Stock standard solutions: 225 mg of d-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% BHT (w/v); 5 mg of c-tocopherol in 2 mL of ethanol with 0.025% BHT (w/v) and 100 mg of a-tocopherol in 2 mL of ethanol with 0.025% BHT (w/v). The solutions were stored in sealed amber vials under nitrogen N2 and in darkness at the lowest possible temperature (-20 C). The solutions were stable for 3 months at -20 C.