The measurement of D/H ratio in alkenones and their isotopic heterogeneity

摘要

Previous paleoenvironmental studies reported the delta D values of a mixture of coeluting alkenones. Here, we present a semi-preparative normal-phase high-performance liquid chromatography-mass spectrometry (NP-HPLC-MS) method for purifying long chain (C-37 and C-38) unsaturated methyl and ethyl ketones (alkenones) on the basis of chain length and degree of unsaturation. The method was applied to purify alkenones in suspended particles and surface sediments from a site in Chesapeake Bay, eastern USA. The hydrogen isotopic composition of di- and triunsaturated C-37 and C-38 alkenones differed significantly oil the basis of chain length and the degree of unsaturation, demonstrating the importance of gas chromatography-isotope ratio-mass spectrometry (GC-irMS) analysis of individual alkenones for accurate paleoenvironmental reconstruction. Constant fractionation factors between alkenones with different chain length but the same degree of unsaturation (alpha(C37:2-C38:2) and alpha(C37:3-C38:3) = 1.01) and those with the same chain length but different degree of unsaturation (alpha(C37:2-C37:3) and alpha(C38:2-C38:3) = 0.97) in all samples suggest that the values may represent hydrogen isotope fractionation associated with elongation and desaturation during alkenone biosynthesis. (C) 2008 Elsevier Ltd. All rights reserved.