Gas chromatographic properties of common cholesterol and phytosterol oxidation products

The most common cholesterol and phytosterol oxidation products found in foodstuffs or biological matrices are the 7alpha- and 7beta-hydroxysterol, 7-ketosterol, 5alpha,6alpha- and 5beta,6beta-epoxysterol, and triol derivatives of sterols. This study focused on the preparation and purification of such products derived from campesterol, stigmasterol and beta-sitosterol. The identity of the substances was confirmed by mass spectroscopic analysis. The elution order of a complex mixture composed of the 7alpha- and 7beta-hydroxysterol, 7-ketosterol, 5alpha,6alpha- and 5beta,6beta-epoxysterol, and triol derivatives of cholesterol, campesterol, stigmasterol and beta-sitosterol was recorded on an apolar as well as a medium-polarity capillary column in relation to two commonly used internal standards, i.e. alpha-cholestane and 19-hydroxy cholesterol. Flame-ionization detector as well as mass spectrometry response factors were derived from a gravimetrically prepared mixture of commercially available cholesterol oxide standards. It was proven that the ionization efficiency of cholesterol and phytosterol oxides are very similar and that response factors obtained for cholesterol oxidation products are also valid for quantitative work regarding phytosterol oxidation products.