LIGNAN ANALYSIS IN SEED OILS FROM 4 SESAMUM SPECIES - COMPARISON OF DIFFERENT CHROMATOGRAPHIC METHODS

Different chromatographic methods, thin layer chromatography (TLC), ga s chromatography (GC), gas chromatography/mass spectrometry (GC/MS) an d normal- and reversed-phase high-performance liquid chromatography (H PLC), were compared for their ability to separate the different Lignan s present in four Sesamum species, viz., S. indicum Linn., S. alatum T honn, S. radiatum Schum and Thonn. and S. angustifolium (Oliv.) Engl. The advantages and limitations of each method are discussed, and a com bination of methods is suggested for qualitative analyses. Two-dimensi onal TLC was found to be a valuable qualitative technique and one dime nsional TLC is useful for preparative purposes. GC is a good supplemen t for qualitative analysis, but it had many limitations as a quantitat ive tool-it involves many preparative steps, no suitable internal stan dard was found to be commercially available and the various lignans ha d markedly different response factors. GC/MS is a necessary technique to confirm the identity of the lignans present. HPLC is a one-step tec hnique suitable for quantitative analyses, and is fast and simple beca use it involves direct injection of oil solutions. Reversed-phase HPLC was unable to separate sesamolin and sesangolin, but a normal phase s ilica column provided satisfactory separation for these two lignans. 2 -Episesalatin of S. alatum, however, did not elute from the normal-pha se column, Once lignans are identified, a relevant HPLC method can be used for quantitative analyses. Sesamin was present in large amounts i n S. radiatum, in considerable amounts in S. indicum and S angustifoli um, and in small amounts in S. alatum. Sesamolin occurred in considera ble amounts in S. indicum and S. angustifolium, but only in small amou nts in the other two wild species studied. Sesamum alatum was characte rized by high amounts of 2-episesalatin, and S. angustifolium was char acterized by high levels of sesangolin.