Acetonitrile HPLC grade (assay 99.9%) was purchased from Panreac Química S.A. (Barcelona, Spain); trifluoroacetic acid for HPLC (assay 99%) and formic acid for HPLC (assay 98%) were purchased from Sigma–Aldrich (Madrid, Spain). Folin–Ciocalteu reagent was purchased from Merck (Darmstadt, Germany). Water was purified by a Milli-Q water purification system from Millipore (Bedford, MA, USA).
The β-carotene and lutein standards used in this study was purchased from the Sigma Chemical Company (St. Louis, MO, USA). Other reagents including methanol, chloroform, n-hexane, petroleum ether (PE), diethyl ether (DE), acetone, ethanol, sodium chloride, potassium hydroxide, tri-ethyl amine and butylated hydroxyltoluene (BHT) were of analytical or HPLC grade.
The β-carotene and lutein standards used in this study was purchased from the Sigma Chemical Company (St. Louis, MO, USA). Other reagents including methanol, chloroform, n-hexane, petroleum ether (PE), diethyl ether (DE), acetone, ethanol, sodium chloride, potassium hydroxide, tri-ethyl amine and butylated hydroxyltoluene (BHT) were of analytical or HPLC grade.