Simultaneous determination of plasmatic phytosterols and cholesterol precursors using gas chromatography-mass spectrometry (GC-MS) with selective ion monitoring (SIM).

Phytosterols (beta-sitosterol, cholestanol and campesterol) and cholesterol precursors (desmosterol and lathosterol), have been suggested as important biochemical markers of intestinal cholesterol absorption and liver biosynthesis, respectively, and as useful clinical parameters in the study of hypercholesterolemia, beta-sitosterolemia, atherosclerosis and cardiovascular disease, including pharmacological response to hypolipidemic agents. We developed an optimised analytical method for the simultaneous analysis of cholestanol, desmosterol, lathosterol, campesterol and beta-sitosterol in plasma using capillary gas chromatography coupled to mass spectrometry (GC-MS) with multiple selected ion monitoring (SIM). This method is based on the alkaline hydrolysis of sterol esters, extraction of free sterols and derivatization. The recovery of all sterols was in the range 76-101%. Within-day relative standard deviations (R.S.Ds.) and the between-day R.S.Ds. of cholestanol, desmosterol, lathosterol, campesterol and beta-sitosterol were less than 8%, and their plasma levels in 161 normal subjects were (mean+/-S.D.) 4.73+/-2.57, 2.37+/-1.04, 6.23+/-3.14, 3.67+/-1.95 and 5.92+/-3.62 micromol/l, respectively.