(7-keto), 6-ketocholesterol (6-keto), 7α-hydroxy-cholesterol
(7α-OH), 7β-hydroxycholesterol (7β-OH),
5,6α-epoxycholesterol (5,6α-EP), 5,6β-epoxycholesterol
(5,6β-EP), 25-hydroxycholesterol (25-OH), 20-hydroxycholesterol (20-OH),
and cholestanetriol (triol)], butylated hydroxytoluene (BHT), pyridine, and
silicic acid (100 mesh) were purchased from Sigma-Aldrich Co., LLC (Korea).
Bis-[trimethylsilyl]-trifluoroacetamide (BSTFA)+1%
trimethylchlorosilane (TMCS) was obtained from Supelco (USA). Hexane, ethyl
acetate, acetone, methanol and chloroform of HPLC grades, celite545, and calcium
phosphate (CaHPO4·2H2O) were purchased from Fisher
Scientific Co. (USA).