Characterization of tetramethylammonium hydroxide thermochemolysis products of near-shore marine sediments using gas chromatography/mass spectrometry and gas chromatography/combustion/isotope ratio mass spectrometry

Abstract

The study describes the application of gas chromatography/mass spectrometry (GC/MS) and gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) to characterize the molecular and compound-specific stable carbon isotope composition, respectively, of tetramethylammonium hydroxide (TMAH) thermochemolysis products of organic matter present in marine sediments. The objective of the study was to examine the usefulness of TMAH thermochemolysis products in identifying organic markers of terrestrial-derived sources in marine sediments. ‘Batch-wise’ thermochemolysis conditions (excess TMAH. 250 °C, sealed glass tube, 30 min) were used on sediments and standards. Compound-specific isotope analysis (CSIA) of standards showed no evidence of isotopic fractionation at methyl carbon during methylation of a number of phenolic acid and fatty acid compounds. It was also shown that no appreciable isotopic affect occurs during bond cleavage and methylation of fatty acid groups of the standard triglyceride, tricaprin. These preliminary tests indicate that the initial δ 13C composition of chemical markers containing acidic functional groups can be obtained by measuring the δ 13C of the corresponding methyl esters and/or ethers after TMAH methylation. In order to confirm the number of methoxy groups in lignin-derived markers, tetraethylammonium hydroxide was employed. Useful chemical markers found in near-shore sediments in reasonable abundance were a range of fatty acids, vanillin, vanillic acid and P-coumaric acid. Preliminary results of CSIA of these phenolic markers and selected saturated fatty acids in three different marine sediment cores are reported.