Development of an HPLC/diode-array/fluorimetric detector method for monitoring tocopherols and tocotrienols in edible oils

This paper describes an HPLC procedure for the determination of tocopherols and tocotrienols in crude and edible vegetable oils. The sample preparatio n only involves a dissolution of the oil in n-hexane and filtration. The ch romatographic separation was achieved using a normal phase column LiChrosor b SI 60 (5 mum; 25.0 x 0.4 cm). Isocratic elution was carried out using n-h exane :2-propanol (99.7:0.3). The effluent was monitored by using diode-arr ay and fluorimetric detectors. The determinations were performed in the following linear ranges: 0.5-7.5 m ug/mL for alpha -tocopherol and beta -tocotrienol; 0.5-10 mug/mL for beta - tocopherol; and 0.5-15 mug/mL for alpha -tocotrienol, gamma -tocopherol, ga mma -tocotrienol, and delta -tocopherol. Extensive quality assurance of the proposed method was performed by the sta ndard addition method in both crude and edible oil. For edible oil, the pre cision obtained (n=10) was better than 1.8, 2.0, and 1.4 CV% for alpha, bet a, and gamma -tocopherol, respectively; for crude oil it was better than 1. 9, 2.4, and 2.4% for alpha, beta, and gamma -tocopherol, respectively. Furthermore, for edible oil the mean recovery values were between 96-116%, 58-69%, and 111-115% for alpha, beta, and gamma -tocopherol, respectively; for crude oil recovery values were between 85-95%, 63-66%, and 99-103% for the same tocopherols, respectively. The proposed method appears to be an adequate method for quality control an d helpful for authenticity verification by the official control in oil indu stry.