Rationale: The hydrogen isotopic composition of lipids (δ 2Hlipid) is widely used in food

science and as a proxy for past hydrological conditions. Determining the δ 2H values of large,

well-preserved triacylglycerides and other uniquely microbial lipids, such as glycerol dialkyl

glycerol tetraether (GDGT) lipids, is thus of widespread interest but has so far not been

possible due to their size which prohibits analysis by traditional gas chromatography

pyrolysis isotope ratio mass spectrometry (GC-P-IRMS).

Methods: We determined the δ 2H values of large, polar molecules and applied high

temperature gas chromatography (GC) methods on a modified GC-P-IRMS system. The

methods were validated using authentic standards of large, functionalised molecules

(triacylglycerides, TAG), purified reference standards of GDGTs, and compared to δ 2H

values determined by elemental analyser pyrolysis isotope ratio mass spectrometry (EA-PIRMS); and subsequently applied to the analysis of GDGTs in a sample from a methane

seep and a Welsh peat.

Results: δ 2H values of TAGs agreed within error between different between GC-P-IRMS and

EA-P-IRMS, with GC-P-IRMS showing 3-5 ‰ precision for 10 ng H injected. Archaeal lipid

GDGTs with up to three cyclisations could be analysed: δ 2H values were not significantly

different between methods with standard deviations of 5 to 6 ‰. When environmental

samples were analysed, δ 38 2H values of isoGDGTs were 50 ‰ more negative than those of

terrestrial brGDGTs.

Conclusions: Our results indicate that the high temperature GC-P-IRMS (HTGC-P-IRMS)

method developed here is appropriate to determine the δ 2H values of TAGs, GDGT lipids

with up to two cyclisations, and potentially other high molecular weight compounds. The

methodology will widen the current analytical window for biomarker and alimentary light

stable isotope analyses. Moreover, our initial measurements suggest that bacterial and

archaeal GDGT δ 2H values can record environmental and ecological conditions

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Determination of the δ 2H Values of High Molecular Weight Lipids by High Temperature GC Coupled to Isotope Ratio Mass Spectrometry

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