Methanol (HPLC grade), ammonia solution (25%), and water (LC–MS grade) manufactured from Merck KGaA (Darmstadt, Germany) and ammonium formate, formic acid, and sulfuric acid (H2SO4, 98%) purchased from sigma-aldrich (MO, USA) were used. Two kinds of herbal medicines, Farfarae Flos an...
MEQ (purity > 98%) was purchased from A Chemtek, Inc. (Woburn, MA, USA). Sea cucumber samples were purchased from the local market. Acetonitrile, Methanol, formic acid, and ethyl acetate (HPLC grade) were purchased from Dima Technology Inc. (Muskegon, MI, USA). Metaphosphoric acid (ana...