Pyrogallic acid

Lutein (xanthophyll from marigold), zeaxanthin, α- and β-carotene, β-criptoxanthin and phytoene, tocopheryl acetate, trimethylamine, celite, potassium hydroxide (KOH) and sodium chloride (NaCl) were obtained from Sigma Aldrich (Madrid, Spain). Anhydrous sodium sulfate and pyrogallic acid were supplied by Panreac (Barcelona, Spain). Methyl tert-butyl ether (MTBE), methanol (MeOH), ethanol, dichloromethane, petroleum ether and diethyl ether, were obtained from Análisis Vínicos (Spain). MeOH and MTBE were High-Performance Liquid Chromatographic (HPLC) grade.

Fluorescein sodium salt (purity ≥ 97%); 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AAPH, purity ≥ 97%); 5,5-dithiobis(2-nitrobenzoic acid) (DTNB, purity ≥ 98%); quercetin (purity ≥ 95%); iron (III) chloride hexahydrate (purity ≥ 99%); acetonitrile (for HPLC, gradient grade, ≥99.9%); hexane (for HPLC, ≥97.0%,GC); gallic acid (purity ≥ 97%); and tetramethylchromane-2-carboxylic acid (Trolox, purity ≥ 97%) were purchased from Sigma-Aldrich (USA). Di-potassium hydrogen phosphate anhydrous (purity ≥ 98%); potassium di-hydrogen phosphate (purity ≥ 98%); sodium acetate anhydrous (purity ≥ 99%); trichloroacetic acid (TCA; purity ≥ 99%); thiobarbituric acid (purity ≥ 98%); 1-butanol (purity ≥ 99.5%); pyrogallic acid (purity ≥ 99%); hydrogen peroxide (H2O2, purity ≥ 33%); sodium carbonate (purity ≥ 99.5%); Folin-Ciocalteu reagent; and hydrochloric acid (HCl; 37%) were purchased from PanReac AppliChem (Germany). Acetic acid (purity ≥ 99.8%); ortho-phosphoric acid (purity ≥ 85%) was purchased from Component-Reaktiv (Russia). 2,4,4-Tris(2-pyridyl)-1,3,5-triazine (TPTZ, purity ≥ 99%) was purchased from Acros Organics (China).