Analytical Standards for Metabolomics

Reagent grade potassium carbonate (K₂CO₃), potassium bicarbonate (KHCO₃), sodium hydroxide (NaOH) and hydrochloric acid (HCl) were obtained from Sigma-Aldrich (Steinheim, Germany). Analytical grade formic acid (HCOOH) and LC-MS grade isopropanol (IPA), acetonitrile (ACN) and water (H₂O) were purchased from Fisher Scientific (Fairlawn, NJ, USA). LC-MS grade methanol (MeOH) was purchased from Honeywell International Inc. (Morristown, NJ, USA). HPLC grade dichloromethane (DCM), anhydrous ACN, and 6-aminoquinoline-N-hydroxysuccinimidyl carbamate (AQC) for derivatization of amino acids were purchased from Santa Cruz Biotechnology, Inc. (SCB, Dallas, TX, USA). Amino acids, bile acids and the other analytes were obtained from Sigma-Aldrich, SCB or Cambridge Isotope Laboratories Inc. (CIL, Tewksbury, MA, USA), as listed in [16 (link)]. bile acids lithocholic acid (LCA), glycolithocholic acid (GLCA) and ursodeoxycholic acid (UDCA) were obtained from CIL.