Hydroxytyrosol ((3,4-dihydroxyphenyl)ethanol) was synthesized
at the Organic and Pharmaceutic Chemistry Department, Faculty of
Pharmacy (Seville, Spain). To prepare the stock standard solutions
of phenolic compounds (with concentrations ranging from 400 to
4000 mg/mL) the appropriate amount of the solid reagent was
weighed and dissolved in 25 mL of HPLC grade methanol from
Panreac (Barcelona, Spain).