We profiled amino acids, biogenic amines, and other polar plasma metabolites using liquid chromatography-tandem mass spectrometry (LC-MS). Formic acid, ammonium acetate, LC-MS grade solvents, and valine-d8 were purchased from Sigma-Aldrich. We purchased the remainder of the isotopically-labeled analytical standards from Cambridge Isotope Labs, Inc. We prepared calibration curves for a subset of the profiled analytes by serial dilution in stock pooled plasma using stable isotope-labeled reference compounds (leucine-13C, 15N, isoleucine-13C6, 15N, alanine-13C, glutamic acid-13C5, 15N, taurine-13C2, trimethylamine-N-oxide-d9). We ran samples with isotope standards for calibration curves at the beginning, middle, and end of each analytical queue. We prepared plasma samples for LC-MS analyses via protein precipitation with the addition of nine volumes of 74.9:24.9:0.2 v/v/v acetonitrile/methanol/formic acid containing two additional stable isotope-labeled internal standards for valine-d8 and phenylalanine-d8. The samples were centrifuged (10 min, 10,000 rpm, 4°C) and the supernatants were injected directly. Detailed methods are provided in the Supplementary Methods.