Beatriz P. P. Oliveira

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.

Development and Evaluation of a Normal Phase Liquid Chromatographic Method for the Determination of Tocopherols and Tocotrienols in Walnuts

Abstract A high performance liquid chromatographic (HPLC) method for the determination of tocopherols and tocotrienols in walnut samples is described. The compounds were extracted with n‐hexane, using a simple solid‐liquid extraction procedure. Tocol was used as internal standard and BHT as anti‐oxidant. The chromatographic separation was achieved using an Inertsil 5 SI normal phase column operating with isocratic elution of n‐hexane/1,4‐dioxane (96.5∶3.5, v/v), at a flow rate of 0.7 mL/min. The effluent was monitored by a series arrangement of a diode‐array detector followed by a fluorescence detector. The detection limits were low, between 0.037 and 0.266 µg/mL. The method was precise (% CV less than 2.8%), accurate (% CV less than 5.6%), and, as a general rule, the recovery values were high (mean values ranging from 93.4% to 104.0%).