Determination of the ? ² H values of high molecular weight lipids by high?temperature gas chromatography coupled to isotope ratio mass spectrometry

Rationale The hydrogen isotopic composition of lipids (?2Hlipid) is widely used in food science and as a proxy for past hydrological conditions. Determining the ?2H values large, well-preserved triacylglycerides other microbial lipids, such glycerol dialkyl tetraether (GDGT) thus widespread interest but has so far not been possible due to their low volatility which prohibits analysis by traditional gas chromatography/pyrolysis/isotope ratio mass spectrometry (GC/P/IRMS). Methods We determined polar molecules applied high-temperature chromatography (HTGC) methods on modified GC/P/IRMS system. system 7-m GC column, glass Y-splitter thermal mass. were validated using authentic standards functionalised (triacylglycerides, TGs), purified GDGTs. results compared with elemental analyser/pyrolysis/isotope (HTEA/P/IRMS), subsequently GDGTs sample from methane seep Welsh peat. Results TGs agreed within error between HTGC/P/IRMS HTEA/IRMS, showing larger errors. Archaeal lipid up three cyclisations could be analysed: significantly different standard deviations 5 6 ‰. When environmental samples analysed, isoGDGTs 50 ‰ more negative than those terrestrial brGDGTs. Conclusions Our indicate that method developed here appropriate determine TGs, two cyclisations, potentially high molecular weight compounds. methodology will widen current analytical window biomarker light stable isotope analyses. Moreover, our initial measurements suggest bacterial archaeal GDGT can record ecological