Comparison of Solid-Phase Extraction Methods for the Cleanup of Cholesterol Oxidation Products

Cholesterol oxidation products (COPs) may accumulate in foods of animal origin during processing or storage. As they represent a potential health risk, a need exists for rapid and efficient methods to monitor the occurrence of COPs in the human diet. Methods involving saponification to remove triacylglycerols suffer from artifact formation; therefore, alternatives involving solid-phase extraction (SPE) cartridges have been proposed. The efficiencies of several SPE methods for the cleanup of COPs were compared, and a combination of a silica cartridge followed by an NH2 cartridge was found to be optimal for the removal of matrix components. COPs added at the 150 ppb level to milk fat were recovered by the method proposed ≥90% except cholestanetriol, for which the recovery rate was only 52%. Separation and quantification of COPs were done by GC/MS in full-scan mode. Splitless injection of COPs at a concentration of 0.3 ng/μL produced signal-to-noise ratios between 1:10 and 1:200 for epoxycholesterol and 7β-hydroxycholesterol, respectively. Keywords: Cholesterol oxidation products; oxysterols; solid-phase extraction; milk fat; GC/MS