Pressurized liquid extraction prior to liquid chromatography with electrochemical detection for the analysis of vitamin E isomers in seeds and nuts

Pressurized liquid extraction (PLE) was used to isolate tocopherols from seeds and nuts. Very clean extracts were obtained, which were injected directly into the chromatographic system. This enables rapid and simple control in food analysis. The PLE extraction temperature was set at 50 °C, with two cycles of extraction, a static time of 5 min, and acetonitrile as the extraction solvent. LC separation was accomplished on a Synergi Hydro-RP column with methanol–water (99.9:0.1, v/v) containing 2.5 mM acetic acid/sodium acetate buffer, as eluent. Coulometric detection, with a porous graphite electrode at +700 mV, was used. The method was successfully applied to the determination of α-, (β + γ)- and δ-tocopherols in almonds, sunflower seeds, hazelnuts and walnuts. The recoveries were in the 82–110% range. The results were validated with those obtained using sample treatment including alkaline hydrolysis.