RATIONALE: Compound-specific stable hydrogen isotope analysis of fatty acids is being used increasingly as a means of deriving information froma diverse range of materials of archaeological, geological and environmental interest. Preparative steps required prior to isotope ratio mass spectrometry (IRMS) analysis have the potential to alter determined dDvalues and hence must be accounted for if accurate dD values for target compounds are to be obtained.
METHODS: Myristic, palmitic, stearic, arachidic and behenic saturated fatty acids were derivatised to their respective fatty acid methyl esters (FAMEs), using 14% (w/v) boron trifluoride in methanol then analysed by gas chromatography/thermal conversion/IRMS (GC/TC/IRMS). FAMEs generated from fatty acid sodiumsalts of unknown dD valueswere then used to test a correction factor determined for this method of derivatisation.
RESULTS: Derivatisation was found to alter the hydrogen isotopic composition of FAMEs although this effect was reproducible and can be accounted for. The difference between the mean corrected and mean bulk dD values was always less than 6.7 %. Extraction of saturated fatty acids and acyl lipids from samples, subsequent hydrolysis, then separation on a solid-phase extraction cartridge, was found to alter the determined dD values by less than one standard deviation.
CONCLUSIONS: Overall, it has been shown that for natural abundance hydrogen isotope determinations, the isolation and derivatisation of extracted fatty acids alters the determined dD values only by a numerical increment comparable with the experimental error. This supports the use of the described analytical protocol as an effectivemeans of determining fatty acid dD values by GC/TC/IRMS. Copyright (C) 2012 John Wiley & Sons, Ltd.