Application of Oxyreactive Thermal Analysis to the examination of organic matter associated with rocks

Organic matter associated with rocks was examined by means of thermal analysis using a new methodology in oxidising conditions. This procedure has been named “Oxyreactive Thermal Analysis” (OTA). The OTA results presented in this study characterise samples from sedimentary rock complexes in terms of their age, and of variations in the associated organic matter arising from different precursors and degree of severity of subsequent transformation processes to which it has been subjected. The results of the OTA method make it possible to estimate the temperature of maturation, to describe the process of evolution of the organic matter, and to distinguish genetic features of its carbonised and metamorphosed products.     

Analysis of organic matter from witwatersrand basin (South Africa) by OTA and Py-GC-MSPreliminary results

Oxyreactive Thermal Analysis (OTA) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) have been performed on highly matured, uraniferous samples. Organic matter investigated by OTA gives two exothermic peaks on DTA curves. The dominant peak appearing at temperature higher than 500°C, confirm the high maturity of the organic matter. Results of analysis by Py-GC-MS complement the OTA results. The organic matter in all of the samples shows the same general pyrolysis characteristics. The pyrograms are dominated by low molecular mass aromatic hydrocarbons. The samples differ in relative abundances of the compounds. The changes in temperature and intensity of the lower-temperature peak in OTA method and differences in relative abundances of aromatic hydrocarbons were used to investigate differences in thermal maturity of the organic matter. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal and spectral properties of halogenosalicylato-Cu(II) complexes

The paper presents the applicability of oxyreactive thermal analysis (OTA) for the investigation of different kinds of resins both natural (recent and fossil) and synthetic. For comparative reasons and a more precise interpretation, along with OTA infrared spectroscopy was used as a method commonly applied for the investigation of fossil resins. The results obtained prove that the OTA method may be very useful for diversification of different kinds of resins. The parameter most valuable for the preliminary characteristics of resins and the evaluation of their transformation was found to be the mass loss recorded on TG curves in three definite temperature ranges. This revised version was published online in July 2006 with corrections to the Cover Date.     

沉积有机质的加氢热解及其地球化学信息研究

用加氢热解(hydropyrolysis)释放高演化源岩干酪根和沥青分子网络中共价键结合的生物标志物,在恢复原始有机地球化学信息方面具有重要的意义,可应用于源岩有机质生源确定、成熟度确定、古沉积环境判识以及油/源对比等.实验表明,样品沥青“A“与加氢热解产物中生物标志物的组成存在一定的差异,加氢热解产物中含有丰富的地球化学信息.加氢热解具有产物收率高、结构重排少、生物特征保持完整等特点,能够合理地释放出沉积有机质分子骨架中具有原生性的组分,保持完整的原始生物标志物结构和立体化学特征.加氢热解技术为油气地球化学研究开辟了新途径.     

Schistes bitumineux de Timahdit (Maroc) : composition et propriétés physicochimiques

The oil shales of Timahdit (Morocco) constitute an important resource in energy. Indeed, the total organic matter is mainly constituted by kerogen. The elementary analysis gives atomic ratios H/C and O/C that are characteristic of a type II kerogen, poorly evolved, constituent of a good mother-rock. The different constituents separated from extractible organic matter by column or thin layer chromatography have been characterized. The analysis of saturated and aromatic hydrocarbons by gas chromatography has proved that the organic matter of the shales of Timahdit is immature, resulting essentially from a phytoplanctonic biomass (marine origin) with a small continental influence. These results have been confirmed by the spectroscopic study of vanadyl and nickel petroporphyrins (DPEP and Etio) isolated from the organic matter of the Timahdit shales.     

Kerogen as a geochemical marker of the thermal history of rocks

The study presents examples of the application of oxyreactive thermal analysis to the geological prospecting of bitumen deposits. Thermal analysis performed under properly chosen analytical conditions allows determination of characteristic features of organic matter and, at the same time, estimation of the thermal history of rocks. Thermal oxyreactivity curves document whether rocks were heated before or not. The results of the oxyreactive thermal analysis correlate well with the results of routine chemical analyses of organic matter (e.g. the composition of kerogen and bituminous fraction, Rock-Eval analysis and others). Our study clearly demonstrates that the composition of organic matter in facially, lithostratigraphically, and biogenetically identical rocks depends on their thermal history.     

