Search or filter publications

Filter by type:

Filter by publication type

Filter by year:



  • Showing results for:
  • Reset all filters

Search results

  • Journal article
    Watson JS, Sephton MA, Gilmour I, 2010,

    Thermochemolysis of the Murchison meteorite: identification of oxygen bound and occluded units in the organic macromolecule

    , INT J ASTROBIOL, Vol: 9, Pages: 201-208, ISSN: 1473-5504

    An organic macromolecular residue, prepared from the Murchison meteorite by treatment with hydrofluoric and hydrochloric acids, was subjected to online thermochemolysis with tetramethylammonium hydroxide (TMAH). The most abundant compound released by thermochemolysis was benzoic acid. Other abundant compounds include methyl and dimethyl benzoic acids as well as methoxy benzoic acids. Short chain dicarboxylic acids (C4–8) were also released from the organic macromolecule. Within the C1 and C2 benzoic acids all possible structural isomers are present reflecting the abiotic origin of these units. The most abundant isomers include 3,4-dimethylbenzoic acid (DMBA), 3,5-DMBA, 2,6-DMBA and phenylacetic acid. Thermochemolysis also liberates hydrocarbons that are not observed during thermal desorption; these compounds include naphthalene, methylnaphthalenes, biphenyl, methylbiphenyls, acenaphthylene, acenaphthene, phenanthrene, anthracene, fluoranthene and pyrene. The lack of oxygen containing functional groups in these hydrocarbons indicates that they represent non-covalently bound, occluded molecules within the organic framework. This data provides a valuable insight into oxygen bound and physically occluded moieties in the Murchison organic macromolecule and implies a relative order of synthesis or agglomeration for the detected organic constituents.

  • Journal article
    Court RW, Baki AO, Sims MA, Cullen D, Sephton MAet al., 2010,

    Novel solvent systems for in situ extraterrestrial sample analysis

    , PLANET SPACE SCI, Vol: 58, Pages: 1470-1474, ISSN: 0032-0633

    The life marker chip (LMC) is being designed to test for the chemical signature of life in the soil and rocks of Mars. It will use an antibody array as part of its detection and characterisation system and aims to detect both polar and non-polar molecules at the sub-ppm to tens of ppb level. It is necessary to use a solvent to transfer organic compounds from the Martian samples to the LMC itself, but organic solvents such as dichloromethane or hexane, commonly used to dissolve non-polar molecules, are incompatible with the LMC antibodies. Hence, an aqueous-based solvent capable of dissolving the biomarkers that might exist in the soil or rocks of Mars is required. Solvent extractions of a Martian soil analogue, JSC Mars-1, spiked with a range of standards show that a 20:80 (vol:vol) mixture of methanol and water is incapable of extracting compounds insoluble in water. However, addition of 1.5 mg ml−1 of the surfactant polysorbate 80 produces extraction efficiencies of the aliphatic standards, hexadecane and phytane, equal to 25–30% of those produced by the common organic solvent mixture 93:7 (vol:vol) dichloromethane:methanol. Extraction of squalene and stigmasterol using the polysorbate solution is less efficient but still successful, at 5–10% of the efficiency of 93:7 dichloromethane:methanol. Such aliphatic compounds with occasional functional groups represent the compound classes to which most fossil organic biomarkers belong. The polysorbate solution did not extract the aromatic compounds pyrene and anthracene with great efficiency. A solvent of 20:80 methanol:water with 1.5 mg ml−1 polysorbate 80 is therefore capable of selectively extracting aliphatic biomarkers from Martian samples and transferring them to the antibody sites on the life marker chip.

