Gas chromatographic–mass spectrometric determination of plasma saturated fatty acids using pentafluorophenyldimethylsilyl derivatization

An improved method for the detection of 11 saturated fatty acids (SFAs) including C12:0–C26:0 (even numbers only), C17:0, C19:0 and C23:0 in human plasma by gas chromatography–mass spectrometry (GC–MS) with a stable isotope internal standard as d3-stearic acid is described. This procedure was based on acidic treatment, liquid–liquid extraction, and chemical derivatization prior to instrumental analysis. Eleven pentafluorophenyldimethylsilyl-SFA derivatives were well separated without any interfering peaks in plasma samples. The characteristic ions at M−15, constituting the base peaks in the electron impact mass spectra for 11 SFAs, permitted their sensitive detection by GC–MS in the selected ion monitoring (SIM) mode. The SIM responses were linear with correlation coefficients varying from 0.993 to 0.999 in the concentration range of 0.05∼50 μg/ml for the 11 SFAs. The detection limits for SIM of the SFAs varied in the range of 0.05∼10.0 pg. When applied to the plasma samples of normal subjects and patients with X-linked adenoleukodystrophy, which is one of the hereditary peroxisomal disorders, the present method enabled us to determine the SFAs with good sensitivity and good overall precision and accuracy within the concentration ranges of 0.14∼82.35 μmol/l.