The lipid reference standard mixture was purchased from Avanti Polar Lipids (Differential Ion Mobility System System Suitability Lipidomix, Alabaster, AL). Trifluoracetic acid (TFA), acetonitrile (ACN), and 1.0 M NaOH were purchased from Fisher Scientific (Hampton, NH). acetonitrile/aqueous sodium trifluoroacetic acid solution (1:1 ACN/0.1% TFA, pH 3.5) was prepared according to Moini et al.20 (link) Pierce negative ion calibration solution (Calmix) was purchased from Thermo Scientific (Rockford, IL). Lipids were extracted from HAP1 and yeast cells using a CHCl3/MeOH/H2O (6:3:2, v/v/v) solvent system, an aliquot of the organic layer was dried under vacuum, and the dried lipid material resuspended in ACN/IPA/H2O (65:30:5, v/v/v). For mouse cecum and plasma samples, lipids were extracted using an MTBE/MeOH/H2O (10:3:2.5, v/v/v) solvent system, an aliquot of the organic layer was dried under vacuum, and the dry lipid material resuspend in MeOH/toluene (9:1). Further sample preparation details are provided in Supplemental Methods.