Stock standard solutions: 225 mg of δ-tocopherol in 5 mL of ethanol with 0.025% BHT (w/v); 10 mg of ergocalciferol in 100 mL of ethanol with 0.025% BHT (w/v); 10 mg of cholecalciferol in 100 mL of ethanol with 0.025% Butylated Hydroxy Toluene(w/v); 5 mg of γ-tocopherol in 2 mL of ethanol with 0.025% Butylated Hydroxy Toluene) (w/v) and 100 mg of α-tocopherol in 2 mL of ethanol with 0.025% Butylated Hydroxy Toluene) (w/v). The solutions were stored in sealed amber vials under nitrogen N2 and in darkness at the lowest possible temperature (