  • Journal article
    Sephton MA, 2010,

    Organic Geochemistry and the Exploration of Mars

    , J COSMOLOGY, Vol: 5, Pages: 1141-1149

    The Red Planet provides a relatively accessible world on which theories of life’s diversity and origin can be tested. Such examinations are imminent with a number of missions to Mars forthcoming. These missions contain several life detection instruments that will sample the surface and subsurface. Organic geochemical knowledge from terrestrial studies can inform our search for organic matter in Mars rocks. Recent data on Mars minerals and atmospheric gases suggest which methods may be most useful to access any organic records present. A mineralogically-diverse Mars provides varying opportunities for the preservation of past and present life. Extinct or extant life will occupy specific size fractions that must be targeted. Studies suggest that methane is most likely derived from the subsurface. Even if abiotic in origin, the combination of reduced gases and oxidised minerals provides opportunities for life. In the near subsurface methane may be polymerised by cosmic radiation to form abiotic organic matter. This paper considers terrestrial approaches that may be useful in a Martian context.

  • Journal article
    Meredith W, Gomes RL, Cooper M, Snape CE, Sephton MAet al., 2010,

    Hydropyrolysis over a platinum catalyst as a preparative technique for the compound-specific carbon isotope ratio measurement of C27 steroids

    , RAPID COMMUN MASS SP, Vol: 24, Pages: 501-505, ISSN: 1097-0231

    Compound-specific stable carbon isotope analysis by gas chromatography/combustion/isotope ratio mass spectrometry (GC/C/IRMS) is an important method for the determination of the 13C/12C ratios of biomolecules such as steroids, for a wide range of applications. However, steroids in their natural form exhibit poor chromatographic resolution, while derivatisation adds carbon thereby corrupting the stable isotopic composition. Hydropyrolysis with a sulphided molybdenum catalyst has been shown to defunctionalise the steroids, while leaving their carbon skeleton intact, allowing for the accurate measurement of carbon isotope ratios. The presence of double bonds in unsaturated steroids such as cholesterol resulted in significant rearrangement of the products, but replacing the original catalyst system with one of platinum results in higher conversions and far greater selectivity. The improved chromatographic performance of the products should allow GC/C/IRMS to be applied to more structurally complex steroid hormones and their metabolites.

  • Book chapter
    Verchovsky AB, Sephton MA, 2010,

    Noble Gases - Space

    , The Encyclopedia of Mass Spectrometry, Editors: Gross, Houk, Publisher: Elsevier Science Ltd, ISBN: 9780080438047

    In addition to accelerator mass spectrometry and isotope ratio mass spectrometry (formeasurement of isotope abundances in nature), the work reviews ionization ...

  • Journal article
    Court RW, Sephton MA, 2009,

    Meteorite ablation products and their contribution to the atmospheres of terrestrial planets: An experimental study using pyrolysis-FTIR

    , GEOCHIM COSMOCHIM AC, Vol: 73, Pages: 3512-3521, ISSN: 0016-7037
  • Journal article
    Court RW, Sephton MA, 2009,

    Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars

    , EARTH PLAN SCI LETT, Vol: 288, Pages: 382-385, ISSN: 0012-821X

    The presence of methane in the atmosphere of Mars has been suggested as evidence of life, as methane has a short lifetime in the atmosphere of Mars of just a few hundred years, requiring replacement by mechanisms, continuous or episodic, such as biology, volcanism, serpentinization of ultramafic crust or large cometary or asteroidal impacts. The potential of meteoritic infall to deliver significant quantities of methane is restricted by the low abundance of free methane in carbonaceous meteorites. However, the delivery of meteoritic material to the surface of a planet is an energetic process, and the ability of carbonaceous meteorites to generate methane upon ablation during atmospheric entry has not been previously considered. Here, we use analytical pyrolysis to simulate the ablation and pyrolysis of carbonaceous micrometeorites upon atmospheric entry, and Fourier-transform infrared spectroscopy to quantify the subsequent yield of methane. We show that ablation produces a yield of methane that is approximately two orders of magnitude greater than the measured free methane present in the CM2 carbonaceous chondrite, Murchison, but that this previously overlooked source of methane can only account for less than 10 kg of methane annually, a mass far below that required to maintain the abundance of methane observed in the atmosphere of Mars. Our data support attempts to search for life and explore subsurface chemical processes on the Red Planet.