Application of different thermal analysis techniques for the evaluation of petroleum source rocks

In the paper, various laboratory pyrolytic methods were used to evaluate selected petroleum source rocks. The methods used are: Rock–Eval pyrolysis, Py–GC pyrolytic technique and TG/DTG/DSC. The experiments of the last method were performed according to three different procedures. Each of them provided different, specific data. The selected rock sample material was diversified in terms of stratigraphical position, structural unit and place of collection (outcrop or borehole). Based on the Rock–Eval analysis results, kerogen in samples can be classified as type II. Additional information on the quality of pyrolysis products was obtained from the Py–GC analysis. Thanks to the combination of the all three implemented pyrolytic techniques, the quality of the generation potential of the source rocks can be evaluated in details. In some samples, the oxidation and pyrolysis of organic matter occur in two stages, what is the evidence of the complex nature of the organic substance. The maximum of pyrolysis reaction is detected by TG/DTG measurement in the range of temperature from 450 to 580 °C, depending on the maturity of organic matter. The maturity level increases with the rock stratigraphic position. The proportions of loss in mass observed in respective stages of pyrolysis in course of TG/DTG experiment are in correspondence with the observations of the released fractions in the Py–GC analysis. The Carpathian Menilite shales could be classified as source rocks with high oil generation potential. Also, the Lower Silurian and Ordovician shales are characterized by high oil-producing potential with a lower content of mineral matter. Cambrian rocks show a different character and gas-prone generation potential.

     

Thermal Analysis of Hydrocarbons in Paleozoic Black Shales

Paleozoic black shales of the Saxothuringikum (Germany) with an average C_org. -content of 0.01 to 20 mass% were investigated with regard to the nature of organic matter. A special pyrolysis technique (DEGAS) was used for a temperature resolved analysis of different hydrocarbons (HC) and the simultaneous detection of inorganic volatiles during heating under vacuum up to 1450°C. The presented data indicate three different forms of organic matter occurring in the investigated black shales (bitumen, kerogen and pyrobitumen). Finally the influence of an igneous dyke intrusion on the alteration of the organic matter was examined. This revised version was published online in July 2006 with corrections to the Cover Date.     

Kinetic Aspect of Thermal Decomposition of Natural Phosphate and its Kerogen. Influence of heating rate and mineral matter

The natural phosphate and its demineralization products from Moroccan deposit were pyrolysed in a thermogravimetric analyser (TG) to examine the influence of the heating rate and mineral matter on their thermal decomposition. The heating rates investigated in the TG were 5–100°C min⁻¹ to final temperature of 1200°C. The integral method was used in the analysis of the TG to determine the kinetic parameters. It has been found that for the natural phosphate and corresponding kerogen analysed in the TG, the increase of the heating rate shifts the maximum rate loss to higher temperature. A first order reaction was found to be adequate for pyrolysis in the range 150–600°C which was attributed to kerogen decomposition. In addition, the results indicate that the removal of mineral matter affected the kinetic parameters found for kerogen in the natural phosphate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Some Applications of Computerized GC-MS to the Determination of Biogenic and Anthropogenic Organic Matter in the Environmentt

Abstract

This is an overview of the application of organic mass spectrometry and ancillary techniques to the analysis of organic matter in environmental research. Such organic matter is usually analyzed in terms of gas, bitumen (lipids), and “kerogen”, with asphaltenes and humic substances for some samples. This approach is illustrated with some examples and the origin, the environmental history and the nature of secondary products of this organic matter can be evaluated by using the data derived from both specific molecular and bulk chemical (also physical) analyses. Evaluations of production and fluxes and cross-correlations can thus be made by the application of the same separation and analytical procedures to samples from different environmental compartments (eg., biota, atmosphere, hydrosphere, lithosphere, etc.).     

