Reports: DNI252823-DNI2: Nitrogen Isotopes of Porphyrins from Source Rocks
printer friendly(1) Development of rapid, automated methods for nitrogen and carbon isotope analyses of porphryrins.
The experimental methods outlined in my initial proposal were, at the time, the state of the art and excellent for the proposed work. We were capable of producing nitrogen and carbon isotopic data on nanomolar quantities of N2 and CO2 on a wide range of materials including porphyrins. The system, termed the NanoEA, increases the fraction of sample gas that is directed to the stable isotope mass spectrometer allowing for two orders of magnitude less sample for reliable analyses. This is achieved by trapping of the sample gases using liquid nitrogen and releasing it to a capillary gas chromatography system.
However the old system had limitations in that it was not automated, and had some difficulty handling analysis of carbon and nitrogen isotopes at the same time. I have redesigned the system such that it is fully automated and operated through the instrument software. This removes a potential analytical error involved in the analyses allows the system be run by students, including undergraduates.
(2) Experimental determination of fractionation factors: Here we are trying understanding the nitrogen isotope effects during the formation of metalloporphyins and developing methods for the facile separation of these porphryins from complex mixtures. The works centers on the use of a water soluble porphyrin called tetrakis (4-carboxyphenyl) porphyrin (TCPP) to isolate the metal ligand pair in the simplest mixture possible (aqueous solution, metal salt and porphyin). This is a significant advancement compared to my earlier efforts using organic solvents which had poor yields and required heating. Formation of porphyrins using metal salts and TCPP is simple and proceeds quickly at bench top conditions. Initial work has focused on developing liquid chromatography methods for separating the metallo-free base (no metal) pairs. This has yielded rapid, reproducible HPLC methods that are easily isolated for nitrogen isotope analysis. These samples will also be utilized for metal isotope analyses and may provide useful information for understanding the source and fate of metals (V, Fe, Ni and Zn) in source rocks and oils. We anticipate that this work will be completed by the end of the summer and submitted to Organic Geochemistry.
(3) Environmental samples: We have acquired and collected samples from notable black shale localities from the United States and from ocean drilling cores and are working to understand the broad range of variability in the δ15N of porphyrins. We are focusing our efforts on Devonian black shales of the Mid-Continent region, including New York State. Initial efforts from black shales in western New York did not yield porphyrins in extractable quantities. This has led to the development of using total extract δ15N, which may serve as a suitable proxy for paleoenvironmental analyses. Initial results from this work were presented by Benjamin Uveges at the American Geophysical Union Meeting this past fall.
