Elution behavior of unsaponifiable lipids with various capillary electrochromatographic stationary phases

Capillary electrochromatographic (CEC) separations of unsaponifiable lipids, tocopherols (T), tocotrienols (T3), and plant sterols were studied under various conditions. Investigated stationary phases include pentafluorophenylsilica (PFPS), triacontylsilica (TCS), and octadecylsilica (ODS) phases. A baseline separation of four sterols (ergosterol, lanosterol, sitosterol and stigmasterol) on ODS was achieved and their elution order was found to be dictated by side-chain structures. CEC of the tocol-derived compounds on PFPS in aqueous methanol yielded the most satisfactory results with complete resolution of all components eluting in the order δT3>βT3>γT3>ϵP>αT3>δT>ζ2T>βT>γT>αT, while a reversal in elution of the ϵT–αT3 pair was observed in aqueous acetonitrile. CEC with a TCS phase in non-aqueous methanol led to a different elution pattern δT3>γT3>βT3>αT3ϵT>δT>(ζ2+γ)T>βT>αT, despite favorable resolution of the (γ–ζ2)T pair along with the observation of inseparable(β–γ)T and (β–γ)T3 pairs in non-aqueous dimethylformamide. Non-aqueous acetonitrile mobile phases provided unique selectivity for the (γ–ζ2)T pair and isomer separations on TCS. Variations in separation and retention factors of relevant antioxidant species with CEC variables were evaluated. Examples of CEC quantification of unsaponifiable fractions of rice bran oils and soybean oils are presented.