Ammonium dihydrogen phosphate

Hydrochloric acid, sodium hydroxide, glacial acetic acid, ferric chloride hexahydrate, ortho-phosphoric acid (≥85%), acetonitrile, sulfuric acid, L-(+)-tartaric acid, D-fructose, and 0.1 N sodium hydroxide were purchased from Fisher Scientific (Santa Clara, CA, USA). Sodium chloride, bovine serum albumin (BSA), (-)-epicatechin (≥90%), (+)-catechin (≥98%), caffeic acid (≥98%), malic acid (≥99%), and quercetin-3-glucoside (≥98%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Potassium metabisulfite (≥97%), sodium dodecyl sulfate, and ammonium dihydrogen phosphate (>98%) were purchased from Acros Organics (Geel, Belgium). Triethanolamine was purchased from Aqua Solutions, Inc. (Deer Park, TX, USA). Commercial malvidin-3-O-glucoside chloride (oenin) (≥95%) and malvidin-3,5-O-diglucoside chloride (malvin) (≥95%) were provided by Extrasynthese (Genay, France). Milli-Q water used for the preparation of solutions was obtained from a Barnstead MicroPure Water Purification System (Thermo scientific^®, Waltham, MA, USA).

Acetonitrile, D-fructose, ferric chloride hexahydrate, glacial acetic acid, hydrochloric acid, L-(+)-tartaric acid, ortho-phosphoric acid (≥85%), sodium hydroxide, sulfuric acid, and 0.1 N sodium hydroxide were purchased from Fisher Scientific (Santa Clara, CA, USA). Bovine serum albumin (BSA), caffeic acid (≥98%), (+)-catechin (≥98%), (−)-epicatechin (≥ 90%), malic acid (≥99%), quercetin-3-glucoside (≥98%), and sodium chloride were purchased from Sigma-Aldrich (St. Louis, MO, USA). Ammonium dihydrogen phosphate (>98%), potassium metabisulfite (≥97%), and sodium dodecyl sulfate were purchased from Acros Organics (Geel, Belgium). Commercial malvidin-3-O-glucoside chloride (oenin) (≥95%) and malvidin-3,5-O-diglucoside chloride (malvin) (≥95%) were provided by Extrasynthese (Genay, France). Triethanolamine was purchased from Aqua Solutions, Inc. (Deer Park, TX, USA). Milli-Q grade water (18.2 MΩ cm resistivity) used for the preparation of reagent, solutions, and high-performance liquid chromatography with diode array detector (HPLC-DAD) mobile phase was obtained from Barnstead MicroPure Water Purification System (Thermo scientific^®, Waltham, MA, USA).

For preparation of FDOPA the 6-trimethylstannyl-L-DOPA precursor was purchased from ABX (Germany). Dry chloroform >99 % for spectroscopy stabilized with amylene (stored on molecular sieves) and ammonium dihydrogen phosphate p.a. were obtained from Acros (Belgium) and 47 % hydrobromic acid, 25 % ammonia and diammonium hydrogenphosphate p.a. from Merck (Germany). A sterile solution for injection of ascorbic acid (100 mg/ml) was purchased from Centrapharm (Netherlands). A sterile 0.1 M sodium acetate solution, pH 4.7, was prepared in the hospital pharmacy. Reference compounds for calibration curves of FDOPA, L-DOPA and 6-hydroxy-DL-DOPA were purchased from respectively ABX (Germany) and Sigma Aldrich (Netherlands), HPLC supra gradient acetonitrile, used as solvent for LC-MS analysis, was obtained from Biosolve (Netherlands), ~98 % formic acid was bought from Fluka (Netherlands) and LC-MS grade water (>18.2 MΩ) was purchased from the Department of Clinical pharmacy & Pharmacology, UMCG. The reference compound leucine encephalin for calibration of the MS detector was purchased from Merck (Germany). For calibration of the MS, a solution was prepared of 200 μL 10 % formic acid, 100 μL 0.1 M sodium hydroxide (Merck, Germany) and 20 ml 80 % acetonitrile in water.