Hiroshi Naraoka

PAHsに関する最新の研究の提言として、炭素・水素安定同位体比を用いた研究の可能性について論述している。

We established a separation procedure of sedimentary straight-chain and cyclic fatty acids by urea adduction to facilitate GC/C/IRMS analysis. The procedure involves a mixing of the monocarboxylic methyl ester fraction with 15% (w/v) urea in MeOH (200μl), ethyl acetate (300μl) and n-pentane (500μl) at room temperature. After drying the solvents under N₂ flow, the non-adduct fraction (cyclic compounds) is washed with n-hexane (3×1.5ml) (mean recovery: 91%). The residue is dissolved in water (4ml) and the adduct fraction (straight-chain compounds) is subsequently extracted with n-hexane/ether (9:1v/v; 3×1.5ml) (mean recovery: 87%). The separation we apply here was confirmed not to affect the isotopic composition of the straight-chain and the cyclic fatty acids.

Compound-specific isotope analysis has been developed recently using gas chromatography/combustion/mass spectrometry (GC/C/IRMS). This paper summarizes principles and progress of GC/C/IRMS, and reviews recent some important works using this new method. GC/C/IRMS is a novel tool for (i) biomarker analysis in sediments and living matter, (ii) paleoenvironment analysis including reconstruction of ancient biogeochemical processes, (iii) geochemical cycle study of organic compounds in a terrestrial-marine system, (iv) evaluation of maturity and diagenesis of organic matter including petroleum formation, (v) ecological analysis, (vi) evaluation of anthropologenic pollution in environment, (vii) detection of extraterrestrial organic compounds and the formation mechanism study, (viii) tracer studies in environment.

An isolation procedure of microgram amounts of long-chain n-alkanes from crude oil using molecular sieve was examined for its applicability to stable carbon isotope analysis by gas chromatography/isotope ratio mass spectrometry (GC/IRMS).<br>The procedure examined is as follows: molecular sieve (type 5A, 200 mg) in 1 ml of isooctane solvent are mixed with a saturated hydrocarbon fraction extracted from an appropriate amount (approx. 20 mg) of crude oil and stayed at room temperatures for more than 3 hours. Long-chain n-alkanes are isolated by extraction with n-hexane after dissolution of the resulting molecular sieve with 47% hydrofluoric acid solution. The recoveries were 90±6% for C₁₅~C₃₄ n-alkanes when their total amounts applied do not exceed 1.4 mg. No effect of the isolation procedure on carbon isotope ratios of n-alkanes was observed.