Biomarker carbon isotope analyses

Biomarker Carbon-Isotope Analyses. While a forest/non-forest carbon-isotope signature is readily identifiable in terrestrial environments, it is very difiScult to obtain complete, well dated fluvial sequences. Complete sedimentary sequences are readily available fi-om the submarine fan deposits which lie off the mouth of the Amazon River 82 but the analysis of bulk sediments fi om the marine environment is not appropriate because terrestrially-derived riverbome carbon in the sample rapidly becomes mbced with marine-derived carbon offshore fi om the river mouth. 

Boschker, H.T.S., de Brower, I.F.C., and Cappenberg, T.E. (1999) The contribution of macrophyte-derived organic matter to microbial biomass in salt-marsh sediments Stable carbon isotope analysis of microbial biomarkers. Limnol. Oceanogr. 44, 309-319. 

Newer instrumental methods of potential utility in organic analysis of environmental and geological biomarkers are compound specific isotope analysis (CSIA) and carbon-14 dating with accelerator mass spectrometry (AMS). CSIA provides the carbon isotope composition of individual... 

Carbon isotopic composition of individual biomarkers in gilsonites (Utah). In Compound-specific Analysis in Biogeochemistry and Petroleum Research (eds. M.Schoell and J. M. Hayes). Org. Geochem. 21, 673-683. 

The molecular distribution and compound-specific carbon-isotopic composition of hydrocarbons can be used to qualify and quantify their sources and pathways in the environment. Molecular source apportionment borrows from molecular methods that were developed and applied extensively for fundamental oil biomarker studies, oil-oil and oil source rock correlation analysis. Additionally, petroleum refinement produces well-defined mass and volatility ranges that are used as indicators of specific petroleum product sources in the environment. Compound-specific carbon-isotopic measurement is a more recent addition to the arsenal of methods for hydrocarbon source apportionment. Carbon isotopic discrimination of i-alkanes, biomarkers, and PAHs has shown that the technique is highly complementary to molecular apportionment methods. 

Recent advances in isotope analysis include the ability to analyse isotopically smaller proportions of individual compounds by the use of more sensitive online isotope ratio mass spectrometers (cf. Merritt Hayes 1994 Merritt et al. 1994) and stable carbon isotope determination of individual n-alkanes, isoprenoids and biomarkers in petroleums is now a standard tool. Despite early work on collection of chromato-graphically separated individual n-alkanes followed by combustion and isotope determination (Welte 1969) it was for a number of years impossible to analyse isotopically long chained alkanes with the same comfort and ease as the... 

Pathways of carbon flow in natural environments have also been reconstracted using bulk stable carbon and nitrogen isotopes as well as compound-specific isotopic analysis of individual biomarker lipid component (Hayes et al, 1990) based on the fractionations involved during primary (photosynthetic) and secondary (heterotrophic) processes. Recently, compound-specific radiocarbon analysis of individual biomarker hpid has been shown to be a valuable technique to determine the source of marine organic matter (Eglinton et al., 1997). 

From metabolic studies, an isotopic caffeine breath test has been developed that detects impaired liver function using the quantitative formation of labeled carbon dioxide as an index. From the urinary excretion of an acetylated uracil metabolite, human acet-ylator phenotype can be easily identified and the analysis of the ratio of the urinary concentrations of other metabolites represents a sensitive test to determine the hepatic enzymatic activities of xanthine oxidase and microsomal 3-methyl demethylation, 7-methyl demethylation, and 8-hydroxylation. Quantitative analyses of paraxanthine urinary metabolites may be used as a biomarker of caffeine intake. Fecal excretion is a minor elimination route, with recovery of only 2-5% of the ingested dose. 

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