Contamination m/z 118.1230 on a LC-QTOF

Question

Hello, 
 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!

caroline_daneault · Accepted Answer

Yes, we contacted the Peak vendor this morning. We think maybe it comes from the ventilation/air who are recircutated by the nitrogen generator to the LC-QTOF.

caroline_daneault · Answer

Our mobile phase is a mix of MTBE, methanol and acetonitrile. I tested all solvant plus water separately by direct infusion via bottle B in tune mode. The 118.1230 is always present. I tested different batch of ammonium formate and old vs new bottle of solvent. I washed capillary and all part of the source that I have access. I changed column. 
 The contaminant is there since 2019 and present in our two LC-QTOF but the problem of adduct begin to be a struggle in the last month. We think that the problem came maybe from the nitrogen.