Determination of zearalenone and ochratoxin A in soil

Mycotoxins are secondary metabolites, formed by the action of fungi on agricultural crops in the field or during storage. These metabolites are highly toxic to animals and humans and high levels have been measured in agricultural crops. In order to evaluate human risks due to ingestion of mycotoxin-contaminated food different methods have been developed for analysis of mycotoxins in cereals and maize. In this project the focus was on mycotoxins in agricultural soil and the fate of these toxins in the soil-water-plant system. Two different mycotoxins were selected in the study: zearalenone (ZON) produced by species of Fusariumor Aspergillusand ochratoxin A (OTA) produced by species of Penicillium. We developed a method for analysis of these toxins in soil. Soil samples were extracted with methanol-water (9:1) and purified by solid-phase extraction (SPE, C8-columns). The final extract was analysed using high-pressure liquid chromatography (HPLC) with fluorescence detection. A Phenyl Hexyl column was used to separate the toxins. The detection limits obtained were 0.1 and 1.0 microg kg(-1) dry weight (dw) for OTA and ZON, respectively. The developed method has been used for analysis of different soils in connection with growth chamber experiments. The soil types used in the growth chamber experiments were a sandy soil, a sandy clay soil, and a soil with high content of organic matter. The recovery was determined as 85.8 and 93.4% and the repeatability to 5.1 and 12.8% for OTA and ZON, respectively. The reproducibility obtained was 8.5 and 15.0% for soil samples, representing concentration levels from 0.2-30 microg kg(-1) dw (OTA) and from 1.0-100 microg kg(-1) dw (ZON).     

Effects of acid treatments on Moroccan Tarfaya oil shale and pyrolysis of oil shale and their kerogen

In this study, the kerogen of oil shale from Moroccan Tarfaya deposits was isolated and the changes in the initial organic matter during the removal of the mineral matrix were examined. Chloroform extraction of the oil shale increases the intensity of the peaks in the X-ray diffractograms. Infrared spectra and X-ray diffractograms reveal the presence of mineral, calcite, quartz, kaolinite, and pyrite in the mineral matrix of the oil shale. Hydrochloric and hydrofluoric acids dissolution do not alter the organic matter. The nonisothermal weight loss measurements indicate that thermal decomposition of the isolated kerogen can be described by firstorder reaction. A single kinetic expression is valid over the temperature range of kerogen pyrolysis between 433K and 873K. Furthermore, the results indicate that the removal of mineral matter causes a decrease in the activation energies of the pyrolysis reactions of oil shale.     

Subcritical water extraction of organic matter from sedimentary rocks

Subcritical water extraction of organic matter containing sedimentary rocks at 300 °C and 1500 psi produces extracts comparable to conventional solvent extraction. Subcritical water extraction of previously solvent extracted samples confirms that high molecular weight organic matter (kerogen) degradation is not occurring and that only low molecular weight organic matter (free compounds) are being accessed in analogy to solvent extraction procedures. The sedimentary rocks chosen for extraction span the classic geochemical organic matter types. A type I organic matter-containing sedimentary rock produces n-alkanes and isoprenoidal hydrocarbons at 300 °C and 1500 psi that indicate an algal source for the organic matter. Extraction of a rock containing type II organic matter at the same temperature and pressure produces aliphatic hydrocarbons but also aromatic compounds reflecting the increased contributions from terrestrial organic matter in this sample. A type III organic matter-containing sample produces a range of non-polar and polar compounds including polycyclic aromatic hydrocarbons and oxygenated aromatic compounds at 300 °C and 1500 psi reflecting a dominantly terrestrial origin for the organic materials. Although extraction at 300 °C and 1500 psi produces extracts that are comparable to solvent extraction, lower temperature steps display differences related to organic solubility. The type I organic matter produces no products below 300 °C and 1500 psi, reflecting its dominantly aliphatic character, while type II and type III organic matter contribute some polar components to the lower temperature steps, reflecting the chemical heterogeneity of their organic inventory. The separation of polar and non-polar organic compounds by using different temperatures provides the potential for selective extraction that may obviate the need for subsequent preparative chromatography steps. Our results indicate that subcritical water extraction can act as a suitable replacement for conventional solvent extraction of sedimentary rocks, but can also be used for any organic matter containing mineral matrix, including soils and recent sediments, and has the added benefit of tailored extraction for analytes of specific polarities.     

