A Rapid Method for the Simultaneous Analysis of Tocopherols and Tocopherol Quinones in Edible Oils Using Normal-Phase High-Performance Liquid Chromatography

A normal-phase high-performance liquid chromatography (HPLC) method with UV spectrophotometric detector (SPD) detection was established for the simultaneous analysis of four tocopherol (TP) homologues and their corresponding tocopherol quinones (TQs). Separation was performed on a Sepax Technologies silica column (4.6 mm × 250 mm, 5 μm) using a mobile phase consisting of n-hexane, isopropanol, and tetrahydrofuran, allowing the eight target compounds to be effectively separated within 15 min. Method validation was conducted using standard solutions prepared in n-hexane, providing a direct evaluation of the chromatographic performance under a relatively clean solvent system. The method showed satisfactory linearity, with R2 values of 0.9850–0.9996. The limit of detection (LOD) and limit of quantification (LOQ) ranges were 0.140–0.371 and 0.467–1.235 μg/mL for TP homologues and 0.0564–0.0856 and 0.1708–0.2595 μg/mL for TQ homologues, respectively. Precision was acceptable, with intra-day and inter-day relative standard deviations (RSD) below 2.69% and 3.78%, respectively. To further evaluate its applicability in oil matrices, recovery experiments were performed in peanut oil and camellia oil, yielding recoveries of 91.7–105.8% and 90.9–97.7% for TP homologues and 82.8–98.7% and 79.5–101.8% for TQ homologues, respectively. The method was further applied to edible oil samples. The results showed that the major TP homologues and detectable TQ homologues were determined, while some homologues were below the detection limits. Overall, the proposed method offers a simple and practical approach for the simultaneous analysis of TP and TQ homologues, thereby supporting further investigation of tocopherol oxidation in edible oils.