Lignan analysis in seed oils from four Sesamum species: Comparison of different chromatographic methods

Different chromatographic methods, thin-layer chromatography (TLC), gas chromatography (GC), gas chromatography/mass spectrometry (GC/MS) and normal- and reversed-phase high-performance liquid chromatography (HPLC), were compared for their ability to separate the different lignans present in four Sesamum species, viz., S. indicum Linn., S. alatum Thonn., S. radiatum Schum & Thonn. and S. angustifolium (Oliv.) Engl. The advantages and limitations of each method are discussed, and a combination of methods is suggested for qualitative analyses. Two-dimensional TLC was found to be a valuable qualitative technique and one-dimensional TLC is useful for preparative purposes. GC is a good supplement for qualitative analysis, but it had many limitations as a quantitative tool-it involves many preparative steps, no suitable internal standard was found to be commercially available and the various lignans had markedly different response factors. GC/MS is a necessary techniqee to confirm the identity of the lignans present. HPLC is a one-step technique suitable for quantitative analyses, and is fast and simple because it involves direct injection of oil solutions. Reversed-phase HPLC was unable to separate sesamolin and sesangolin, but a normal-phase silica column provided satisfactory separation for these two lignans. 2-Episesalation of S. alatum, however, did not elute from the normalphase column. Once lignans are identified, a relevant HPLC method can be used for quantitative analyses. Sesamin was present in large amounts in S. radiatum, in considerable amounts in S. indicum and S. angustifolium, and in small amounts in S. alatum. Sesamolin occurred in considerable amounts in S. indicum and S. angustifolium, but only in small amounts in the other two wild species studied. Sesamum alatum was characterized by high amounts of 2-episesalatin, and S. angustifolium was characterized by high levels of sesangolin.