Capillary gas chromatography/mass spectrometry of cholesteryl esters with negative ammonia chemical ionization

Abstract

Mixtures of both synthetic and naturally occurring (human plasma cholesteryl esters have been examined by capillary gas chromatography/mass spectrometry (GC/MS). A magnetic sector mass spectrometer was used and a variety of ionization modes were assessed with a view to obtaining structural information on intact cholesteryl esters. By employing ammonia as reagent gas, with negative ion scanning, spectra were produced from which the nature of steryl and fatty acyl moieties could be readily deduced. Analyses were performed at an ion source temperature of 300 degrees C in order to maintain the integrity of the gas chromatographic profile. The technique described is of general use for the GC/MS analysis of steryl esters, particularly in conjunction with magnetic sector instruments.

Preliminary Results for the Analysis of Lipids in Ancient Bone

“…The free fatty acids palmitic (C 16:0 ), stearic (C 18:0 ) and oleic (C 18:1 ) acids were evident at shorter retention time than cholesterol, while at longer retention times cholesteryl esters were detectable; their presence being confirmed by GC/MS. Although electron-ionization mass spectrometry was sufficient to confirm the presence of cholesteryl fatty acyl esters through detection of ions arising from the sterol nucleus, determination of the fatty acyl moiety associated with each of the ester peaks will require the use of chemical ionisation mass spectrometry (Evershed & Goad, 1987;Evershed, 1992). Further investigation of the cholesteryl fatty acyl ester fraction in this manner is currently in progress.…”

Analysis of cholesteryl esters and diacylglycerols using lithiated adducts and electrospray ionization-tandem mass spectrometry

“…However, GC/MS analysis of CEs and DAGs requires a derivatization step (e.g., silyl reagents for electron impact ionization (EI) [22–24], and pentafluorobenzoyl reagents for negative ion chemical ionization (NICI) [22, 25, 26]) to impart the necessary volatility and detection enhancement required for sensitive GC/MS analysis. Thus, attention has focused on the utility of softer ionization techniques for CE and DAG analyses, specifically the use of matrix-assisted laser desorption/ionization (MALDI) [27] and electrospray ionization (ESI) [28–30].…”

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

“…1. A Pye Unicam 204 gas chromatograph linked to a VG 7070H double-focusing magnetic sector mass spectrometer (VG Analytical Ltd., Manchester, UK) via an interface oven that had been modified for high-temperature operation (300-350 0c) [20]. The analytical column was a Quadrex aluminum clad 25-m x 0.25-mm-i.d.…”

“…An alternative approach that has been developed for the HT-GC/MS analysis of intact acyl lipids [20][21][22][23][24][25][26], which include triacylglycerols [19], involves the use of NICI. Ammonia NICI is especially compatible with HT-GC/MS because useful spectra are produced from a wide range of acyl lipids at an ion source block temperature of -300°C.…”

“…Ammonia NICI is especially compatible with HT-GC/MS because useful spectra are produced from a wide range of acyl lipids at an ion source block temperature of -300°C. In the case of triacylgylcerols, very simple spectra are produced that are dominated by [ arise via a nucleophilic gas-phase ammonolysis reaction by analogy with the behavior of the steryl fatty acyl esters under analogous source conditions [20,25].…”