Studies On Carbon Isotopic Composition And Structural Identification Of Geoporphyrin

With the improvement of gas chromatography-isotope ratio monitoring massspectrometry, its application into petroleum geoscience fOr determining carbonisotopic composition of biomarkers has been one of the most popular researches.Geoporphyrin compounds, owing to their low volatility, can not readily amenable toGC-IRMS analysis. The researches of porphyrin carbon isotope are limited becausethe conventional method is time consuming and needs several mg of individualporphyrin.In this paper, synthesizing bis-(tert-butyldimethylsilony) silicon (IV) porphyrinby derivative reagent, makes porphyrin readily amendable to GC-MS,GC-IRMSananlysis. The synthetic condition which can affects the reaction yield in each step isdiscussed in detail. The last synthetic condition that is used has better repeatable andhigher yield. The analysis of carbon isotopic composition of etio I as the form offree base, nickel, demetallation derivative, silicon(IV) and [(TBDMSO)2Si(IV)] haveshown that etio I porphyrin has no obvious isotope fractionation in the wholesynthesis of [(TBDMSO)2Si(IV)] porphyrin procedure. The carbon isotope study onthe porphyrin mixtures of etio I and OEP indicate that isotope exchange betweenporphyirns during the synthesis of [(TBDMSO)2Si(IV)] porphyrin is absent. Thismethod can be employed for the determination of porphyrin carbon isotopecompositions. It has not found in formal report up to date.This method is applied to the δ13C determination of geoporphyrins fromMaoming and Jianghan oil shales. The δ13C values of C31 DPEP1,C31 DPEP2 and C32DPEP porphyrins in the Jianghan oil shale are -23.5‰, -23.1‰, and -22.1‰,respectively, it seems to be derived from chlorophyll; and C31 DPEP, C32 DPEP andC32 etio porphyrins in the Maoming oil shale give the δ13C values of -26.7‰, -23. 1‰and -26.9‰ respectively. It is proposed C32DPEP come from chlorophyll, andC32etio and C31DPEP geoporphyrin have other origins. The combinative study ofporphyrin and other biomarkers is an effective tool for the carbon isotopic analysis.Earlier studies stated that geoporphyrins are complex mixtures. The structuralidentification of geoporphyrin is a fundamental research.In this paPer the individual geoporphyrin of the Jianghan oil sarnple is separatedand prepared by normal-phase high performance liquid chromatography (HPLC ).The purity of compound is higher than 95%, can suitable for structural identificationby NMR. The combinative study of iH NMR and two-dimensiotial COSY. NOSEY'H N'MR is a precise and reliable tool for the structural identification of individualporphyrin. In china, it has few studies in the structural identification of individualbiomarkers. This research can enhance the level in the study of' molecular organicgeochemistry...