催化加氢热解/气相色谱-质谱研究沉积物中生物标志物

针对地质体中高演化沉积有机质,应用催化加氢热解/气相色谱-质谱方法测定了干酪根中以共价键结合的生物标志物。结果表明,实验样品的催化加氢热解产物收率明显高于二氯甲烷（DCM）索氏抽提,产物色谱图中饱和烃的峰形、保留时间和质谱特征与索氏抽提峰形基本一致;对比两种方法产物中饱和烃主要指标甾烷m/z 217和藿烷m/z 191表明,经过加氢还原,干酪根分子网络中共价键结合着两种生物标志物分子骨架得到印证,为催化加氢热解提取沉积物中生物标志物的方法可靠性提供了依据。催化加氢热解/气相色谱-质谱技术是一种对研究高演化沉积有机质中生物标志化合物有独特作用的有效分析手段。     

Spectrofluorimetric Determination of Ochratoxin a in Wheat and Rice Products Using an Artificial Neural Network

In order to determine Ochratoxin A (OTA) levels in wheat and rice products, an analytical study based on extraction with acetonitrile–water, immunoaffinity column cleanup, and spectrofluorimetric detection for separation and identification of OTA was carried out. The performance of artificial neural networks for modeling the OTA system in spectrofluorimetry was compared with HPLC. Obtained results using these two methods did not show significant differences. Proposed method may be a good alternative to the traditional methods of OTA analysis.     

A modified HPLC method for the determination of ochratoxin A by fluorescence detection

A high-performance liquid chromatographic method (HPLC) with fluorescent detector is described for the determination of ochratoxin A (OTA). A mobile phase consisting of acetonitrile:water:acetic acid (99:99:2, v/v/v) was used for the resolution of the compound on a C(18) Hypersil column. The retention time for OTA and diflunisal which was used as an internal standard (IS) were 11.7 and 12.8 min, respectively. The method is selective, reliable, reproducable with relative standard deviation (RSD) of 1.70 and linear in the range of 2.5 x 10(-9)-1.5 x 10(-8) M OTA. The limit of detection (LOD) and limit of quantification (LOQ) were 2.5 x 10(-10) M corresponding to 0.1 ng mL(-1) and 8.2 x 10(-10) corresponding to 3.3 ng mL(-1), respectively. Recovery studies were 81.2 +/- 1.9 (SD). The method was applied for analysis of OTA in wheat, corn, red pepper, cheese and wine. The proposed method can be used for the routine analysis of OTA in food and animal feed.     

Determination of ochratoxin A at parts-per-trillion levels in cereal products by immunoaffinity column cleanup and high-performance liquid chromatography/mass spectrometry

Ochratoxin A (OTA) is a toxic and potentially carcinogenic fungal toxin found in a variety of food commodities. A new sensitive method has been developed to quantify OTA in cereal products by reversed-phase liquid chromatography (LC) with mass spectrometric (MS) detection. Ochratoxin B was used as the internal standard. OTA was extracted from cereal products with acetonitrile-water, and the extract was diluted with a buffer; the diluted extract was cleaned up on an immunoaffinity column before LC/MS analysis. Two multiple-reaction monitoring transitions were used, one for quantification of OTA and one for confirmation of identity. The method was shown to be highly sensitive, with a low decision limit (CCalpha) of 0.012 microg/kg and a detection capability (CCbeta) of 0.021 microg/kg. Within-laboratory repeatability coefficient of variation values were 7.1, 3.7, and 3.1%, and the corresponding recoveries were 104, 106, and 103% for rice samples fortified with OTA at 0.05, 0.10, and 0.15 microg/kg, respectively. Method validation was performed according to the criteria of European Commission Decision 2002/657/EC. All criteria as presented in the Commission Decision were fulfilled. This method is the first fully validated method using immunoaffinity chromatography for cleanup and MS for detection in the analysis of cereals for OTA. The method was also successfully applied to cereal-derived products. The analytical results for determination of the OTA content of cereal products commercially available in Hong Kong are also reported.     

