The Characterisation of Sedimentary Organic Matter in Carbonates with Fourier-Transform Infrared (FTIR) Spectroscopy
The characterisation of the insoluble macromolecular fraction of sedimentary organic matter preserved in carbonate sediments (also known as kerogen; Durand B, Kerogen: Insoluble Organic Matter from Sedimentary Rocks. Editions Technip, Paris, 1980) allowed
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1 Introduction Fourier-transform infrared spectroscopy (FTIR), an analytic technique based on the interaction between infrared electromagnetic radiation and matter, is of great importance in the characterisation of kerogens. The chemical complexity of kerogens derives from the numerous sources of original organic matter (OM), the selective biodegradation or preservation of organic moieties, and physical and chemical processes leading to diagenesis (Lis et al. 2005a). FTIR studies have revealed bands specific to the chemical structures of complex ˇ erny´ 1955), and kerogen molecules (Painter et al. 1981, 1983; Baruah 1986; C proven their diagnostic value for determining the maturity, type, and oil/gas generation potential of kerogens (Ganz and Kalkreuth 1987; Christy et al. 1989; Kister et al. 1990; Lin and Ritz 1993b; Chen et al. 1998). FTIR is utilised for the identification of organic compounds, both in crystalline and amorphous forms, through the measurement of the energy absorbed by the molecules in transition to different vibrational states. Because each functional group tends to adsorb infrared radiation in a specific wavelength range, it is possible to detect and discriminate different chemical compounds. FTIR can be used to identify a broad range of chemical functional groups in a variety of physical states and it is complementary to other methods such as Raman spectroscopy and gas chromatography–mass spectroscopy (GC–MS). FTIR generally furnishes a better sensitivity for minor components than Raman spectroscopy and provides a comparable ability to classify and identify minerals.
A. Mastandrea (*), A. Guido, F. Demasi, S.A. Ruffolo, and F. Russo Dipartimento di Scienze della Terra, Universita` della Calabria, Via P. Bucci Cubo 15b, I-87036 Rende (CS), Italy e-mail: [email protected]
J. Reitner et al., Advances in Stromatolite Geobiology, Lecture Notes in Earth Sciences 131, DOI 10.1007/978-3-642-10415-2_21, # Springer-Verlag Berlin Heidelberg 2011
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Infrared analysis, however, does not target particular molecules but rather detects classes of molecules. Each organic group (i.e., aliphatic C–H bonds) is present in many compounds with a particular wavelength and this provides a high sensitivity for mixtures (Anderson et al. 2005; Borrego et al. 1995). The major classes of biomolecules readily distinguished by FTIR include (a) proteins, peptides and enzymes, (b) lipids and fatty acids, including cell membranes, (c) carbohydrates and sugars, and (d) nucleic acids. These classes of functional groups have distinct infrared absorption-wavelength ranges (Anderson et al. 2005). The sensitivity of IR analysis for organic molecules, however, depends on the mineral phase and the granular state, and it is increased if the organics are extracted or thermally desorbed and concentrated. With extraction, FTIR can detect organic compounds at parts per billion. Organic matter type and abundance can be used as a measure of benthic secondary productivity, terrestrial/aquatic productivity and org
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