2.1 Materials
Samples of mixed tocopherols (7.17% α-tocopherol, 1.47% β-tocopherol, 60.04% γ-tocopherol, 24.41% δ-tocopherol, 6.98% others) were purchased from Healthful Biotechnology Co., Ltd. (Xi’an, China). Fresh refined lard (acid value 0.14 mg KOH/g, peroxide value 0.39 mmol/kg) without any antioxidants was obtained from Jiuyuan Co., Ltd. (Tianjin, China). Standards of α-tocopherol (purity > 98.0%), γ-tocopherol (purity > 98.0%) and δ-tocopherol (purity > 98.0%) were purchased from Aladdin Bio-Chem Technology Co., Ltd. (Shanghai, China). Silica gel (200-300 mesh, irregular) used for column chromatography and silica G plates (10 × 10 cm) were obtained from Haiyang Chemical Group Co., Ltd. (Qingdao, China). Quartz sand (silicon dioxide, 40-80 mesh, irregular) was purchased from Kemiou Chemical Reagent Co., Ltd. (Tianjin, China). All chemicals and solvents used were of analytical or HPLC grade.