Sodium and potassium hydroxides in the form of pellets, chloroform and analytical standards (dihydrocholesterol, campesterol, stigmasterol, β-sitosterol, eicosanol, docosanol, tricosanol, tetracosanol, pentacosanol, hexacosanol, heptacosanol, octacosanol, squalene and (±)-α-tocopherol) were purchased from Sigma (St. Louis, MO, USA). Ethanol and a silylating mixture according to Sweeley were purchased from Fluka (Buchs, Switzerland).
Hydroxytyrosol, tyrosol, oleuropein, lutein and apigenin were purchased from Extrasynthese (Genay, France). Caffeic acid and gallic acid were purchased from Sigma (St. Louis, MO, USA). Standard stock solutions of each compound were 1 mg/mL in Methanol.
All mineral standards were purchased from Merck (Darmstadt, Germany) and diluted to the appropriate obtained concentration.
All standards stored at +4 °C in amber vials and in a dark place until analysis.