  • Journal article
    Peeters Z, Quinn R, Martins Z, Sephton MA, Becker L, van Loosdrecht MCM, Brucato J, Grunthaner F, Ehrenfreund Pet al., 2009,

    Habitability on planetary surfaces: interdisciplinary preparation phase for future Mars missions

    , INT J ASTROBIOL, Vol: 8, Pages: 301-315, ISSN: 1473-5504

    Life on Earth is one of the outcomes of the formation and evolution of our solar system and has adapted to every explored environment on planet Earth. Recent discoveries have shown that life can exist in extreme environments, such as hydrothermal vents, in deserts and in ice lakes in Antarctica. These findings challenge the definition of the ‘planetary habitable zone’. The objective of future international planetary exploration programmes is to implement a long-term plan for the robotic and human exploration of solar system bodies. Mars has been a central object of interest in the context of extraterrestrial life. The search for extinct or extant life on Mars is one of the main goals of space missions to the Red Planet during the next decade. In this paper we describe the investigation of the physical and chemical properties of Mars soil analogues collected in arid deserts. We measure the pH, redox potential and ion concentrations, as well as carbon and amino acid abundances of soils collected from the Atacama desert (Chile and Peru) and the Salten Skov sediment from Denmark. The samples show large differences in their measured properties, even when taken only several meters apart. A desert sample and the Salten Skov sediment were exposed to a simulated Mars environment to test the stability of amino acids in the soils. The presented laboratory and field studies provide limits to exobiological models, evidence on the effects of subsurface mineral matrices, support current and planned space missions and address planetary protection issues.

  • Journal article
    Perry RS, Sephton MA, 2009,

    Reply to comments on defining biominerals and organominerals: Direct and indirect indicators of life [Perry et al., Sedimentary Geology, 201, 157-179]

    , SED GEOL, Vol: 213, Pages: 156-156, ISSN: 0037-0738
  • Book chapter
    Martins Z, Sephton MA, 2009,

    Extraterrestrial amino acids

    , Origins and Synthesis of Amino Acids., Editors: Hughes, Hughes, Weinheim, Publisher: Wiley-VCH, Pages: 3-42, ISBN: 9789783527324
  • Journal article
    Court RW, Sephton MA, 2009,

    Quantitative flash pyrolysis Fourier transform infrared spectroscopy of organic materials

    , Analytica Chimica Acta, Vol: 639, Pages: 62-66, ISSN: 0003-2670

    Thermal degradation is a common technique used to investigate the nature of organic materials. However, existing methods for the Fourier transform infrared (FTIR) identification and quantification of volatile products from the thermal degradation of organic materials are limited to the technique of thermogravimetric analysis (TGA)–FTIR, which utilizes relatively low heating rates. However, the thermal degradation products of organic materials are known to vary depending on the rate of heating, with lower heating rates of biomass associated with increased yields of solid char and decreased yields of volatiles, as well as a greater opportunity for secondary reactions between the residue and the pyrolysis products. Hence, it is difficult to relate the products of organic matter thermally degraded at <100 °C min−1 in TGA to the products of flash pyrolysis at up to 20,000 °C s−1. We have developed and applied a novel methodology for quantitative flash pyrolysis–FTIR analysis of the volatile pyrolysis products of organic-rich materials. Calibration curves of water, carbon dioxide and methane have been constructed and used to determine absolute volatile release from wood (ash, Lat. Fraxinus). This technique is quicker and simpler than comparable pyrolysis–gas chromatography–mass spectrometry techniques, and avoids errors associated with the lower rates of temperature increase associated with techniques such as thermogravimetric analysis.

  • Journal article
    Gomes RL, Meredith W, Snape CE, Sephton MAet al., 2009,

    Conjugated steroids: analytical approaches and applications

    , ANAL BIOANAL CHEM, Vol: 393, Pages: 453-458, ISSN: 1618-2642

    An introduction to conjugated steroids and the justification for their analysis is provided covering both environmental and biological samples. Determining conjugated steroids or indeed any organic chemical which is conjugated upon excretion from the body has relevance in diagnostic monitoring, forensic screening and environmental analysis (from the endocrine disrupter perspective). The various analytical approaches and the accompanying issues are application-dependent. There are numerous options at each stage of analysis, from extraction, hydrolysis, derivatisation, and detection, and advances can be confined to the specific application for which it was developed. Emphasis is placed on the choice of separation and how gas or liquid chromatography necessitates different preparative stages to enable conjugated steroid determination. Possible future directions and research for conjugated steroid analysis are discussed.

