Capillary gas chromatography/mass spectrometry of intact fatty acyl esters of pregnane steroids

Mass spectrometric profiling of saturated fatty acid esters of steroids separated by high-temperature gas chromatography

An efficient analytical method for simultaneous determination of 12 SFEs in serum is described. The method involves solid-phase extraction to isolate of SFEs from interfering species, especially cholesteryl esters, conversion to trimethylsilyl (TMS) ether derivatives for the direct analysis by gas chromatography-mass spectrometry (GC-MS) using a high temperature MXT-1 (Silcosteel-treated stainless steel) capillary column. All SFEs as their TMS derivatives were well separated with excellent peak shapes within 12 min. Overall recoveries ranged from 88% to 119%, with a detection limits for SFEs ranged from 2 to 30 microg L(-1). The linearity as correlation coefficient was higher than 0.99 except for pregnenolone-3-arachidate (r(2)=0.98) in the concentration range of 5-3000 microg L(-1). Ten serum samples obtained from volunteers were also analyzed and quantitatively determined of DHEA-3-palmitate and pregnenolone-3-stearate in 1.8-1195.8 microg L(-1) concentration. The devised high temperature GC-MS method could be useful for identification of SFEs in biological specimens including serum.

High-resolution triacylglycerol mixture analysis using high-temperature gas chromatography / mass spectrometry with a polarizable stationary phase, negative ion chemical ionization, and mass-resolved chromatography

High-temperature gas chromatography/mass spectrometry (HT-GC/MS) has been employed to study the behavior of mixtures of triacylglycerol molecular species on a polarizable stationary phase (immobilized 65% phenyl methyl silicone). The use of negative ion chemical ionization (NICI) at an ion source block temperature of 300 °C overcomes problems with interpretation of electron ionization (EI) mass spectra produced during the HT-GC/MS. The NICI spectra of triacylglycerols produced under these conditions contain abundant [RCO2](-), [RCO2 - 18](-), and [RCO2 - 19](-) ions, believed to be produced by nucleophilic gas-phase ammonolysis, that are used to identify the individual fatty acid moieties associated with peaks in triacylglycerol total ion chromatograms. The polarizable stationary phase produces significantly enhanced resolution of triacylglycerol molecular species compared to hightemperature stable apolar stationary phases, such as immobilized dimethyl polysiloxanes. The resolution of complex natural mixtures of triacylglycerols can be further improved by use of the Biller-Biemann enhancement technique to produce mass-resolved chromatograms. Investigation of the mass-resolved chromatograms provides important information with regard to the factors that affect elution orders of individual triacylglycerol molecular species. The analysis of mixtures of authentic triacylglycerols by HT-GC/MS via NICI provides data that relate to the analytical limits of the technique for the analysis of triacylglycerols that bear both saturated and polyunsaturated fatty acyl moieties.