Abstract
A continuous-flow pyrolysis interface for gas chromatography/isotope ratio mass spectrometry (GC/IRMS) has been developed for δ2H analysis of individual organic compounds. Pyrolysis of gas chromatographically separated fatty acid methyl esters is performed at 1200 °C in an unpacked alumina tube to convert nanomole quantities of individual compounds to H2. Hydrogen is separated from other gaseous pyrolysis products on a solid-phase capillary column prior to its entering the mass spectrometer. Use of an isotope ratio mass spectrometer with high mass dispersion ensures 2H1H:1H1H ratio measurement is accurately made in the presence of a large excess of helium carrier gas. The technique has been applied to the measurement of lipid synthesis in humans, using deuterium oxide (D2O) incorporation into fatty acids. Using safe body water deuterium enrichments (<0.5%) the labelled fatty acids are unlikely to contain more than one deuterium per molecule, and show similar chromatographic behaviour to natural abundance samples. Following overnight incorporation of D2O, plateau palmitate enrichments were measured by GC/IRMS with a relative standard deviation (RSD) of ∼0.5%. This compares favourably with GC/MS measurements for which an RSD of 5 to 10% would be expected for similar samples. Compared to off-line sample conversion and IRMS, the current approach is much less laborious and gives information on individual fatty acids rather than the mixed triacylglycerols. Copyright © 1999 John Wiley & Sons, Ltd.
Published Version
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