Evaluating the Isolation and Quantification of Sterols in Seed Oils by Solid-Phase Extraction and Capillary Gas–Liquid Chromatography

A faster and more efficient way of isolating and subsequently cleaning up the sterol fraction obtained from seed oils was developed based on an existing established method that used thin-layer chromatography (TLC) to isolate the sterol fraction (3). The newly developed method used solidphase extraction (SPE) to separate the sterol fraction from other compounds found in the unsaponifiable portion of the seed oils. Toivo and co-workers (4) developed a slightly different method that incorporated the same approach, used SPE rather than TLC, and resulted in excellent recovery results. However, their work investigated only two types of oils and provided no comparative data to existing, established methods. In our study, we performed two tests using the SPE approach for sample isolation and cleanup. The first test compared sterol results obtained through SPE with those of Traditional methods of sterol fraction analysis involve saponification of the seed oil, solvent extraction of the unsaponifiable compounds, and a second isolation of the sterols by thin-layer chromatography (TLC). Solvent extraction of the sterols from the TLC medium is followed by a derivatization step to reduce peak tailing caused by some gas–liquid chromatography column stationary phases. If a capillary column is used, as was the case in this study, the free sterols can be analyzed directly without derivatization. The method reported in this article circumvents TLC, along with its time-consuming multiple steps, and incorporates solid-phase extraction (SPE) columns, which enable quicker and easier sterol isolation and cleanup, thus greatly reducing the number of steps and sample preparation time. The authors describe two tests performed using SPE. The first test involved comparing the SPE method for sterol isolation and cleanup of four refined seed oils with the established TLC method according to American Oil Chemists Society official method Ch 6-91. The second test analyzed six crude seed oils using the SPE approach and compared the results with literature values. Evaluating the Isolation and Quantification of Sterols in Seed Oils by Solid-Phase Extraction and Capillary Gas–Liquid Chromatography