went a searching. Turns out the data wasn't being normalised to the largest peak...some crazy value had been added! So all data was below the threshold.

Thanks for the replies