Metabolomic Analysis of Aromatic Compounds

HPLC-grade solvents dichloromethane, n-pentane, and methanol, LC–MS-grade methanol, acetonitrile, 2-propanol, chloroform, formic acid, ammonium formate, ethyl heptanoate, 1-heptanol, 2-octanol, ethyl hexanoate-d11, 3-(2-hydroxy ethyl)-indole, kynurenic acid, d-tryptophan methyl ester, L-tyrosine-ethyl ester, N-acetyl tyrosine-ethyl ester, and 3,5-di-tert-4-butylhydroxytoluene (BHT) were obtained from Sigma-Aldrich (St. Louis, MO, USA). C7–C30 n-alkane solution in n-hexane was purchased from Supelco (Bellefonte, PA, USA), while cholesterol-d7 and octadecanoic acid-d3 were obtained from CDN Isotopes (Quebec, QC, Canada). The chemical standards used to determine aromatic amino acid metabolites and lipid molecules were purchased from Aldrich-Fluka-Sigma S.r.L. (Milan, Italy), except for tryptophol-2-sulfonate (Tol-SO3H), indole-lactic acid-2-sulfonate (Ila-SO3H), and indole-acetic acid-2-sulfonate (IAA-SO3H) that were synthesized as described [26 (link)].