EVALUATION OF SOLID-PHASE EXTRACTION AND GAS-CHROMATOGRAPHY FOR DETERMINATION OF CHOLESTEROL OXIDATION-PRODUCTS IN SPRAY-DRIED WHOLE EGG

A method using solid phase extraction (SPE) and capillary gas chromatography (GC) was developed for the rapid quantification of cholesterol oxidation products (COPS) in egg powders. Total lipid extracts were fractionated on disposable silica SPE tubes to isolate COPS from triacylglycerols, phospholipids, and cholesterol. The COPS (alpha- and beta-epoxides, 7 alpha- and 7 beta-hydroxycholesterols, 7-ketocholesterol) were resolved as their trimethylsilyl ether derivatives on a nonpolar capillary column. Combined CC-mass spectrometry was used to confirm the identities of the trimethylsilyl ethers of COPS. Homogeneous and consistently high recoveries of COPS standards as well as 6-ketocholestanol (internal standard), approximately 86%, were achieved with this analytical technique.