2.8. Chemicals
The fatty acid methyl ester mixture used for the relative retention time index and the authentic standards used for the identification of significant metabolic markers were purchased from Sigma-Aldrich (St. Louis, MO, USA). Extraction solvents used for sample preparation, such as isopropanol, acetonitrile, and water (HPLC grade), were obtained from J.T. Baker Chemical Co. (Phillipsburg, NJ, USA). Pyridine, methoxamine hydrochloride (MeOX), and N-methyl-N-(trimethylsilyl) trifluoroacetamide were used for derivatization and purchased from Sigma-Aldrich. The Biocrates