A GC/MS based method for the thorough analysis of sterols in food

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Sterols are bioactive lipid compounds virtually found in all food samples at concentrations of ~1% of the total lipids. This substance class exists in a variety of over 250 individual compounds. However, very few are available as reference standards, and less than 20 can be measured in routine analysis by existing routine methods. During the analysis of samples, many of the sterols are overlooked, and labelled unknown or wrongly. In addition, determination of minor sterols was reported to be prone to errors. The goal of this project is the development of a sensitive GC/MS method that allows the thorough analysis of all sterols in and from food samples. For this purpose, a new concept based on Kováts indices was developed using self-synthesized fatty acid pyrrolidine esters (pyrrolidides) as reference compounds in combination with a highly sensitive GC/MS selected ion monitoring (SIM) screening method that allows to assign structures to trace sterols (contribution <0.01% to the lipids). Tentatively identified sterols will be enriched/isolated by means of countercurrent chromatography (CCC) and other methods (hydrogenation, solid phase extraction) followed by structure investigation by GC/MS and NMR. Several deuterium labelled compounds will be synthesized for use as internal standards for quantification. All data will be merged in a comprehensive data base that will allow users to determine sterols reliably for different purposes.