First signal GC-MS

[ellis]

Hello,

I have a question about a signal that apperars always into my chromatograms obtained from GC-TOF analysis. The problem is particulary importan into diluited samples.
I have a GC-TOF and, during my air analysis, I observed a peak into the chromatogram, characterized by a m/z signal of 44. I don't see lower m/z due to the mass setting.
I have tried to set a solvent delay in order to cut off this signal (firstly I thought that it could be a solvent signal), but it is always present. In diluited samples, this peak is very important, but I can't remove it.
Is it possibile that, after the solvent delay, the source turns on and that peak is due to an electrical signal I detect?

Thanks a lot for your help!

[James_Ball]

Hello,

I have a question about a signal that apperars always into my chromatograms obtained from GC-TOF analysis. The problem is particulary importan into diluited samples.
I have a GC-TOF and, during my air analysis, I observed a peak into the chromatogram, characterized by a m/z signal of 44. I don't see lower m/z due to the mass setting.
I have tried to set a solvent delay in order to cut off this signal (firstly I thought that it could be a solvent signal), but it is always present. In diluited samples, this peak is very important, but I can't remove it.
Is it possibile that, after the solvent delay, the source turns on and that peak is due to an electrical signal I detect?

Thanks a lot for your help!

Often m/z 44 is due to CO2 being present. If you see a large peak of it just as the filament turns on, then some CO2 is being adsorbed onto the filament or source parts and flashes off once the filament comes on. If it is a constant in the background then you are just seeing CO2 contamination in the carrier gas either from the tank itself or a small leak somewhere in the system.

I have also seen it in the column bleed from a few types of stationary phases, but not too often and always at high temperatures.

[ellis]

Thank you for your clarification. In my chromatograms, I see a large peak with MS spectrum of 44 m/z when the filament turns on.
From your experience, is it possible to eliminate this peak?
Thanks in advance

[James_Ball]

At the beginning of the day you can manually turn on the filament in manual tune and let it run for a few minutes to clear out any accumulated CO2 or column bleed, which usually makes the peak smaller if it is normally largest on the first run of the day.

All of my chromatogram have at least a small peak that appears when the filaments first turn on, my scan range starts at 35m/z and up to 500m/z, mostly it is masses from air and solvent. A good rule is to turn the filament on at least 30 seconds before the first expected target peak so it can burn off anything that has accumulated on the filament between runs and become stable in its output.

Another possibility is the ferrule on the MS column interface has shrank a little due to the heating cycles of the oven. It can become just loose enough that at the lowest temperature of the run it leaks a little air but seals once the temperature ramp begins. You might just need to give the nut an additional 1/8 to 1/4 turn to reseal it.

[ellis]

At the beginning of the day you can manually turn on the filament in manual tune and let it run for a few minutes to clear out any accumulated CO2 or column bleed, which usually makes the peak smaller if it is normally largest on the first run of the day.

All of my chromatogram have at least a small peak that appears when the filaments first turn on, my scan range starts at 35m/z and up to 500m/z, mostly it is masses from air and solvent. A good rule is to turn the filament on at least 30 seconds before the first expected target peak so it can burn off anything that has accumulated on the filament between runs and become stable in its output.

Another possibility is the ferrule on the MS column interface has shrank a little due to the heating cycles of the oven. It can become just loose enough that at the lowest temperature of the run it leaks a little air but seals once the temperature ramp begins. You might just need to give the nut an additional 1/8 to 1/4 turn to reseal it.

Thank you so much for your help! I will try these tips in order to reduce this problem.