Liquid chromatographic methods for biotransformation studies of ochratoxin A

Liquid chromatographic methods were used for the detection of ochratoxin A (OTA) and its metabolites ochratoxin alpha (OTalpha), 10-hydroxy OTA (10-OHOTA), 4R-hydroxy OTA (4R-OHOTA) and the ethyl ester of OTA (OTC) in in vitro samples, obtained with Caco-2 cell culture experiments and in in vivo urine samples from sheep. A high-performance liquid chromatography method with fluorescence detection (HPLC-FLD) and a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method were developed and validated for the detection of OTA and its metabolites OTalpha, 10-OHOTA, 4R-OHOTA and OTC, which was used as internal standard. The LOD/LOQ values for OTalpha, 4R-OHOTA and OTA were 0.63/2.11, 0.99/3.31 and 0.84/2.81 microg/L, respectively, for the HPLC-FLD method and 0.98/3.28, 1.11/3.72 and 0.88/2.96 microg/L, respectively for the LC-MS/MS method. Within-day and between-day precision were both <12% for the HPLC-FLD method, and <10% for the LC-MS/MS method. The recovery of OTA and its metabolites ranged between 71 and 111% for the HPLC-FLD method and between 79 and 110 % for the LC-MS/MS method. In the first experiment only OTA was added to the Caco-2 cells while in the second experiment 3-methylcholanthrene (3MC) was also present in the cell culture systems. Besides OTA, which was recovered in all the samples, an unknown compound was also observed in the second experiment. When 3MC was added, the results showed that the OTA concentration in the basolateral samples was decreased by 50%. The methods were also implemented for the analysis of urine samples of sheep, fed increasing amounts of OTA. With the HPLC-FLD method it could be concluded that the concentration of OTA and OTalpha increased according to ingested amounts of OTA, with OTalpha being the most abundant compound. The results obtained with the LC-MS/MS method confirmed these results. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Thermal decomposition of kerogens: Mechanism and analytical application

Specific features of the chemical structures of organic matter (Lerogen) in oil shales caused by the nature of the starting materials for the formation of shales and the routes of their subsequent alteration are reflected in the composition of shale semicoking (retorting) oil. In order to establish the analytical possibilities of the thermal decomposition method in elucidating the kerogen structure and to obtain more data on the mechanism of the pyrolysis of kerogens, the effect of a series of factors (rate of heating, pressure, presence of carrier gases, water and mineral matter of shale, treatment with reagents) on the yield and composition of the pyrolysis products of oil shales was investigated.The yield of shale oil and the phenol content in the latter increase when semicoking is performed in a stream of hydrogen at atmospheric pressure. In shale pyrolysis in the presence of water under pressure, the yield of oil and, in particular, water-soluble organic compounds also increase, as well as the content of neutral heteroatomic compounds in oil. With increasing content of mineral substances in shale, the yield of the semicoking oil (kerogen basis) and the content of polar compounds in it diminish owing to an increasing influence of oil adsorption on the mineral matter and its additional decomposition as a result.In the initial stage of thermal decomposition, both longer aliphatic substituents and side-chains of iso-structures split off and alkenes with a double bond in the middle of the chain (probably the products of elimination and dehydration of the aliphatic substituents with a hydroxyl group) are formed. The formation of n-1-alkenes, particularly those of even carbon number, which originate from the side-chains of odd carbon number by the cleavage of carbon–carbon bonds in the β-position to the cyclic nucleus of kerogen, becomes more pronounced in the final stage of pyrolysis when, owing to significant aromatization of the cyclic part of kerogen, the selectivity of the β-cleavage increases.     

Biogeological Raman spectroscopic studies of Antarctic lacustrine sediments

Analysis of lacustrine sediments is an accepted method for deciphering the palaeoenvironment of a lake's catchment area, as each strata of the sediment gives information about the rock type it was eroded from and also the state of the lake, i.e. oxic or anoxic. Antarctica has long been accepted as a putative analogue for Mars, so the analysis of Antarctic material may give results that can be compared to sediments on Mars. Raman spectroscopy has been selected as the method of analysis as it does not destroy the sample, can be used in situ and requires very little sample preparation. It is a suitable method for analysing both inorganic and organic matter and a miniature spectrometer is currently being developed for use in the field. The results from the spectrometers can serve as a guide for analysing sediments on Mars. It has been shown that Raman spectroscopy can detect and differentiate between oxic and anoxic sediments. Both 1064 and 785 nm wavelengths are suitable for laser excitation of organic and inorganic matter.