Determination of campesterol, stigmasterol, and beta-sitosterol in saw palmetto raw materials and dietary supplements by gas chromatography: single-laboratory validation

In conjunction with an AOAC Presidential Task Force on Dietary Supplements, a method was validated for measurement of 3 plant sterols (phytosterols) in saw palmetto raw materials, extracts, and dietary supplements. AOAC Official Method 994.10, "Cholesterol in Foods," was modified for purposes of this validation. Test samples were saponified at high temperature with ethanolic potassium hydroxide solution. The unsaponifiable fraction containing phytosterols (campesterol, stigmasterol, and beta-sitosterol) was extracted with toluene. Phytosterols were derivatized to trimethylsilyl ethers and then quantified by gas chromatography with a hydrogen flame ionization detector. The presence of the phytosterols was detected at concentrations greater than or equal to 1.00 mg/100 g based on 2-3 g of sample. The standard curve range for this assay was 0.00250 to 0.200 mg/mL. The calibration curves for all phytosterols had correlation coefficients greater than or equal to 0.995. Precision studies produced relative standard deviation values of 1.52 to 7.27% for campesterol, 1.62 to 6.48% for stigmasterol, and 1.39 to 10.5% for beta-sitosterol. Recoveries for samples fortified at 100% of the inherent values averaged 98.5 to 105% for campesterol, 95.0 to 108% for stigmasterol, and 85.0 to 103% for beta-sitosterol.