Tocopherol analysis
Tocopherols in oil was determined with an HPLC (Shimadzu Prominence iSeries, Kyoto, Japan) equipped photodiode array (PDA) and a fluorescence detector in series (Hwang et al., 2017). Oil sample (about 10 mg) dissolved in hexane:THF (97:3 v/v, 1 ml) was injected to onto a YMC-Pack Diol 120 NP column (150 x 3.0 mm, 5 µm, YMC America, Allentown, PA, USA) and eluted with hexane/THF (97:3 v/v) at a flow rate of 1.0 ml/min. The PDA was set to scan from 200-500 nm and collect data at 295 nm for tocopherol verification. Quantitation was performed with the fluorescence detector set at 344 nm (emission) after excitation at 292 nm. Each tocopherol was identified using commercial standards. External standard curves per tocopherol were used for quantitative analysis.