Measurement of deuterium incorporation into fatty acids by gas chromatography isotope ratio mass spectrometry

A continuous-flow pyrolysis interface for gas chromatography/isotope ratio mass spectrometry (GC/IRMS) has been developed for delta(2)H analysis of in dividual organic compounds. Pyrolysis of gas chromatographically separated fatty acid methyl esters is performed at 1200 degrees C in an unpacked alum ina tube to convert nanomole quantities of individual compounds to H-2. Hyd rogen is separated from other gaseous pyrolysis products on a solid-phase c apillary column prior to its entering the mass spectrometer. Use of an isot ope ratio mass spectrometer with high mass dispersion ensures (HH)-H-2-H-1: (HH)-H-1-H-1 ratio measurement is accurately made in the presence of a larg e excess of helium carrier gas. The technique has been applied to the measurement of lipid synthesis in hum ans, using deuterium oxide (D2O) incorporation into fatty acids, Using safe body water deuterium enrichments (<0.5%) the labelled fatty acids are unli kely to contain more than one deuterium per molecule, and show similar chro matographic behaviour to natural abundance samples, Following overnight inc orporation of D2O, plateau palmitate enrichments were measured by GC/IRMS w ith a relative standard deviation (RSD) of similar to 0.5%, This compares f avourably with GC/MS measurements for which an RSD of 5 to 10% would be exp ected for similar samples. Compared to off-line sample conversion and IRMS, the current approach is much less laborious and gives information on indiv idual fatty acids rather than the mixed triacylglycerols, Copyright (C) 199 9 John Wiley & Sons, Ltd.