Protocatchuic acid

The following standards were obtained from Sigma Chemical Co (St. Louis, MO, USA) at the highest purity available, as shown in Table 1: quinic acid, gallic acid, protocatchuic acid, catechin (+), caffeic acid, syringic acid, 1,3-di-O-caffeoyquinic acid, epicatechin, p-coumaric acid, rutin, trans-ferulic acid, hyperoside (quercetin-3-Ogalactoside), luteolin-7-O-glucoside, 3,4-di-O-caffeoyquinic acid, naringin, rosmarinic acid, 4,5-di-O-caffeoyquinic acid, quercetin (quercetin-3-O-rhamonoside), apigenin-7-O-glucoside, O-coumaric acid, Salvianolic acid, kaempferol, quercetin, trans cinnamic, silymarin, naringenin, apigenin, luteolin, cirsiliol, cirsilineol, acacetin.

Acetonitrile, ethanol, methanol, formic acid, and acetic acid were purchased from AppliChem, Panreac Quimica SA (Barcelona, Spain). Hexane, methyl tert-butyl ether (MTBE), all-E-α-carotene, all-E-β-carotene, all-E-lutein, all-E-lycopene caffeic acid, p-coumaric acid, chlorogenic acid, ferulic acid, isolariciresinol, larisiresinol, luteolin, naringenin, oleuropein, pinoresinol, protocatchuic acid, quercetin, rutin, and secoisolariciresinol were purchased from Sigma-Aldrich (St. Louis, MO, USA). Narigenin-7-O-glucoside, hydroxytyrosol, and ethyl gallate were acquired from Extrasynthese (Genay, France), vanillic acid and apigenin from Fluka (St. Louis, MO, USA), and verbascoside from HWI Analytic. C18 ODS SPE bulk sorbent was purchased from Agilent Technologies (Santa Clara, CA, USA). Ultrapure water was obtained using a Milli-Q purification system (Millipore, Bedford, MA, USA).