Chromatography Forum

Good afternoon everyone!

I am a beginner in GC / MSMS. I'm having trouble finding my analytes in full scan. All the peaks that appear do not match with NIST, and I'm using 70 eV on the ion source.

Thank you

debora.ferreira wrote:
Good afternoon everyone!

I am a beginner in GC / MSMS. I'm having trouble finding my analytes in full scan. All the peaks that appear do not match with NIST, and I'm using 70 eV on the ion source.

Thank you

Are you operating in single quad mode to collect the spectra?

What instrument and software are you using?

Do you have good signal to noise ratios for the analytes peaks, much higher than 10:1?

I use an Agilent device, the software is MassHunter. The GC model is 7890B and the MS / MS is 7010B.
To collect the full scan spectra I select the single mode on quad 2 (factory recommendation). And yes, I have a good signal to noise ratio, but the peaks do not match with NIST.

James_Ball wrote:

debora.ferreira wrote:
Good afternoon everyone!

I am a beginner in GC / MSMS. I'm having trouble finding my analytes in full scan. All the peaks that appear do not match with NIST, and I'm using 70 eV on the ion source.

Thank you

Are you operating in single quad mode to collect the spectra?

What instrument and software are you using?

Do you have good signal to noise ratios for the analytes peaks, much higher than 10:1?

debora.ferreira wrote:
I use an Agilent device, the software is MassHunter. The GC model is 7890B and the MS / MS is 7010B.
To collect the full scan spectra I select the single mode on quad 2 (factory recommendation). And yes, I have a good signal to noise ratio, but the peaks do not match with NIST.

James_Ball wrote:

debora.ferreira wrote:
Good afternoon everyone!

I am a beginner in GC / MSMS. I'm having trouble finding my analytes in full scan. All the peaks that appear do not match with NIST, and I'm using 70 eV on the ion source.

Thank you

Are you operating in single quad mode to collect the spectra?

What instrument and software are you using?

Do you have good signal to noise ratios for the analytes peaks, much higher than 10:1?

We use the Agilent 7000C and for single quad we use quad 1 (the option for quad 2 alone is not in our version of Mass Hunter) with no collision or quench gas.

It could be the mass balance of the tune that can cause library searches to not match up. EPA uses a check versus DFTPP(Decafluorotriphenylphosphene) to make sure the tune of the instrument will give mass abundances that will match up to those in reference libraries. For MS/MS work the tune will be for maximum sensitivity in the mass range of the target analyte, but may not be optimum for matching the NIST or Wiley library.

Are the peaks at the correct mass? i.e. is the instrument calibrated correctly?

I finally got it. I called Agilent and the problem was the backgroung that was too loud. I had to leave the column in bakeout for 24 hours. And then it worked.

PS: The recommendation was to let the collision cell gases on!

Thank you all!