  • Journal article
    Sephton MA, Visscher H, Looy CV, Verchovsky AB, Watson JSet al., 2009,

    Chemical constitution of a Permian-Triassic disaster species

    , GEOLOGY, Vol: 37, Pages: 875-878, ISSN: 0091-7613

    One of the most controversial biological proxies of environmental crisis at the close of the Permian is the organic microfossil Reduviasporonites. The proliferation of this disaster species coincides with the mass extinction and numerous geochemical disturbances. Originally Reduviasporonites was assigned to fungi, opportunistically exploiting dying end-Permian forests, but subsequentgeochemical data have been used to suggest an algal origin. We have used high-sensitivity equipment, partly designed to detect interstellar grains in meteorites, to reexamine the geochemical signature of Reduviasporonites. Organic chemistry, carbon and nitrogen isotopes, and carbon/nitrogen ratios are consistent with a fungal origin. The use of this microfossil as a marker of terrestrial ecosystem collapse should not be merely discounted. Unequivocally diagnostic data, however, may have been precluded by post-burial replacement of its organic constituents.

  • Journal article
    Gomes RL, Meredith W, Snape CE, Sephton MAet al., 2009,

    Analysis of conjugated steroid androgens: Deconjugation, derivatisation and associated issues

    , Journal of Pharmaceutical and Biomedical Analysis, Vol: 49, Pages: 1133-1140, ISSN: 0731-7085

    Gas chromatography/mass spectrometry (GC/MS) is the preferred technique for the detection of urinary steroid androgens for drug testing in athletics. Excreted in either the glucuronide or sulfated conjugated form, steroids must first undergo deconjugation followed by derivatisation to render them suitable for GC analysis. Discussed herein are the deconjugation and the derivatisation preparative options. The analytical challenges surrounding these preparatory approaches, in particular the inability to cleave the sulfate moiety have led to a focus on testing protocols that reply on glucuronide conjugates. Other approaches which alleviate the need for deconjugation and derivatisation are also highlighted.

  • Journal article
    Blyth AJ, Watson JS, 2009,

    Thermochemolysis of organic matter preserved in stalagmites: a preliminary study

    , Organic Geochemistry, Vol: 40, Pages: 1029-1031

    The analysis of organic matter (OM) preserved in stalagmites is a growing field, but there have been few studies of biomarker compounds such as lignin phenols that are widely used in other palaeoenvironmental contexts. Here we present a preliminary qualitative study of the OM in six stalagmite samples from contrasting environments, using thermochemolysis in the presence of tetramethylammonium hydroxide (TMAH). The results indicate that a wide variety of products is preserved, including several potential lignin-derived compounds, but also that further research is needed to maximise compound recovery and allow the analysis of dissolved OM preserved in stalagmites to reach its full potential.

  • Journal article
    Nicoara S, Tonidandel L, Traldi P, Watson J, Morgan G, Popa Oet al., 2009,

    Determining the levels of volatile organic pollutants in urban air using a gas chromatography-mass spectrometry method

    , Journal of Environmental and Public Health

    The paper presents the application of a method based on coupled gas chromatography-mass spectrometry, using an isotopically labelled internal standard for the quantitative analysis of benzene (B), toluene (T), ethyl benzene (E), and o-, m-, p-xylenes (X). Their atmospheric concentrations were determined based on short-term sampling, in different sites of Cluj-Napoca, a highly populated urban centre in N-W Romania, with numerous and diversified road vehicles with internal combustion engines. The method is relatively inexpensive and simple and shows good precision and linearity in the ranges of 7–60 μg/m3 (B), 13–90 μg/m3 (T), 7–50 μg/m3 (E), 10–70 μg/m3 (X-m,p), and 20–130 μg/m3 (X-o). The limits of quantitation/detection of the method LOQ/LOD are of 10/5 μg/m3 (Xo), 5/3 μg/m3 (B, E, X-m,p), and of 3/1 μg/m3 (T), respectively.

