I am getting background ions of 110.1, 154.9, and 436.3 throughout each sample acquisition, but I am mainly concerned with m/z 436.3. The mobile phases I use are 0.1% formic acid in H2O and 100% ACN. I thought the contamination was inside the mass spec because whatever I infused would give me m/z 436.3 so I cleaned the Ion Transfer tube, changed needle insert and also cleaned the skimmer cone in case any build-up was present. Afterwards, I infused my mobile phases starting with ACN and it came back clean with minimal background ions. I infused the 0.1% formic acid in H2O mobile phase and it showed m/z 436.3 like before. Then I infused straight H2O (Millipore reagent water) and it was still there so I moved to deionized water and had no luck. I even saw trace amounts of it when I infused MeOH.
Is it possible that BOTH water sources are contaminated and what exactly is m/z 436.3? I can't find it anywhere online. Is there anything else I should try or has anyone else had this kind of problem before? Also, any ideas about the other two ions present in my spectrum?