4 hydroxyglucobrassicin

Chemicals and reagents were obtained from the following commercial sources (purity in parenthesis): Gluconapin (3but) (84%), glucoerucin (4mtb) (90%), glucobrassicin (I3M) (86%), glucoraphanin (4msb) (89%), glucoiberin (3msp) (98%) and internal standard, sinalbin (99%) were purchased from PhytoLab GmbH & Co. KG (Vestenbergsgreuth, Germany). 4-Hydroxyglucobrassicin (4OHI3M) (95%), 4-methoxyglucobrassicin (4MOI3M) (94%) and neoglucobrassicin (NMOI3M) (97%) were acquired from Phytoplan, Diehm & Neuberger GmbH (Heidelberg, Germany). Acetonitrile and methanol (LC/MS grade solvents) were obtained from Fisher Chemical (Roskilde, Denmark). Water was obtained from a MilliQ purifier (Millipore, MA, USA). Glacial acetic acid was purchased from Merck (Darmstadt, Germany).

For headspace solid-phase-microextraction (HS-SPME), calcium chloride and the alkane standards C₆-C₂₅ (100 μg/mL) in diethyl ether were obtained from Sigma-Aldrich (now Merck; Poole, UK). For ultra-high performance liquid chromatography mass spectrometry (UPLC-MS), authentic compounds of glucoiberin (GIB; 99.61%, HPLC), progoitrin (PRO; 99.07%, HPLC), sinigrin (SIN; 99%, HPLC), glucoraphanin (GRA; 99.86%, HPLC), glucoalyssin (GAL, 98.8%, HPLC), gluconapin (GNP, 98.66%, HPLC), 4-hydroxyglucobrassicin (4HGB; 96.19%, HPLC), glucobrassicanapin (GBN; 99.22%, HPLC), glucotropaeolin (GTP; 99.61%, HPLC), glucoerucin (GER; 99.68%, HPLC), glucobrassicin (GBR; 99.38%, HPLC), and gluconasturtiin (GNT; 98.38%, HPLC) were purchased from PhytoPlan (Heidelberg, Germany). Methanol (HPLC grade), formic acid (LC-MS grade), and acetonitrile (LC-MS grade) were purchased from VWR (Leicestershire, UK).

The cherry radishes (Raphanus sativus L. var. radculus pers) were purchased from a commercial market, Guoxiangsiyi (Beijing, China). The 4-hydroxyglucobrassicin was purchased from PhytoPlan (Heidelberg, Germany). The methanol was purchased from Thermo Fisher Scientific (China) Co., Ltd. (Shanghai, China). The trifluoroacetic acid (TFA) was purchased from Sigma-Aldrich (St. Louis, MO, USA). The ASA was purchased from Biotopped (Beijing, China). Additionally, the ammonium molybdate was purchased from AI Qaeda chemical plant (Tianjin, China). Other chemicals were obtained from Beijing Chemical Plant (Beijing, China).