4.1. Materials
ALDRICH
Chloroform (Honeywell, Charlotte, NC, USA), methanol (Biosolve, Valkenswaard, The Netherlands), heptane (LiChorSolv, Merck, Darmstadt, Germany), UPLC-grade isopropyl alcohol (Biosolve, Valkenswaard, The Netherlands), and ethanol (Biosolve, Valkenswaard, The Netherlands) were of HPLC grade or higher. Reagent-grade potassium chloride (Sigma Aldrich, St. Louis, MO, USA) and ultrapure water from a Milli-Q Advantage A10 system (Merck, Darmstadt, Germany) were used. Synthetic ceramides and deuterated standards were purchased from Avanti Polar Lipids (Alabaster, AL, USA) or provided by Evonik (Essen, Germany).