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Routine gas chromatographic/mass spectrometric analysis of fatty acid methyl esters using the ion trap detector.

About 60 long-chain fatty acids occur naturally in lipids of biological tissues and fluids, oils, fats and waxes. The ion trap detector (ITD) offers a convenient but powerful means for the routine analysis by gas chromatography/mass spectrometry of such fatty acids as their methyl esters (FAMES). Enhanced [M + 1]+ ions may be formed at higher sample levels of 50 ng or more. However, spectra still retain a predominantly electron impact (EI) character. Using the classical mass spectral performance test compound methyl stearate as an example, good library comparisons were obtained for spectra run over a dynamic range of 2 pg to 225 ng, when a mid-range ITD spectrum run on 7.5 ng was used as a reference. Almost equally good spectral comparisons were found with literature reference spectra run on both quadrupole and sector conventional mass spectrometers. Using human plasma phospholipid FAMES as an example, along with an ITD-generated EI spectral library of FAMES standards, it was seen that for most of the components present the mass spectral library comparison was good enough to permit identification based on mass spectrometry alone. For all components, a combination of gas chromatographic retention index and mass spectral information permitted an unequivocal identification.