  • Book chapter
    Bougeard CMM, Janmohamed IHS, Goslan EH, Jefferson B, Watson JS, Morgan GH, Parsons SAet al., 2008,

    Parameters affecting haloacetic acid and trihalomethane concentrations in treated UK drinking waters

    , Occurrence, Formation, Health Effects, and Control of Disinfection By-Products in Drinking Water, Editors: Karanfil, Krasner, Westerhoff, Xie, Publisher: Oxford University Press, USA, Pages: 95-108, ISBN: 9780841269507
  • Journal article
    Montgomery W, Crowhurst JC, Zaug JM, Jeanloz Ret al., 2008,

    The chemistry of cyanuric acid (H(3)C(3)N(3)O(3)) under high pressure and high temperature

    , JOURNAL OF PHYSICAL CHEMISTRY B, Vol: 112, Pages: 2644-2648, ISSN: 1520-6106
  • Journal article
    Lomax BH, Fraser WT, Sephton MA, Callaghan TV, Self S, Harfoot M, Pyle JA, Wellman CH, Beerling DJet al., 2008,

    Plant spore walls as a record of long-term changes in ultraviolet-B radiation

    , Nature Geoscience, Vol: 1, Pages: 592-596, ISSN: 1752-0894

    Stratospheric ozone screens the Earth's surface from harmful ultraviolet-B radiation. Concentrations of stratospheric ozone are governed by a variety of natural and anthropogenic factors, including solar cycles1, volcanic aerosols2, ozone-depleting substances3 and climate change4. However, assessing this variability before instrumental records has proved difficult owing to the lack of a well-constrained proxy5. Here, we use microspectroscopy to analyse the chemical composition of herbarium samples of clubmoss (Lycophyta) spores originating from high- and low-latitude localities, where they were exposed to different ultraviolet-B histories. We show that the concentration of two ultraviolet-B-absorbing compounds in the walls of high-northern- and southern-latitude spores is strongly regulated by historical variations in ultraviolet-B radiation. Conversely, we find little change in the concentration of these compounds in spores originating from tropical Ecuador, where ultraviolet levels have remained relatively stable. Using spores from Greenland, we reconstruct past (1907–1993) changes in ozone concentration and ultraviolet-B flux; we reveal strong similarities between spore-wall reconstructions, and independent instrumental records6 and model results7. Our findings suggest that ultraviolet-B-absorbing compounds in plant spore walls have the potential to act as a proxy for past changes in terrestrial ultraviolet-B radiation and stratospheric ozone. The chemical signature of plant spore walls in herbaria, and possibly also in sedimentary and ice-core archives, may therefore prove valuable for reconstructing past variations in stratospheric ozone and their connections with changes in solar radiation and climate.

  • Journal article
    Marlow JJ, Martins Z, Sephton MA, 2008,

    Mars on Earth: soil analogues for future Mars missions

    , ASTRON GEOPHYS, Vol: 49, Pages: 20-23, ISSN: 1366-8781

    Preparations for missions to Mars are a major concern for scientists. Predicting how equipment and experiments will perform on the planet is difficult because tests are restricted to Earth. Mars soil analogues are being used to solve this problem. These terrestrial materials are chemically and physically similar to martian soils and, because they contain unusual minerals and trace amounts of organic matter, are scientifically interesting in their own right. However,no current analogue is appropriate for all necessary tests. Here we describe Mars soil analogues, identify limitations and suggest the need for new Mars simulants.

This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.

Request URL: Request URI: /respub/WEB-INF/jsp/search-t4-html.jsp Query String: id=419&limit=20&page=7&respub-action=search.html Current Millis: 1669781629849 Current Time: Wed Nov 30 04:13:49 GMT 2022