The system was operated isocratically at a flow rate of 1.2 mL/min. The identification of tocopherols
(แอลฟา, เบต้า,แรมด้า and เดวต้า-tocopherol) was conducted by comparing the HPLC retention time with those of standard compounds (Supelco, Bellefonte, USA) under the same operating conditions and the quantification was based on an external standard method.