Contamination m/z 118.1230 on a LC-QTOF


Is anyone had struggle with the m/z 118.1230 as a contaminant, in positive ionisation mode on a LC-QTOF?

We do lipidomic and it create a lot of problems on lipids which ionise as an [M+NH4]+ as phosphatidylinositols, cholesteryl esters and triglycerids.

Do you have any idea where it could come from? How we can reduce or eliminate the signal?

Thank you in advance!

Parents Reply
  • You are probably right about the nitrogen. 118.12 can be a contaminant linked to hydrocarbon impurities in Nitrogen. Sometimes it can be seen to build up overtime in tune mix (the bottles are under nitrogen on the instrument). In which case it can interfere with the 1180.863 tune ions. I assume you nitrogen is coming from a nitrogen generator. You could approach your Nitrogen generator vendor / service provider about additional traps for this and see if they thing something like an active carbon trap would work (For example, this product from PEAK Peak's Resource Portal ( The generators extract nitrogen from the air but don't necessarily have the capability to remove these impurities.

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