Cell samples were prepared, treated and harvested as described in supplementals (document S1). The sample processing was conducted in two steps, as described in supplementals. Briefly, after a polar metabolite extraction using methanol:water solution (4:1, v/v), lipids were extracted from the remaining pellet with 100% isopropanol. Shortly before analysis, the dried lipid samples were reconstituted in 120 µL of methanol and shaken for 15 min at 1200 rpm/4 °C. Prior to the transfer to Waters Total Recovery glass vials (Milford, MA, USA), the samples were centrifuged for 15 min at 14000g and 4 °C. Pooled quality control sample was created by aliquoting 20 μL of each sample with subsequent thorough mixing. For the evaluation of µF/mnESI ionization, dynamic range and adduction patterns, the Ultimate SPLASH ONE mix of 69 deuterated lipids was diluted 50-, 500-, 5'000-, 50'000-and 500'000-fold with methanol. For resulting concentrations see supplementary Table .