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 preparation only involves a dissolution of the oil in n-hexane and filtration. The chromatographic separation was achieved using a normal phase column LiChrosorb SI 60 (5 μm; 25.0 × 0.4 cm). Isocratic elution was carried out using n-hexane : 2-propanol (99.7:0.3). The effluent was monitored by using diode-array and fluorimetric detectors. The determinations were performed in the following linear ranges: 0.5-7.5 μg/mL for α-tocopherol and β-tocotrienol; 0.5-10 μg/mL for β-tocopherol; and 0.5-15 μg/mL for α-tocotrienol, γ-tocopherol, γ-tocotrienol, and δ-tocopherol. Extensive quality assurance of the proposed method was performed by the standard addition method in both crude and edible oil. For edible oil, the precision obtained (n=10) was better than 1.8, 2.0, and 1.4 CV% for α, β, and γ-tocopherol, respectively; for crude oil it was better than 1.9, 2.4, and 2.4% for α, β, and γ-tocopherol, respectively. Furthermore, for edible oil the mean recovery values were between 96-116%, 58-69%, and 111-115% for α, β, and γ-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 and helpful for authenticity verification by the official control in oil industry.