Gas chromatography with mass spectrometry analysis of 4,4-dimethylsterols and 4-methylsterols in edible oils after their enrichment by means of solid phase extraction

4-Methylsterols (4-M-sterols) and 4,4-dimethylsterols (4,4-D-sterols) are a group of underexplored minor sterols that occur in almost all living organisms. Here, we developed a strategy for the determination of the biochemical precursors of the predominant 4-desmethylsterols in edible oils. Due to their low contribution to the sterol content in the samples, a solid phase extraction (SPE) method was developed for the enrichment of 4-M- and 4,4-D-sterols in the hexane extracts of saponified oils. In a two-fold SPE procedure, the bulk of 4,4-D-sterols was collected in one fraction. The residual sample was subjected to a second SPE step which targeted all 4-M-sterols and low shares of 4,4-D-sterols in one fraction and the predominant 4-desmethylsterols in another one. After silylation of the SPE fractions, gas chromatography with mass spectrometry (GC/MS) was used to analyze 4,4-D- and 4-M-sterols. The results were used to define eight subgroups whose characteristic structural features could be linked with the presence of specific m/z values. These m/z values were measured sensitively by GC/MS operated in selected ion monitoring (SIM) mode. Application of the GC/MS method to eighteen edible oils enabled the detection of 55 mostly very low abundant 4-M- and 4,4-D-sterols. Twenty-four of the 4-M- and 4,4-D-sterols could be assigned and the remaining 31 unknown sterols could be traced back to their basic structures.