Determination of RS,E/Z-tocotrienols by HPLC

Synthetic α-tocotrienol was separated into four geometrical E/Z side chain isomers by preparative HPLC (permethylated β-cyclodextrin phase). The isolated isomers were resolved in ethylene glycol dimethyl ether, converted into the corresponding methyl ether using dimethyl sulfate, and the tocotrienol methyl ethers were extracted with n-hexane. A subsequent HPLC separation on a chiral phase (adsorbent cellulose derivated with 3,5-dimethyl phenyl carbamate) discriminates between the enantiomers of each E/Z side chain isomer, achieving the complete resolution of the eight occurring synthetic RS,E/Z-α-tocotrienols. The method can be shortened by omitting the preparative separation of the E/Z tocotrienol isomers prior to the chromatography on the chiral dimethyl phenyl carbamate phase. The simplified method achieved the following separation: RS,E/Z-α-tocotrienol separated into five peaks, RS,E/Z-β-tocotrienol into eight, RS,E/Z-γ-tocotrienol into six and RS,E/Z-δ-tocotrienol into eight peaks. The naturally occurring R,E-E-tocotrienol isomer could be identified within the synthetic RS,E/Z-isomers by co-chromatography with tocotrienol methyl ethers derived from natural sources, respectively.